diff options
Diffstat (limited to 'drivers/lguest/x86')
| -rw-r--r-- | drivers/lguest/x86/core.c | 724 | ||||
| -rw-r--r-- | drivers/lguest/x86/switcher_32.S | 388 |
2 files changed, 0 insertions, 1112 deletions
diff --git a/drivers/lguest/x86/core.c b/drivers/lguest/x86/core.c deleted file mode 100644 index b4f79b923aea..000000000000 --- a/drivers/lguest/x86/core.c +++ /dev/null @@ -1,724 +0,0 @@ -/* - * Copyright (C) 2006, Rusty Russell <rusty@rustcorp.com.au> IBM Corporation. - * Copyright (C) 2007, Jes Sorensen <jes@sgi.com> SGI. - * - * This program is free software; you can redistribute it and/or modify - * it under the terms of the GNU General Public License as published by - * the Free Software Foundation; either version 2 of the License, or - * (at your option) any later version. - * - * This program is distributed in the hope that it will be useful, but - * WITHOUT ANY WARRANTY; without even the implied warranty of - * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or - * NON INFRINGEMENT. See the GNU General Public License for more - * details. - * - * You should have received a copy of the GNU General Public License - * along with this program; if not, write to the Free Software - * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. - */ -/*P:450 - * This file contains the x86-specific lguest code. It used to be all - * mixed in with drivers/lguest/core.c but several foolhardy code slashers - * wrestled most of the dependencies out to here in preparation for porting - * lguest to other architectures (see what I mean by foolhardy?). - * - * This also contains a couple of non-obvious setup and teardown pieces which - * were implemented after days of debugging pain. -:*/ -#include <linux/kernel.h> -#include <linux/start_kernel.h> -#include <linux/string.h> -#include <linux/console.h> -#include <linux/screen_info.h> -#include <linux/irq.h> -#include <linux/interrupt.h> -#include <linux/clocksource.h> -#include <linux/clockchips.h> -#include <linux/cpu.h> -#include <linux/lguest.h> -#include <linux/lguest_launcher.h> -#include <asm/paravirt.h> -#include <asm/param.h> -#include <asm/page.h> -#include <asm/pgtable.h> -#include <asm/desc.h> -#include <asm/setup.h> -#include <asm/lguest.h> -#include <linux/uaccess.h> -#include <asm/fpu/internal.h> -#include <asm/tlbflush.h> -#include "../lg.h" - -static int cpu_had_pge; - -static struct { - unsigned long offset; - unsigned short segment; -} lguest_entry; - -/* Offset from where switcher.S was compiled to where we've copied it */ -static unsigned long switcher_offset(void) -{ - return switcher_addr - (unsigned long)start_switcher_text; -} - -/* This cpu's struct lguest_pages (after the Switcher text page) */ -static struct lguest_pages *lguest_pages(unsigned int cpu) -{ - return &(((struct lguest_pages *)(switcher_addr + PAGE_SIZE))[cpu]); -} - -static DEFINE_PER_CPU(struct lg_cpu *, lg_last_cpu); - -/*S:010 - * We approach the Switcher. - * - * Remember that each CPU has two pages which are visible to the Guest when it - * runs on that CPU. This has to contain the state for that Guest: we copy the - * state in just before we run the Guest. - * - * Each Guest has "changed" flags which indicate what has changed in the Guest - * since it last ran. We saw this set in interrupts_and_traps.c and - * segments.c. - */ -static void copy_in_guest_info(struct lg_cpu *cpu, struct lguest_pages *pages) -{ - /* - * Copying all this data can be quite expensive. We usually run the - * same Guest we ran last time (and that Guest hasn't run anywhere else - * meanwhile). If that's not the case, we pretend everything in the - * Guest has changed. - */ - if (__this_cpu_read(lg_last_cpu) != cpu || cpu->last_pages != pages) { - __this_cpu_write(lg_last_cpu, cpu); - cpu->last_pages = pages; - cpu->changed = CHANGED_ALL; - } - - /* - * These copies are pretty cheap, so we do them unconditionally: */ - /* Save the current Host top-level page directory. - */ - pages->state.host_cr3 = __pa(current->mm->pgd); - /* - * Set up the Guest's page tables to see this CPU's pages (and no - * other CPU's pages). - */ - map_switcher_in_guest(cpu, pages); - /* - * Set up the two "TSS" members which tell the CPU what stack to use - * for traps which do directly into the Guest (ie. traps at privilege - * level 1). - */ - pages->state.guest_tss.sp1 = cpu->esp1; - pages->state.guest_tss.ss1 = cpu->ss1; - - /* Copy direct-to-Guest trap entries. */ - if (cpu->changed & CHANGED_IDT) - copy_traps(cpu, pages->state.guest_idt, default_idt_entries); - - /* Copy all GDT entries which the Guest can change. */ - if (cpu->changed & CHANGED_GDT) - copy_gdt(cpu, pages->state.guest_gdt); - /* If only the TLS entries have changed, copy them. */ - else if (cpu->changed & CHANGED_GDT_TLS) - copy_gdt_tls(cpu, pages->state.guest_gdt); - - /* Mark the Guest as unchanged for next time. */ - cpu->changed = 0; -} - -/* Finally: the code to actually call into the Switcher to run the Guest. */ -static void run_guest_once(struct lg_cpu *cpu, struct lguest_pages *pages) -{ - /* This is a dummy value we need for GCC's sake. */ - unsigned int clobber; - - /* - * Copy the guest-specific information into this CPU's "struct - * lguest_pages". - */ - copy_in_guest_info(cpu, pages); - - /* - * Set the trap number to 256 (impossible value). If we fault while - * switching to the Guest (bad segment registers or bug), this will - * cause us to abort the Guest. - */ - cpu->regs->trapnum = 256; - - /* - * Now: we push the "eflags" register on the stack, then do an "lcall". - * This is how we change from using the kernel code segment to using - * the dedicated lguest code segment, as well as jumping into the - * Switcher. - * - * The lcall also pushes the old code segment (KERNEL_CS) onto the - * stack, then the address of this call. This stack layout happens to - * exactly match the stack layout created by an interrupt... - */ - asm volatile("pushf; lcall *%4" - /* - * This is how we tell GCC that %eax ("a") and %ebx ("b") - * are changed by this routine. The "=" means output. - */ - : "=a"(clobber), "=b"(clobber) - /* - * %eax contains the pages pointer. ("0" refers to the - * 0-th argument above, ie "a"). %ebx contains the - * physical address of the Guest's top-level page - * directory. - */ - : "0"(pages), - "1"(__pa(cpu->lg->pgdirs[cpu->cpu_pgd].pgdir)), - "m"(lguest_entry) - /* - * We tell gcc that all these registers could change, - * which means we don't have to save and restore them in - * the Switcher. - */ - : "memory", "%edx", "%ecx", "%edi", "%esi"); -} -/*:*/ - -unsigned long *lguest_arch_regptr(struct lg_cpu *cpu, size_t reg_off, bool any) -{ - switch (reg_off) { - case offsetof(struct pt_regs, bx): - return &cpu->regs->ebx; - case offsetof(struct pt_regs, cx): - return &cpu->regs->ecx; - case offsetof(struct pt_regs, dx): - return &cpu->regs->edx; - case offsetof(struct pt_regs, si): - return &cpu->regs->esi; - case offsetof(struct pt_regs, di): - return &cpu->regs->edi; - case offsetof(struct pt_regs, bp): - return &cpu->regs->ebp; - case offsetof(struct pt_regs, ax): - return &cpu->regs->eax; - case offsetof(struct pt_regs, ip): - return &cpu->regs->eip; - case offsetof(struct pt_regs, sp): - return &cpu->regs->esp; - } - - /* Launcher can read these, but we don't allow any setting. */ - if (any) { - switch (reg_off) { - case offsetof(struct pt_regs, ds): - return &cpu->regs->ds; - case offsetof(struct pt_regs, es): - return &cpu->regs->es; - case offsetof(struct pt_regs, fs): - return &cpu->regs->fs; - case offsetof(struct pt_regs, gs): - return &cpu->regs->gs; - case offsetof(struct pt_regs, cs): - return &cpu->regs->cs; - case offsetof(struct pt_regs, flags): - return &cpu->regs->eflags; - case offsetof(struct pt_regs, ss): - return &cpu->regs->ss; - } - } - - return NULL; -} - -/*M:002 - * There are hooks in the scheduler which we can register to tell when we - * get kicked off the CPU (preempt_notifier_register()). This would allow us - * to lazily disable SYSENTER which would regain some performance, and should - * also simplify copy_in_guest_info(). Note that we'd still need to restore - * things when we exit to Launcher userspace, but that's fairly easy. - * - * We could also try using these hooks for PGE, but that might be too expensive. - * - * The hooks were designed for KVM, but we can also put them to good use. -:*/ - -/*H:040 - * This is the i386-specific code to setup and run the Guest. Interrupts - * are disabled: we own the CPU. - */ -void lguest_arch_run_guest(struct lg_cpu *cpu) -{ - /* - * SYSENTER is an optimized way of doing system calls. We can't allow - * it because it always jumps to privilege level 0. A normal Guest - * won't try it because we don't advertise it in CPUID, but a malicious - * Guest (or malicious Guest userspace program) could, so we tell the - * CPU to disable it before running the Guest. - */ - if (boot_cpu_has(X86_FEATURE_SEP)) - wrmsr(MSR_IA32_SYSENTER_CS, 0, 0); - - /* - * Now we actually run the Guest. It will return when something - * interesting happens, and we can examine its registers to see what it - * was doing. - */ - run_guest_once(cpu, lguest_pages(raw_smp_processor_id())); - - /* - * Note that the "regs" structure contains two extra entries which are - * not really registers: a trap number which says what interrupt or - * trap made the switcher code come back, and an error code which some - * traps set. - */ - - /* Restore SYSENTER if it's supposed to be on. */ - if (boot_cpu_has(X86_FEATURE_SEP)) - wrmsr(MSR_IA32_SYSENTER_CS, __KERNEL_CS, 0); - - /* - * If the Guest page faulted, then the cr2 register will tell us the - * bad virtual address. We have to grab this now, because once we - * re-enable interrupts an interrupt could fault and thus overwrite - * cr2, or we could even move off to a different CPU. - */ - if (cpu->regs->trapnum == 14) - cpu->arch.last_pagefault = read_cr2(); - /* - * Similarly, if we took a trap because the Guest used the FPU, - * we have to restore the FPU it expects to see. - * fpu__restore() may sleep and we may even move off to - * a different CPU. So all the critical stuff should be done - * before this. - */ - else if (cpu->regs->trapnum == 7 && !fpregs_active()) - fpu__restore(¤t->thread.fpu); -} - -/*H:130 - * Now we've examined the hypercall code; our Guest can make requests. - * Our Guest is usually so well behaved; it never tries to do things it isn't - * allowed to, and uses hypercalls instead. Unfortunately, Linux's paravirtual - * infrastructure isn't quite complete, because it doesn't contain replacements - * for the Intel I/O instructions. As a result, the Guest sometimes fumbles - * across one during the boot process as it probes for various things which are - * usually attached to a PC. - * - * When the Guest uses one of these instructions, we get a trap (General - * Protection Fault) and come here. We queue this to be sent out to the - * Launcher to handle. - */ - -/* - * The eip contains the *virtual* address of the Guest's instruction: - * we copy the instruction here so the Launcher doesn't have to walk - * the page tables to decode it. We handle the case (eg. in a kernel - * module) where the instruction is over two pages, and the pages are - * virtually but not physically contiguous. - * - * The longest possible x86 instruction is 15 bytes, but we don't handle - * anything that strange. - */ -static void copy_from_guest(struct lg_cpu *cpu, - void *dst, unsigned long vaddr, size_t len) -{ - size_t to_page_end = PAGE_SIZE - (vaddr % PAGE_SIZE); - unsigned long paddr; - - BUG_ON(len > PAGE_SIZE); - - /* If it goes over a page, copy in two parts. */ - if (len > to_page_end) { - /* But make sure the next page is mapped! */ - if (__guest_pa(cpu, vaddr + to_page_end, &paddr)) - copy_from_guest(cpu, dst + to_page_end, - vaddr + to_page_end, - len - to_page_end); - else - /* Otherwise fill with zeroes. */ - memset(dst + to_page_end, 0, len - to_page_end); - len = to_page_end; - } - - /* This will kill the guest if it isn't mapped, but that - * shouldn't happen. */ - __lgread(cpu, dst, guest_pa(cpu, vaddr), len); -} - - -static void setup_emulate_insn(struct lg_cpu *cpu) -{ - cpu->pending.trap = 13; - copy_from_guest(cpu, cpu->pending.insn, cpu->regs->eip, - sizeof(cpu->pending.insn)); -} - -static void setup_iomem_insn(struct lg_cpu *cpu, unsigned long iomem_addr) -{ - cpu->pending.trap = 14; - cpu->pending.addr = iomem_addr; - copy_from_guest(cpu, cpu->pending.insn, cpu->regs->eip, - sizeof(cpu->pending.insn)); -} - -/*H:050 Once we've re-enabled interrupts, we look at why the Guest exited. */ -void lguest_arch_handle_trap(struct lg_cpu *cpu) -{ - unsigned long iomem_addr; - - switch (cpu->regs->trapnum) { - case 13: /* We've intercepted a General Protection Fault. */ - /* Hand to Launcher to emulate those pesky IN and OUT insns */ - if (cpu->regs->errcode == 0) { - setup_emulate_insn(cpu); - return; - } - break; - case 14: /* We've intercepted a Page Fault. */ - /* - * The Guest accessed a virtual address that wasn't mapped. - * This happens a lot: we don't actually set up most of the page - * tables for the Guest at all when we start: as it runs it asks - * for more and more, and we set them up as required. In this - * case, we don't even tell the Guest that the fault happened. - * - * The errcode tells whether this was a read or a write, and - * whether kernel or userspace code. - */ - if (demand_page(cpu, cpu->arch.last_pagefault, - cpu->regs->errcode, &iomem_addr)) - return; - - /* Was this an access to memory mapped IO? */ - if (iomem_addr) { - /* Tell Launcher, let it handle it. */ - setup_iomem_insn(cpu, iomem_addr); - return; - } - - /* - * OK, it's really not there (or not OK): the Guest needs to - * know. We write out the cr2 value so it knows where the - * fault occurred. - * - * Note that if the Guest were really messed up, this could - * happen before it's done the LHCALL_LGUEST_INIT hypercall, so - * lg->lguest_data could be NULL - */ - if (cpu->lg->lguest_data && - put_user(cpu->arch.last_pagefault, - &cpu->lg->lguest_data->cr2)) - kill_guest(cpu, "Writing cr2"); - break; - case 7: /* We've intercepted a Device Not Available fault. */ - /* No special handling is needed here. */ - break; - case 32 ... 255: - /* This might be a syscall. */ - if (could_be_syscall(cpu->regs->trapnum)) - break; - - /* - * Other values mean a real interrupt occurred, in which case - * the Host handler has already been run. We just do a - * friendly check if another process should now be run, then - * return to run the Guest again. - */ - cond_resched(); - return; - case LGUEST_TRAP_ENTRY: - /* - * Our 'struct hcall_args' maps directly over our regs: we set - * up the pointer now to indicate a hypercall is pending. - */ - cpu->hcall = (struct hcall_args *)cpu->regs; - return; - } - - /* We didn't handle the trap, so it needs to go to the Guest. */ - if (!deliver_trap(cpu, cpu->regs->trapnum)) - /* - * If the Guest doesn't have a handler (either it hasn't - * registered any yet, or it's one of the faults we don't let - * it handle), it dies with this cryptic error message. - */ - kill_guest(cpu, "unhandled trap %li at %#lx (%#lx)", - cpu->regs->trapnum, cpu->regs->eip, - cpu->regs->trapnum == 14 ? cpu->arch.last_pagefault - : cpu->regs->errcode); -} - -/* - * Now we can look at each of the routines this calls, in increasing order of - * complexity: do_hypercalls(), emulate_insn(), maybe_do_interrupt(), - * deliver_trap() and demand_page(). After all those, we'll be ready to - * examine the Switcher, and our philosophical understanding of the Host/Guest - * duality will be complete. -:*/ -static void adjust_pge(void *on) -{ - if (on) - cr4_set_bits(X86_CR4_PGE); - else - cr4_clear_bits(X86_CR4_PGE); -} - -/*H:020 - * Now the Switcher is mapped and every thing else is ready, we need to do - * some more i386-specific initialization. - */ -void __init lguest_arch_host_init(void) -{ - int i; - - /* - * Most of the x86/switcher_32.S doesn't care that it's been moved; on - * Intel, jumps are relative, and it doesn't access any references to - * external code or data. - * - * The only exception is the interrupt handlers in switcher.S: their - * addresses are placed in a table (default_idt_entries), so we need to - * update the table with the new addresses. switcher_offset() is a - * convenience function which returns the distance between the - * compiled-in switcher code and the high-mapped copy we just made. - */ - for (i = 0; i < IDT_ENTRIES; i++) - default_idt_entries[i] += switcher_offset(); - - /* - * Set up the Switcher's per-cpu areas. - * - * Each CPU gets two pages of its own within the high-mapped region - * (aka. "struct lguest_pages"). Much of this can be initialized now, - * but some depends on what Guest we are running (which is set up in - * copy_in_guest_info()). - */ - for_each_possible_cpu(i) { - /* lguest_pages() returns this CPU's two pages. */ - struct lguest_pages *pages = lguest_pages(i); - /* This is a convenience pointer to make the code neater. */ - struct lguest_ro_state *state = &pages->state; - - /* - * The Global Descriptor Table: the Host has a different one - * for each CPU. We keep a descriptor for the GDT which says - * where it is and how big it is (the size is actually the last - * byte, not the size, hence the "-1"). - */ - state->host_gdt_desc.size = GDT_SIZE-1; - state->host_gdt_desc.address = (long)get_cpu_gdt_rw(i); - - /* - * All CPUs on the Host use the same Interrupt Descriptor - * Table, so we just use store_idt(), which gets this CPU's IDT - * descriptor. - */ - store_idt(&state->host_idt_desc); - - /* - * The descriptors for the Guest's GDT and IDT can be filled - * out now, too. We copy the GDT & IDT into ->guest_gdt and - * ->guest_idt before actually running the Guest. - */ - state->guest_idt_desc.size = sizeof(state->guest_idt)-1; - state->guest_idt_desc.address = (long)&state->guest_idt; - state->guest_gdt_desc.size = sizeof(state->guest_gdt)-1; - state->guest_gdt_desc.address = (long)&state->guest_gdt; - - /* - * We know where we want the stack to be when the Guest enters - * the Switcher: in pages->regs. The stack grows upwards, so - * we start it at the end of that structure. - */ - state->guest_tss.sp0 = (long)(&pages->regs + 1); - /* - * And this is the GDT entry to use for the stack: we keep a - * couple of special LGUEST entries. - */ - state->guest_tss.ss0 = LGUEST_DS; - - /* - * x86 can have a finegrained bitmap which indicates what I/O - * ports the process can use. We set it to the end of our - * structure, meaning "none". - */ - state->guest_tss.io_bitmap_base = sizeof(state->guest_tss); - - /* - * Some GDT entries are the same across all Guests, so we can - * set them up now. - */ - setup_default_gdt_entries(state); - /* Most IDT entries are the same for all Guests, too.*/ - setup_default_idt_entries(state, default_idt_entries); - - /* - * The Host needs to be able to use the LGUEST segments on this - * CPU, too, so put them in the Host GDT. - */ - get_cpu_gdt_rw(i)[GDT_ENTRY_LGUEST_CS] = FULL_EXEC_SEGMENT; - get_cpu_gdt_rw(i)[GDT_ENTRY_LGUEST_DS] = FULL_SEGMENT; - } - - /* - * In the Switcher, we want the %cs segment register to use the - * LGUEST_CS GDT entry: we've put that in the Host and Guest GDTs, so - * it will be undisturbed when we switch. To change %cs and jump we - * need this structure to feed to Intel's "lcall" instruction. - */ - lguest_entry.offset = (long)switch_to_guest + switcher_offset(); - lguest_entry.segment = LGUEST_CS; - - /* - * Finally, we need to turn off "Page Global Enable". PGE is an - * optimization where page table entries are specially marked to show - * they never change. The Host kernel marks all the kernel pages this - * way because it's always present, even when userspace is running. - * - * Lguest breaks this: unbeknownst to the rest of the Host kernel, we - * switch to the Guest kernel. If you don't disable this on all CPUs, - * you'll get really weird bugs that you'll chase for two days. - * - * I used to turn PGE off every time we switched to the Guest and back - * on when we return, but that slowed the Switcher down noticibly. - */ - - /* - * We don't need the complexity of CPUs coming and going while we're - * doing this. - */ - get_online_cpus(); - if (boot_cpu_has(X86_FEATURE_PGE)) { /* We have a broader idea of "global". */ - /* Remember that this was originally set (for cleanup). */ - cpu_had_pge = 1; - /* - * adjust_pge is a helper function which sets or unsets the PGE - * bit on its CPU, depending on the argument (0 == unset). - */ - on_each_cpu(adjust_pge, (void *)0, 1); - /* Turn off the feature in the global feature set. */ - clear_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE); - } - put_online_cpus(); -} -/*:*/ - -void __exit lguest_arch_host_fini(void) -{ - /* If we had PGE before we started, turn it back on now. */ - get_online_cpus(); - if (cpu_had_pge) { - set_cpu_cap(&boot_cpu_data, X86_FEATURE_PGE); - /* adjust_pge's argument "1" means set PGE. */ - on_each_cpu(adjust_pge, (void *)1, 1); - } - put_online_cpus(); -} - - -/*H:122 The i386-specific hypercalls simply farm out to the right functions. */ -int lguest_arch_do_hcall(struct lg_cpu *cpu, struct hcall_args *args) -{ - switch (args->arg0) { - case LHCALL_LOAD_GDT_ENTRY: - load_guest_gdt_entry(cpu, args->arg1, args->arg2, args->arg3); - break; - case LHCALL_LOAD_IDT_ENTRY: - load_guest_idt_entry(cpu, args->arg1, args->arg2, args->arg3); - break; - case LHCALL_LOAD_TLS: - guest_load_tls(cpu, args->arg1); - break; - default: - /* Bad Guest. Bad! */ - return -EIO; - } - return 0; -} - -/*H:126 i386-specific hypercall initialization: */ -int lguest_arch_init_hypercalls(struct lg_cpu *cpu) -{ - u32 tsc_speed; - - /* - * The pointer to the Guest's "struct lguest_data" is the only argument. - * We check that address now. - */ - if (!lguest_address_ok(cpu->lg, cpu->hcall->arg1, - sizeof(*cpu->lg->lguest_data))) - return -EFAULT; - - /* - * Having checked it, we simply set lg->lguest_data to point straight - * into the Launcher's memory at the right place and then use - * copy_to_user/from_user from now on, instead of lgread/write. I put - * this in to show that I'm not immune to writing stupid - * optimizations. - */ - cpu->lg->lguest_data = cpu->lg->mem_base + cpu->hcall->arg1; - - /* - * We insist that the Time Stamp Counter exist and doesn't change with - * cpu frequency. Some devious chip manufacturers decided that TSC - * changes could be handled in software. I decided that time going - * backwards might be good for benchmarks, but it's bad for users. - * - * We also insist that the TSC be stable: the kernel detects unreliable - * TSCs for its own purposes, and we use that here. - */ - if (boot_cpu_has(X86_FEATURE_CONSTANT_TSC) && !check_tsc_unstable()) - tsc_speed = tsc_khz; - else - tsc_speed = 0; - if (put_user(tsc_speed, &cpu->lg->lguest_data->tsc_khz)) - return -EFAULT; - - /* The interrupt code might not like the system call vector. */ - if (!check_syscall_vector(cpu->lg)) - kill_guest(cpu, "bad syscall vector"); - - return 0; -} -/*:*/ - -/*L:030 - * Most of the Guest's registers are left alone: we used get_zeroed_page() to - * allocate the structure, so they will be 0. - */ -void lguest_arch_setup_regs(struct lg_cpu *cpu, unsigned long start) -{ - struct lguest_regs *regs = cpu->regs; - - /* - * There are four "segment" registers which the Guest needs to boot: - * The "code segment" register (cs) refers to the kernel code segment - * __KERNEL_CS, and the "data", "extra" and "stack" segment registers - * refer to the kernel data segment __KERNEL_DS. - * - * The privilege level is packed into the lower bits. The Guest runs - * at privilege level 1 (GUEST_PL). - */ - regs->ds = regs->es = regs->ss = __KERNEL_DS|GUEST_PL; - regs->cs = __KERNEL_CS|GUEST_PL; - - /* - * The "eflags" register contains miscellaneous flags. Bit 1 (0x002) - * is supposed to always be "1". Bit 9 (0x200) controls whether - * interrupts are enabled. We always leave interrupts enabled while - * running the Guest. - */ - regs->eflags = X86_EFLAGS_IF | X86_EFLAGS_FIXED; - - /* - * The "Extended Instruction Pointer" register says where the Guest is - * running. - */ - regs->eip = start; - - /* - * %esi points to our boot information, at physical address 0, so don't - * touch it. - */ - - /* There are a couple of GDT entries the Guest expects at boot. */ - setup_guest_gdt(cpu); -} diff --git a/drivers/lguest/x86/switcher_32.S b/drivers/lguest/x86/switcher_32.S deleted file mode 100644 index 40634b0db9f7..000000000000 --- a/drivers/lguest/x86/switcher_32.S +++ /dev/null @@ -1,388 +0,0 @@ -/*P:900 - * This is the Switcher: code which sits at 0xFFC00000 (or 0xFFE00000) astride - * both the Host and Guest to do the low-level Guest<->Host switch. It is as - * simple as it can be made, but it's naturally very specific to x86. - * - * You have now completed Preparation. If this has whet your appetite; if you - * are feeling invigorated and refreshed then the next, more challenging stage - * can be found in "make Guest". - :*/ - -/*M:012 - * Lguest is meant to be simple: my rule of thumb is that 1% more LOC must - * gain at least 1% more performance. Since neither LOC nor performance can be - * measured beforehand, it generally means implementing a feature then deciding - * if it's worth it. And once it's implemented, who can say no? - * - * This is why I haven't implemented this idea myself. I want to, but I - * haven't. You could, though. - * - * The main place where lguest performance sucks is Guest page faulting. When - * a Guest userspace process hits an unmapped page we switch back to the Host, - * walk the page tables, find it's not mapped, switch back to the Guest page - * fault handler, which calls a hypercall to set the page table entry, then - * finally returns to userspace. That's two round-trips. - * - * If we had a small walker in the Switcher, we could quickly check the Guest - * page table and if the page isn't mapped, immediately reflect the fault back - * into the Guest. This means the Switcher would have to know the top of the - * Guest page table and the page fault handler address. - * - * For simplicity, the Guest should only handle the case where the privilege - * level of the fault is 3 and probably only not present or write faults. It - * should also detect recursive faults, and hand the original fault to the - * Host (which is actually really easy). - * - * Two questions remain. Would the performance gain outweigh the complexity? - * And who would write the verse documenting it? -:*/ - -/*M:011 - * Lguest64 handles NMI. This gave me NMI envy (until I looked at their - * code). It's worth doing though, since it would let us use oprofile in the - * Host when a Guest is running. -:*/ - -/*S:100 - * Welcome to the Switcher itself! - * - * This file contains the low-level code which changes the CPU to run the Guest - * code, and returns to the Host when something happens. Understand this, and - * you understand the heart of our journey. - * - * Because this is in assembler rather than C, our tale switches from prose to - * verse. First I tried limericks: - * - * There once was an eax reg, - * To which our pointer was fed, - * It needed an add, - * Which asm-offsets.h had - * But this limerick is hurting my head. - * - * Next I tried haikus, but fitting the required reference to the seasons in - * every stanza was quickly becoming tiresome: - * - * The %eax reg - * Holds "struct lguest_pages" now: - * Cherry blossoms fall. - * - * Then I started with Heroic Verse, but the rhyming requirement leeched away - * the content density and led to some uniquely awful oblique rhymes: - * - * These constants are coming from struct offsets - * For use within the asm switcher text. - * - * Finally, I settled for something between heroic hexameter, and normal prose - * with inappropriate linebreaks. Anyway, it aint no Shakespeare. - */ - -// Not all kernel headers work from assembler -// But these ones are needed: the ENTRY() define -// And constants extracted from struct offsets -// To avoid magic numbers and breakage: -// Should they change the compiler can't save us -// Down here in the depths of assembler code. -#include <linux/linkage.h> -#include <asm/asm-offsets.h> -#include <asm/page.h> -#include <asm/segment.h> -#include <asm/lguest.h> - -// We mark the start of the code to copy -// It's placed in .text tho it's never run here -// You'll see the trick macro at the end -// Which interleaves data and text to effect. -.text -ENTRY(start_switcher_text) - -// When we reach switch_to_guest we have just left -// The safe and comforting shores of C code -// %eax has the "struct lguest_pages" to use -// Where we save state and still see it from the Guest -// And %ebx holds the Guest shadow pagetable: -// Once set we have truly left Host behind. -ENTRY(switch_to_guest) - // We told gcc all its regs could fade, - // Clobbered by our journey into the Guest - // We could have saved them, if we tried - // But time is our master and cycles count. - - // Segment registers must be saved for the Host - // We push them on the Host stack for later - pushl %es - pushl %ds - pushl %gs - pushl %fs - // But the compiler is fickle, and heeds - // No warning of %ebp clobbers - // When frame pointers are used. That register - // Must be saved and restored or chaos strikes. - pushl %ebp - // The Host's stack is done, now save it away - // In our "struct lguest_pages" at offset - // Distilled into asm-offsets.h - movl %esp, LGUEST_PAGES_host_sp(%eax) - - // All saved and there's now five steps before us: - // Stack, GDT, IDT, TSS - // Then last of all the page tables are flipped. - - // Yet beware that our stack pointer must be - // Always valid lest an NMI hits - // %edx does the duty here as we juggle - // %eax is lguest_pages: our stack lies within. - movl %eax, %edx - addl $LGUEST_PAGES_regs, %edx - movl %edx, %esp - - // The Guest's GDT we so carefully - // Placed in the "struct lguest_pages" before - lgdt LGUEST_PAGES_guest_gdt_desc(%eax) - - // The Guest's IDT we did partially - // Copy to "struct lguest_pages" as well. - lidt LGUEST_PAGES_guest_idt_desc(%eax) - - // The TSS entry which controls traps - // Must be loaded up with "ltr" now: - // The GDT entry that TSS uses - // Changes type when we load it: damn Intel! - // For after we switch over our page tables - // That entry will be read-only: we'd crash. - movl $(GDT_ENTRY_TSS*8), %edx - ltr %dx - - // Look back now, before we take this last step! - // The Host's TSS entry was also marked used; - // Let's clear it again for our return. - // The GDT descriptor of the Host - // Points to the table after two "size" bytes - movl (LGUEST_PAGES_host_gdt_desc+2)(%eax), %edx - // Clear "used" from type field (byte 5, bit 2) - andb $0xFD, (GDT_ENTRY_TSS*8 + 5)(%edx) - - // Once our page table's switched, the Guest is live! - // The Host fades as we run this final step. - // Our "struct lguest_pages" is now read-only. - movl %ebx, %cr3 - - // The page table change did one tricky thing: - // The Guest's register page has been mapped - // Writable under our %esp (stack) -- - // We can simply pop off all Guest regs. - popl %eax - popl %ebx - popl %ecx - popl %edx - popl %esi - popl %edi - popl %ebp - popl %gs - popl %fs - popl %ds - popl %es - - // Near the base of the stack lurk two strange fields - // Which we fill as we exit the Guest - // These are the trap number and its error - // We can simply step past them on our way. - addl $8, %esp - - // The last five stack slots hold return address - // And everything needed to switch privilege - // From Switcher's level 0 to Guest's 1, - // And the stack where the Guest had last left it. - // Interrupts are turned back on: we are Guest. - iret - -// We tread two paths to switch back to the Host -// Yet both must save Guest state and restore Host -// So we put the routine in a macro. -#define SWITCH_TO_HOST \ - /* We save the Guest state: all registers first \ - * Laid out just as "struct lguest_regs" defines */ \ - pushl %es; \ - pushl %ds; \ - pushl %fs; \ - pushl %gs; \ - pushl %ebp; \ - pushl %edi; \ - pushl %esi; \ - pushl %edx; \ - pushl %ecx; \ - pushl %ebx; \ - pushl %eax; \ - /* Our stack and our code are using segments \ - * Set in the TSS and IDT \ - * Yet if we were to touch data we'd use \ - * Whatever data segment the Guest had. \ - * Load the lguest ds segment for now. */ \ - movl $(LGUEST_DS), %eax; \ - movl %eax, %ds; \ - /* So where are we? Which CPU, which struct? \ - * The stack is our clue: our TSS starts \ - * It at the end of "struct lguest_pages". \ - * Or we may have stumbled while restoring \ - * Our Guest segment regs while in switch_to_guest, \ - * The fault pushed atop that part-unwound stack. \ - * If we round the stack down to the page start \ - * We're at the start of "struct lguest_pages". */ \ - movl %esp, %eax; \ - andl $(~(1 << PAGE_SHIFT - 1)), %eax; \ - /* Save our trap number: the switch will obscure it \ - * (In the Host the Guest regs are not mapped here) \ - * %ebx holds it safe for deliver_to_host */ \ - movl LGUEST_PAGES_regs_trapnum(%eax), %ebx; \ - /* The Host GDT, IDT and stack! \ - * All these lie safely hidden from the Guest: \ - * We must return to the Host page tables \ - * (Hence that was saved in struct lguest_pages) */ \ - movl LGUEST_PAGES_host_cr3(%eax), %edx; \ - movl %edx, %cr3; \ - /* As before, when we looked back at the Host \ - * As we left and marked TSS unused \ - * So must we now for the Guest left behind. */ \ - andb $0xFD, (LGUEST_PAGES_guest_gdt+GDT_ENTRY_TSS*8+5)(%eax); \ - /* Switch to Host's GDT, IDT. */ \ - lgdt LGUEST_PAGES_host_gdt_desc(%eax); \ - lidt LGUEST_PAGES_host_idt_desc(%eax); \ - /* Restore the Host's stack where its saved regs lie */ \ - movl LGUEST_PAGES_host_sp(%eax), %esp; \ - /* Last the TSS: our Host is returned */ \ - movl $(GDT_ENTRY_TSS*8), %edx; \ - ltr %dx; \ - /* Restore now the regs saved right at the first. */ \ - popl %ebp; \ - popl %fs; \ - popl %gs; \ - popl %ds; \ - popl %es - -// The first path is trod when the Guest has trapped: -// (Which trap it was has been pushed on the stack). -// We need only switch back, and the Host will decode -// Why we came home, and what needs to be done. -return_to_host: - SWITCH_TO_HOST - iret - -// We are lead to the second path like so: -// An interrupt, with some cause external -// Has ajerked us rudely from the Guest's code -// Again we must return home to the Host -deliver_to_host: - SWITCH_TO_HOST - // But now we must go home via that place - // Where that interrupt was supposed to go - // Had we not been ensconced, running the Guest. - // Here we see the trickness of run_guest_once(): - // The Host stack is formed like an interrupt - // With EIP, CS and EFLAGS layered. - // Interrupt handlers end with "iret" - // And that will take us home at long long last. - - // But first we must find the handler to call! - // The IDT descriptor for the Host - // Has two bytes for size, and four for address: - // %edx will hold it for us for now. - movl (LGUEST_PAGES_host_idt_desc+2)(%eax), %edx - // We now know the table address we need, - // And saved the trap's number inside %ebx. - // Yet the pointer to the handler is smeared - // Across the bits of the table entry. - // What oracle can tell us how to extract - // From such a convoluted encoding? - // I consulted gcc, and it gave - // These instructions, which I gladly credit: - leal (%edx,%ebx,8), %eax - movzwl (%eax),%edx - movl 4(%eax), %eax - xorw %ax, %ax - orl %eax, %edx - // Now the address of the handler's in %edx - // We call it now: its "iret" drops us home. - jmp *%edx - -// Every interrupt can come to us here -// But we must truly tell each apart. -// They number two hundred and fifty six -// And each must land in a different spot, -// Push its number on stack, and join the stream. - -// And worse, a mere six of the traps stand apart -// And push on their stack an addition: -// An error number, thirty two bits long -// So we punish the other two fifty -// And make them push a zero so they match. - -// Yet two fifty six entries is long -// And all will look most the same as the last -// So we create a macro which can make -// As many entries as we need to fill. - -// Note the change to .data then .text: -// We plant the address of each entry -// Into a (data) table for the Host -// To know where each Guest interrupt should go. -.macro IRQ_STUB N TARGET - .data; .long 1f; .text; 1: - // Trap eight, ten through fourteen and seventeen - // Supply an error number. Else zero. - .if (\N <> 8) && (\N < 10 || \N > 14) && (\N <> 17) - pushl $0 - .endif - pushl $\N - jmp \TARGET - ALIGN -.endm - -// This macro creates numerous entries -// Using GAS macros which out-power C's. -.macro IRQ_STUBS FIRST LAST TARGET - irq=\FIRST - .rept \LAST-\FIRST+1 - IRQ_STUB irq \TARGET - irq=irq+1 - .endr -.endm - -// Here's the marker for our pointer table -// Laid in the data section just before -// Each macro places the address of code -// Forming an array: each one points to text -// Which handles interrupt in its turn. -.data -.global default_idt_entries -default_idt_entries: -.text - // The first two traps go straight back to the Host - IRQ_STUBS 0 1 return_to_host - // We'll say nothing, yet, about NMI - IRQ_STUB 2 handle_nmi - // Other traps also return to the Host - IRQ_STUBS 3 31 return_to_host - // All interrupts go via their handlers - IRQ_STUBS 32 127 deliver_to_host - // 'Cept system calls coming from userspace - // Are to go to the Guest, never the Host. - IRQ_STUB 128 return_to_host - IRQ_STUBS 129 255 deliver_to_host - -// The NMI, what a fabulous beast -// Which swoops in and stops us no matter that -// We're suspended between heaven and hell, -// (Or more likely between the Host and Guest) -// When in it comes! We are dazed and confused -// So we do the simplest thing which one can. -// Though we've pushed the trap number and zero -// We discard them, return, and hope we live. -handle_nmi: - addl $8, %esp - iret - -// We are done; all that's left is Mastery -// And "make Mastery" is a journey long -// Designed to make your fingers itch to code. - -// Here ends the text, the file and poem. -ENTRY(end_switcher_text) |