diff options
Diffstat (limited to 'arch/x86/hyperv/hv_crash.c')
| -rw-r--r-- | arch/x86/hyperv/hv_crash.c | 642 |
1 files changed, 642 insertions, 0 deletions
diff --git a/arch/x86/hyperv/hv_crash.c b/arch/x86/hyperv/hv_crash.c new file mode 100644 index 000000000000..c0e22921ace1 --- /dev/null +++ b/arch/x86/hyperv/hv_crash.c @@ -0,0 +1,642 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * X86 specific Hyper-V root partition kdump/crash support module + * + * Copyright (C) 2025, Microsoft, Inc. + * + * This module implements hypervisor RAM collection into vmcore for both + * cases of the hypervisor crash and Linux root crash. Hyper-V implements + * a disable hypercall with a 32bit protected mode ABI callback. This + * mechanism must be used to unlock hypervisor RAM. Since the hypervisor RAM + * is already mapped in Linux, it is automatically collected into Linux vmcore, + * and can be examined by the crash command (raw RAM dump) or windbg. + * + * At a high level: + * + * Hypervisor Crash: + * Upon crash, hypervisor goes into an emergency minimal dispatch loop, a + * restrictive mode with very limited hypercall and MSR support. Each cpu + * then injects NMIs into root vcpus. A shared page is used to check + * by Linux in the NMI handler if the hypervisor has crashed. This shared + * page is setup in hv_root_crash_init during boot. + * + * Linux Crash: + * In case of Linux crash, the callback hv_crash_stop_other_cpus will send + * NMIs to all cpus, then proceed to the crash_nmi_callback where it waits + * for all cpus to be in NMI. + * + * NMI Handler (upon quorum): + * Eventually, in both cases, all cpus will end up in the NMI handler. + * Hyper-V requires the disable hypervisor must be done from the BSP. So + * the BSP NMI handler saves current context, does some fixups and makes + * the hypercall to disable the hypervisor, ie, devirtualize. Hypervisor + * at that point will suspend all vcpus (except the BSP), unlock all its + * RAM, and return to Linux at the 32bit mode entry RIP. + * + * Linux 32bit entry trampoline will then restore long mode and call C + * function here to restore context and continue execution to crash kexec. + */ + +#include <linux/delay.h> +#include <linux/kexec.h> +#include <linux/crash_dump.h> +#include <linux/panic.h> +#include <asm/apic.h> +#include <asm/desc.h> +#include <asm/page.h> +#include <asm/pgalloc.h> +#include <asm/mshyperv.h> +#include <asm/nmi.h> +#include <asm/idtentry.h> +#include <asm/reboot.h> +#include <asm/intel_pt.h> + +bool hv_crash_enabled; +EXPORT_SYMBOL_GPL(hv_crash_enabled); + +struct hv_crash_ctxt { + ulong rsp; + ulong cr0; + ulong cr2; + ulong cr4; + ulong cr8; + + u16 cs; + u16 ss; + u16 ds; + u16 es; + u16 fs; + u16 gs; + + u16 gdt_fill; + struct desc_ptr gdtr; + char idt_fill[6]; + struct desc_ptr idtr; + + u64 gsbase; + u64 efer; + u64 pat; +}; +static struct hv_crash_ctxt hv_crash_ctxt; + +/* Shared hypervisor page that contains crash dump area we peek into. + * NB: windbg looks for "hv_cda" symbol so don't change it. + */ +static struct hv_crashdump_area *hv_cda; + +static u32 trampoline_pa, devirt_arg; +static atomic_t crash_cpus_wait; +static void *hv_crash_ptpgs[4]; +static bool hv_has_crashed, lx_has_crashed; + +static void __noreturn hv_panic_timeout_reboot(void) +{ + #define PANIC_TIMER_STEP 100 + + if (panic_timeout > 0) { + int i; + + for (i = 0; i < panic_timeout * 1000; i += PANIC_TIMER_STEP) + mdelay(PANIC_TIMER_STEP); + } + + if (panic_timeout) + native_wrmsrq(HV_X64_MSR_RESET, 1); /* get hyp to reboot */ + + for (;;) + cpu_relax(); +} + +/* This cannot be inlined as it needs stack */ +static noinline __noclone void hv_crash_restore_tss(void) +{ + load_TR_desc(); +} + +/* This cannot be inlined as it needs stack */ +static noinline void hv_crash_clear_kernpt(void) +{ + pgd_t *pgd; + p4d_t *p4d; + + /* Clear entry so it's not confusing to someone looking at the core */ + pgd = pgd_offset_k(trampoline_pa); + p4d = p4d_offset(pgd, trampoline_pa); + native_p4d_clear(p4d); +} + +/* + * This is the C entry point from the asm glue code after the disable hypercall. + * We enter here in IA32-e long mode, ie, full 64bit mode running on kernel + * page tables with our below 4G page identity mapped, but using a temporary + * GDT. ds/fs/gs/es are null. ss is not usable. bp is null. stack is not + * available. We restore kernel GDT, and rest of the context, and continue + * to kexec. + */ +static asmlinkage void __noreturn hv_crash_c_entry(void) +{ + struct hv_crash_ctxt *ctxt = &hv_crash_ctxt; + + /* first thing, restore kernel gdt */ + native_load_gdt(&ctxt->gdtr); + + asm volatile("movw %%ax, %%ss" : : "a"(ctxt->ss)); + asm volatile("movq %0, %%rsp" : : "m"(ctxt->rsp)); + + asm volatile("movw %%ax, %%ds" : : "a"(ctxt->ds)); + asm volatile("movw %%ax, %%es" : : "a"(ctxt->es)); + asm volatile("movw %%ax, %%fs" : : "a"(ctxt->fs)); + asm volatile("movw %%ax, %%gs" : : "a"(ctxt->gs)); + + native_wrmsrq(MSR_IA32_CR_PAT, ctxt->pat); + asm volatile("movq %0, %%cr0" : : "r"(ctxt->cr0)); + + asm volatile("movq %0, %%cr8" : : "r"(ctxt->cr8)); + asm volatile("movq %0, %%cr4" : : "r"(ctxt->cr4)); + asm volatile("movq %0, %%cr2" : : "r"(ctxt->cr4)); + + native_load_idt(&ctxt->idtr); + native_wrmsrq(MSR_GS_BASE, ctxt->gsbase); + native_wrmsrq(MSR_EFER, ctxt->efer); + + /* restore the original kernel CS now via far return */ + asm volatile("movzwq %0, %%rax\n\t" + "pushq %%rax\n\t" + "pushq $1f\n\t" + "lretq\n\t" + "1:nop\n\t" : : "m"(ctxt->cs) : "rax"); + + /* We are in asmlinkage without stack frame, hence make C function + * calls which will buy stack frames. + */ + hv_crash_restore_tss(); + hv_crash_clear_kernpt(); + + /* we are now fully in devirtualized normal kernel mode */ + __crash_kexec(NULL); + + hv_panic_timeout_reboot(); +} +/* Tell gcc we are using lretq long jump in the above function intentionally */ +STACK_FRAME_NON_STANDARD(hv_crash_c_entry); + +static void hv_mark_tss_not_busy(void) +{ + struct desc_struct *desc = get_current_gdt_rw(); + tss_desc tss; + + memcpy(&tss, &desc[GDT_ENTRY_TSS], sizeof(tss_desc)); + tss.type = 0x9; /* available 64-bit TSS. 0xB is busy TSS */ + write_gdt_entry(desc, GDT_ENTRY_TSS, &tss, DESC_TSS); +} + +/* Save essential context */ +static void hv_hvcrash_ctxt_save(void) +{ + struct hv_crash_ctxt *ctxt = &hv_crash_ctxt; + + asm volatile("movq %%rsp,%0" : "=m"(ctxt->rsp)); + + ctxt->cr0 = native_read_cr0(); + ctxt->cr4 = native_read_cr4(); + + asm volatile("movq %%cr2, %0" : "=a"(ctxt->cr2)); + asm volatile("movq %%cr8, %0" : "=a"(ctxt->cr8)); + + asm volatile("movl %%cs, %%eax" : "=a"(ctxt->cs)); + asm volatile("movl %%ss, %%eax" : "=a"(ctxt->ss)); + asm volatile("movl %%ds, %%eax" : "=a"(ctxt->ds)); + asm volatile("movl %%es, %%eax" : "=a"(ctxt->es)); + asm volatile("movl %%fs, %%eax" : "=a"(ctxt->fs)); + asm volatile("movl %%gs, %%eax" : "=a"(ctxt->gs)); + + native_store_gdt(&ctxt->gdtr); + store_idt(&ctxt->idtr); + + ctxt->gsbase = __rdmsr(MSR_GS_BASE); + ctxt->efer = __rdmsr(MSR_EFER); + ctxt->pat = __rdmsr(MSR_IA32_CR_PAT); +} + +/* Add trampoline page to the kernel pagetable for transition to kernel PT */ +static void hv_crash_fixup_kernpt(void) +{ + pgd_t *pgd; + p4d_t *p4d; + + pgd = pgd_offset_k(trampoline_pa); + p4d = p4d_offset(pgd, trampoline_pa); + + /* trampoline_pa is below 4G, so no pre-existing entry to clobber */ + p4d_populate(&init_mm, p4d, (pud_t *)hv_crash_ptpgs[1]); + p4d->p4d = p4d->p4d & ~(_PAGE_NX); /* enable execute */ +} + +/* + * Notify the hyp that Linux has crashed. This will cause the hyp to quiesce + * and suspend all guest VPs. + */ +static void hv_notify_prepare_hyp(void) +{ + u64 status; + struct hv_input_notify_partition_event *input; + struct hv_partition_event_root_crashdump_input *cda; + + input = *this_cpu_ptr(hyperv_pcpu_input_arg); + cda = &input->input.crashdump_input; + memset(input, 0, sizeof(*input)); + input->event = HV_PARTITION_EVENT_ROOT_CRASHDUMP; + + cda->crashdump_action = HV_CRASHDUMP_ENTRY; + status = hv_do_hypercall(HVCALL_NOTIFY_PARTITION_EVENT, input, NULL); + if (!hv_result_success(status)) + return; + + cda->crashdump_action = HV_CRASHDUMP_SUSPEND_ALL_VPS; + hv_do_hypercall(HVCALL_NOTIFY_PARTITION_EVENT, input, NULL); +} + +/* + * Common function for all cpus before devirtualization. + * + * Hypervisor crash: all cpus get here in NMI context. + * Linux crash: the panicing cpu gets here at base level, all others in NMI + * context. Note, panicing cpu may not be the BSP. + * + * The function is not inlined so it will show on the stack. It is named so + * because the crash cmd looks for certain well known function names on the + * stack before looking into the cpu saved note in the elf section, and + * that work is currently incomplete. + * + * Notes: + * Hypervisor crash: + * - the hypervisor is in a very restrictive mode at this point and any + * vmexit it cannot handle would result in reboot. So, no mumbo jumbo, + * just get to kexec as quickly as possible. + * + * Devirtualization is supported from the BSP only at present. + */ +static noinline __noclone void crash_nmi_callback(struct pt_regs *regs) +{ + struct hv_input_disable_hyp_ex *input; + u64 status; + int msecs = 1000, ccpu = smp_processor_id(); + + if (ccpu == 0) { + /* crash_save_cpu() will be done in the kexec path */ + cpu_emergency_stop_pt(); /* disable performance trace */ + atomic_inc(&crash_cpus_wait); + } else { + crash_save_cpu(regs, ccpu); + cpu_emergency_stop_pt(); /* disable performance trace */ + atomic_inc(&crash_cpus_wait); + for (;;) + cpu_relax(); + } + + while (atomic_read(&crash_cpus_wait) < num_online_cpus() && msecs--) + mdelay(1); + + stop_nmi(); + if (!hv_has_crashed) + hv_notify_prepare_hyp(); + + if (crashing_cpu == -1) + crashing_cpu = ccpu; /* crash cmd uses this */ + + hv_hvcrash_ctxt_save(); + hv_mark_tss_not_busy(); + hv_crash_fixup_kernpt(); + + input = *this_cpu_ptr(hyperv_pcpu_input_arg); + memset(input, 0, sizeof(*input)); + input->rip = trampoline_pa; + input->arg = devirt_arg; + + status = hv_do_hypercall(HVCALL_DISABLE_HYP_EX, input, NULL); + + hv_panic_timeout_reboot(); +} + + +static DEFINE_SPINLOCK(hv_crash_reboot_lk); + +/* + * Generic NMI callback handler: could be called without any crash also. + * hv crash: hypervisor injects NMI's into all cpus + * lx crash: panicing cpu sends NMI to all but self via crash_stop_other_cpus + */ +static int hv_crash_nmi_local(unsigned int cmd, struct pt_regs *regs) +{ + if (!hv_has_crashed && hv_cda && hv_cda->cda_valid) + hv_has_crashed = true; + + if (!hv_has_crashed && !lx_has_crashed) + return NMI_DONE; /* ignore the NMI */ + + if (hv_has_crashed && !kexec_crash_loaded()) { + if (spin_trylock(&hv_crash_reboot_lk)) + hv_panic_timeout_reboot(); + else + for (;;) + cpu_relax(); + } + + crash_nmi_callback(regs); + + return NMI_DONE; +} + +/* + * hv_crash_stop_other_cpus() == smp_ops.crash_stop_other_cpus + * + * On normal Linux panic, this is called twice: first from panic and then again + * from native_machine_crash_shutdown. + * + * In case of hyperv, 3 ways to get here: + * 1. hv crash (only BSP will get here): + * BSP : NMI callback -> DisableHv -> hv_crash_asm32 -> hv_crash_c_entry + * -> __crash_kexec -> native_machine_crash_shutdown + * -> crash_smp_send_stop -> smp_ops.crash_stop_other_cpus + * Linux panic: + * 2. panic cpu x: panic() -> crash_smp_send_stop + * -> smp_ops.crash_stop_other_cpus + * 3. BSP: native_machine_crash_shutdown -> crash_smp_send_stop + * + * NB: noclone and non standard stack because of call to crash_setup_regs(). + */ +static void __noclone hv_crash_stop_other_cpus(void) +{ + static bool crash_stop_done; + struct pt_regs lregs; + int ccpu = smp_processor_id(); + + if (hv_has_crashed) + return; /* all cpus already in NMI handler path */ + + if (!kexec_crash_loaded()) { + hv_notify_prepare_hyp(); + hv_panic_timeout_reboot(); /* no return */ + } + + /* If the hv crashes also, we could come here again before cpus_stopped + * is set in crash_smp_send_stop(). So use our own check. + */ + if (crash_stop_done) + return; + crash_stop_done = true; + + /* Linux has crashed: hv is healthy, we can IPI safely */ + lx_has_crashed = true; + wmb(); /* NMI handlers look at lx_has_crashed */ + + apic->send_IPI_allbutself(NMI_VECTOR); + + if (crashing_cpu == -1) + crashing_cpu = ccpu; /* crash cmd uses this */ + + /* crash_setup_regs() happens in kexec also, but for the kexec cpu which + * is the BSP. We could be here on non-BSP cpu, collect regs if so. + */ + if (ccpu) + crash_setup_regs(&lregs, NULL); + + crash_nmi_callback(&lregs); +} +STACK_FRAME_NON_STANDARD(hv_crash_stop_other_cpus); + +/* This GDT is accessed in IA32-e compat mode which uses 32bits addresses */ +struct hv_gdtreg_32 { + u16 fill; + u16 limit; + u32 address; +} __packed; + +/* We need a CS with L bit to goto IA32-e long mode from 32bit compat mode */ +struct hv_crash_tramp_gdt { + u64 null; /* index 0, selector 0, null selector */ + u64 cs64; /* index 1, selector 8, cs64 selector */ +} __packed; + +/* No stack, so jump via far ptr in memory to load the 64bit CS */ +struct hv_cs_jmptgt { + u32 address; + u16 csval; + u16 fill; +} __packed; + +/* Linux use only, hypervisor doesn't look at this struct */ +struct hv_crash_tramp_data { + u64 tramp32_cr3; + u64 kernel_cr3; + struct hv_gdtreg_32 gdtr32; + struct hv_crash_tramp_gdt tramp_gdt; + struct hv_cs_jmptgt cs_jmptgt; + u64 c_entry_addr; +} __packed; + +/* + * Setup a temporary gdt to allow the asm code to switch to the long mode. + * Since the asm code is relocated/copied to a below 4G page, it cannot use rip + * relative addressing, hence we must use trampoline_pa here. Also, save other + * info like jmp and C entry targets for same reasons. + * + * Returns: 0 on success, -1 on error + */ +static int hv_crash_setup_trampdata(u64 trampoline_va) +{ + int size, offs; + void *dest; + struct hv_crash_tramp_data *tramp; + + /* These must match exactly the ones in the corresponding asm file */ + BUILD_BUG_ON(offsetof(struct hv_crash_tramp_data, tramp32_cr3) != 0); + BUILD_BUG_ON(offsetof(struct hv_crash_tramp_data, kernel_cr3) != 8); + BUILD_BUG_ON(offsetof(struct hv_crash_tramp_data, gdtr32.limit) != 18); + BUILD_BUG_ON(offsetof(struct hv_crash_tramp_data, + cs_jmptgt.address) != 40); + BUILD_BUG_ON(offsetof(struct hv_crash_tramp_data, c_entry_addr) != 48); + + /* hv_crash_asm_end is beyond last byte by 1 */ + size = &hv_crash_asm_end - &hv_crash_asm32; + if (size + sizeof(struct hv_crash_tramp_data) > PAGE_SIZE) { + pr_err("%s: trampoline page overflow\n", __func__); + return -1; + } + + dest = (void *)trampoline_va; + memcpy(dest, &hv_crash_asm32, size); + + dest += size; + dest = (void *)round_up((ulong)dest, 16); + tramp = (struct hv_crash_tramp_data *)dest; + + /* see MAX_ASID_AVAILABLE in tlb.c: "PCID 0 is reserved for use by + * non-PCID-aware users". Build cr3 with pcid 0 + */ + tramp->tramp32_cr3 = __sme_pa(hv_crash_ptpgs[0]); + + /* Note, when restoring X86_CR4_PCIDE, cr3[11:0] must be zero */ + tramp->kernel_cr3 = __sme_pa(init_mm.pgd); + + tramp->gdtr32.limit = sizeof(struct hv_crash_tramp_gdt); + tramp->gdtr32.address = trampoline_pa + + (ulong)&tramp->tramp_gdt - trampoline_va; + + /* base:0 limit:0xfffff type:b dpl:0 P:1 L:1 D:0 avl:0 G:1 */ + tramp->tramp_gdt.cs64 = 0x00af9a000000ffff; + + tramp->cs_jmptgt.csval = 0x8; + offs = (ulong)&hv_crash_asm64 - (ulong)&hv_crash_asm32; + tramp->cs_jmptgt.address = trampoline_pa + offs; + + tramp->c_entry_addr = (u64)&hv_crash_c_entry; + + devirt_arg = trampoline_pa + (ulong)dest - trampoline_va; + + return 0; +} + +/* + * Build 32bit trampoline page table for transition from protected mode + * non-paging to long-mode paging. This transition needs pagetables below 4G. + */ +static void hv_crash_build_tramp_pt(void) +{ + p4d_t *p4d; + pud_t *pud; + pmd_t *pmd; + pte_t *pte; + u64 pa, addr = trampoline_pa; + + p4d = hv_crash_ptpgs[0] + pgd_index(addr) * sizeof(p4d); + pa = virt_to_phys(hv_crash_ptpgs[1]); + set_p4d(p4d, __p4d(_PAGE_TABLE | pa)); + p4d->p4d &= ~(_PAGE_NX); /* enable execute */ + + pud = hv_crash_ptpgs[1] + pud_index(addr) * sizeof(pud); + pa = virt_to_phys(hv_crash_ptpgs[2]); + set_pud(pud, __pud(_PAGE_TABLE | pa)); + + pmd = hv_crash_ptpgs[2] + pmd_index(addr) * sizeof(pmd); + pa = virt_to_phys(hv_crash_ptpgs[3]); + set_pmd(pmd, __pmd(_PAGE_TABLE | pa)); + + pte = hv_crash_ptpgs[3] + pte_index(addr) * sizeof(pte); + set_pte(pte, pfn_pte(addr >> PAGE_SHIFT, PAGE_KERNEL_EXEC)); +} + +/* + * Setup trampoline for devirtualization: + * - a page below 4G, ie 32bit addr containing asm glue code that hyp jmps to + * in protected mode. + * - 4 pages for a temporary page table that asm code uses to turn paging on + * - a temporary gdt to use in the compat mode. + * + * Returns: 0 on success + */ +static int hv_crash_trampoline_setup(void) +{ + int i, rc, order; + struct page *page; + u64 trampoline_va; + gfp_t flags32 = GFP_KERNEL | GFP_DMA32 | __GFP_ZERO; + + /* page for 32bit trampoline assembly code + hv_crash_tramp_data */ + page = alloc_page(flags32); + if (page == NULL) { + pr_err("%s: failed to alloc asm stub page\n", __func__); + return -1; + } + + trampoline_va = (u64)page_to_virt(page); + trampoline_pa = (u32)page_to_phys(page); + + order = 2; /* alloc 2^2 pages */ + page = alloc_pages(flags32, order); + if (page == NULL) { + pr_err("%s: failed to alloc pt pages\n", __func__); + free_page(trampoline_va); + return -1; + } + + for (i = 0; i < 4; i++, page++) + hv_crash_ptpgs[i] = page_to_virt(page); + + hv_crash_build_tramp_pt(); + + rc = hv_crash_setup_trampdata(trampoline_va); + if (rc) + goto errout; + + return 0; + +errout: + free_page(trampoline_va); + free_pages((ulong)hv_crash_ptpgs[0], order); + + return rc; +} + +/* Setup for kdump kexec to collect hypervisor RAM when running as root */ +void hv_root_crash_init(void) +{ + int rc; + struct hv_input_get_system_property *input; + struct hv_output_get_system_property *output; + unsigned long flags; + u64 status; + union hv_pfn_range cda_info; + + if (pgtable_l5_enabled()) { + pr_err("Hyper-V: crash dump not yet supported on 5level PTs\n"); + return; + } + + rc = register_nmi_handler(NMI_LOCAL, hv_crash_nmi_local, NMI_FLAG_FIRST, + "hv_crash_nmi"); + if (rc) { + pr_err("Hyper-V: failed to register crash nmi handler\n"); + return; + } + + local_irq_save(flags); + input = *this_cpu_ptr(hyperv_pcpu_input_arg); + output = *this_cpu_ptr(hyperv_pcpu_output_arg); + + memset(input, 0, sizeof(*input)); + input->property_id = HV_SYSTEM_PROPERTY_CRASHDUMPAREA; + + status = hv_do_hypercall(HVCALL_GET_SYSTEM_PROPERTY, input, output); + cda_info.as_uint64 = output->hv_cda_info.as_uint64; + local_irq_restore(flags); + + if (!hv_result_success(status)) { + pr_err("Hyper-V: %s: property:%d %s\n", __func__, + input->property_id, hv_result_to_string(status)); + goto err_out; + } + + if (cda_info.base_pfn == 0) { + pr_err("Hyper-V: hypervisor crash dump area pfn is 0\n"); + goto err_out; + } + + hv_cda = phys_to_virt(cda_info.base_pfn << HV_HYP_PAGE_SHIFT); + + rc = hv_crash_trampoline_setup(); + if (rc) + goto err_out; + + smp_ops.crash_stop_other_cpus = hv_crash_stop_other_cpus; + + crash_kexec_post_notifiers = true; + hv_crash_enabled = true; + pr_info("Hyper-V: both linux and hypervisor kdump support enabled\n"); + + return; + +err_out: + unregister_nmi_handler(NMI_LOCAL, "hv_crash_nmi"); + pr_err("Hyper-V: only linux root kdump support enabled\n"); +} |