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-rw-r--r--arch/x86/kernel/fpu/core.c523
1 files changed, 523 insertions, 0 deletions
diff --git a/arch/x86/kernel/fpu/core.c b/arch/x86/kernel/fpu/core.c
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+++ b/arch/x86/kernel/fpu/core.c
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+/*
+ * Copyright (C) 1994 Linus Torvalds
+ *
+ * Pentium III FXSR, SSE support
+ * General FPU state handling cleanups
+ * Gareth Hughes <gareth@valinux.com>, May 2000
+ */
+#include <asm/fpu/internal.h>
+#include <asm/fpu/regset.h>
+#include <asm/fpu/signal.h>
+#include <asm/traps.h>
+
+#include <linux/hardirq.h>
+
+/*
+ * Represents the initial FPU state. It's mostly (but not completely) zeroes,
+ * depending on the FPU hardware format:
+ */
+union fpregs_state init_fpstate __read_mostly;
+
+/*
+ * Track whether the kernel is using the FPU state
+ * currently.
+ *
+ * This flag is used:
+ *
+ * - by IRQ context code to potentially use the FPU
+ * if it's unused.
+ *
+ * - to debug kernel_fpu_begin()/end() correctness
+ */
+static DEFINE_PER_CPU(bool, in_kernel_fpu);
+
+/*
+ * Track which context is using the FPU on the CPU:
+ */
+DEFINE_PER_CPU(struct fpu *, fpu_fpregs_owner_ctx);
+
+static void kernel_fpu_disable(void)
+{
+ WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
+ this_cpu_write(in_kernel_fpu, true);
+}
+
+static void kernel_fpu_enable(void)
+{
+ WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
+ this_cpu_write(in_kernel_fpu, false);
+}
+
+static bool kernel_fpu_disabled(void)
+{
+ return this_cpu_read(in_kernel_fpu);
+}
+
+/*
+ * Were we in an interrupt that interrupted kernel mode?
+ *
+ * On others, we can do a kernel_fpu_begin/end() pair *ONLY* if that
+ * pair does nothing at all: the thread must not have fpu (so
+ * that we don't try to save the FPU state), and TS must
+ * be set (so that the clts/stts pair does nothing that is
+ * visible in the interrupted kernel thread).
+ *
+ * Except for the eagerfpu case when we return true; in the likely case
+ * the thread has FPU but we are not going to set/clear TS.
+ */
+static bool interrupted_kernel_fpu_idle(void)
+{
+ if (kernel_fpu_disabled())
+ return false;
+
+ if (use_eager_fpu())
+ return true;
+
+ return !current->thread.fpu.fpregs_active && (read_cr0() & X86_CR0_TS);
+}
+
+/*
+ * Were we in user mode (or vm86 mode) when we were
+ * interrupted?
+ *
+ * Doing kernel_fpu_begin/end() is ok if we are running
+ * in an interrupt context from user mode - we'll just
+ * save the FPU state as required.
+ */
+static bool interrupted_user_mode(void)
+{
+ struct pt_regs *regs = get_irq_regs();
+ return regs && user_mode(regs);
+}
+
+/*
+ * Can we use the FPU in kernel mode with the
+ * whole "kernel_fpu_begin/end()" sequence?
+ *
+ * It's always ok in process context (ie "not interrupt")
+ * but it is sometimes ok even from an irq.
+ */
+bool irq_fpu_usable(void)
+{
+ return !in_interrupt() ||
+ interrupted_user_mode() ||
+ interrupted_kernel_fpu_idle();
+}
+EXPORT_SYMBOL(irq_fpu_usable);
+
+void __kernel_fpu_begin(void)
+{
+ struct fpu *fpu = &current->thread.fpu;
+
+ WARN_ON_FPU(!irq_fpu_usable());
+
+ kernel_fpu_disable();
+
+ if (fpu->fpregs_active) {
+ copy_fpregs_to_fpstate(fpu);
+ } else {
+ this_cpu_write(fpu_fpregs_owner_ctx, NULL);
+ __fpregs_activate_hw();
+ }
+}
+EXPORT_SYMBOL(__kernel_fpu_begin);
+
+void __kernel_fpu_end(void)
+{
+ struct fpu *fpu = &current->thread.fpu;
+
+ if (fpu->fpregs_active)
+ copy_kernel_to_fpregs(&fpu->state);
+ else
+ __fpregs_deactivate_hw();
+
+ kernel_fpu_enable();
+}
+EXPORT_SYMBOL(__kernel_fpu_end);
+
+void kernel_fpu_begin(void)
+{
+ preempt_disable();
+ __kernel_fpu_begin();
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_begin);
+
+void kernel_fpu_end(void)
+{
+ __kernel_fpu_end();
+ preempt_enable();
+}
+EXPORT_SYMBOL_GPL(kernel_fpu_end);
+
+/*
+ * CR0::TS save/restore functions:
+ */
+int irq_ts_save(void)
+{
+ /*
+ * If in process context and not atomic, we can take a spurious DNA fault.
+ * Otherwise, doing clts() in process context requires disabling preemption
+ * or some heavy lifting like kernel_fpu_begin()
+ */
+ if (!in_atomic())
+ return 0;
+
+ if (read_cr0() & X86_CR0_TS) {
+ clts();
+ return 1;
+ }
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(irq_ts_save);
+
+void irq_ts_restore(int TS_state)
+{
+ if (TS_state)
+ stts();
+}
+EXPORT_SYMBOL_GPL(irq_ts_restore);
+
+/*
+ * Save the FPU state (mark it for reload if necessary):
+ *
+ * This only ever gets called for the current task.
+ */
+void fpu__save(struct fpu *fpu)
+{
+ WARN_ON_FPU(fpu != &current->thread.fpu);
+
+ preempt_disable();
+ if (fpu->fpregs_active) {
+ if (!copy_fpregs_to_fpstate(fpu))
+ fpregs_deactivate(fpu);
+ }
+ preempt_enable();
+}
+EXPORT_SYMBOL_GPL(fpu__save);
+
+/*
+ * Legacy x87 fpstate state init:
+ */
+static inline void fpstate_init_fstate(struct fregs_state *fp)
+{
+ fp->cwd = 0xffff037fu;
+ fp->swd = 0xffff0000u;
+ fp->twd = 0xffffffffu;
+ fp->fos = 0xffff0000u;
+}
+
+void fpstate_init(union fpregs_state *state)
+{
+ if (!cpu_has_fpu) {
+ fpstate_init_soft(&state->soft);
+ return;
+ }
+
+ memset(state, 0, xstate_size);
+
+ if (cpu_has_fxsr)
+ fpstate_init_fxstate(&state->fxsave);
+ else
+ fpstate_init_fstate(&state->fsave);
+}
+EXPORT_SYMBOL_GPL(fpstate_init);
+
+/*
+ * Copy the current task's FPU state to a new task's FPU context.
+ *
+ * In both the 'eager' and the 'lazy' case we save hardware registers
+ * directly to the destination buffer.
+ */
+static void fpu_copy(struct fpu *dst_fpu, struct fpu *src_fpu)
+{
+ WARN_ON_FPU(src_fpu != &current->thread.fpu);
+
+ /*
+ * Don't let 'init optimized' areas of the XSAVE area
+ * leak into the child task:
+ */
+ if (use_eager_fpu())
+ memset(&dst_fpu->state.xsave, 0, xstate_size);
+
+ /*
+ * Save current FPU registers directly into the child
+ * FPU context, without any memory-to-memory copying.
+ *
+ * If the FPU context got destroyed in the process (FNSAVE
+ * done on old CPUs) then copy it back into the source
+ * context and mark the current task for lazy restore.
+ *
+ * We have to do all this with preemption disabled,
+ * mostly because of the FNSAVE case, because in that
+ * case we must not allow preemption in the window
+ * between the FNSAVE and us marking the context lazy.
+ *
+ * It shouldn't be an issue as even FNSAVE is plenty
+ * fast in terms of critical section length.
+ */
+ preempt_disable();
+ if (!copy_fpregs_to_fpstate(dst_fpu)) {
+ memcpy(&src_fpu->state, &dst_fpu->state, xstate_size);
+ fpregs_deactivate(src_fpu);
+ }
+ preempt_enable();
+}
+
+int fpu__copy(struct fpu *dst_fpu, struct fpu *src_fpu)
+{
+ dst_fpu->counter = 0;
+ dst_fpu->fpregs_active = 0;
+ dst_fpu->last_cpu = -1;
+
+ if (src_fpu->fpstate_active)
+ fpu_copy(dst_fpu, src_fpu);
+
+ return 0;
+}
+
+/*
+ * Activate the current task's in-memory FPU context,
+ * if it has not been used before:
+ */
+void fpu__activate_curr(struct fpu *fpu)
+{
+ WARN_ON_FPU(fpu != &current->thread.fpu);
+
+ if (!fpu->fpstate_active) {
+ fpstate_init(&fpu->state);
+
+ /* Safe to do for the current task: */
+ fpu->fpstate_active = 1;
+ }
+}
+EXPORT_SYMBOL_GPL(fpu__activate_curr);
+
+/*
+ * This function must be called before we read a task's fpstate.
+ *
+ * If the task has not used the FPU before then initialize its
+ * fpstate.
+ *
+ * If the task has used the FPU before then save it.
+ */
+void fpu__activate_fpstate_read(struct fpu *fpu)
+{
+ /*
+ * If fpregs are active (in the current CPU), then
+ * copy them to the fpstate:
+ */
+ if (fpu->fpregs_active) {
+ fpu__save(fpu);
+ } else {
+ if (!fpu->fpstate_active) {
+ fpstate_init(&fpu->state);
+
+ /* Safe to do for current and for stopped child tasks: */
+ fpu->fpstate_active = 1;
+ }
+ }
+}
+
+/*
+ * This function must be called before we write a task's fpstate.
+ *
+ * If the task has used the FPU before then unlazy it.
+ * If the task has not used the FPU before then initialize its fpstate.
+ *
+ * After this function call, after registers in the fpstate are
+ * modified and the child task has woken up, the child task will
+ * restore the modified FPU state from the modified context. If we
+ * didn't clear its lazy status here then the lazy in-registers
+ * state pending on its former CPU could be restored, corrupting
+ * the modifications.
+ */
+void fpu__activate_fpstate_write(struct fpu *fpu)
+{
+ /*
+ * Only stopped child tasks can be used to modify the FPU
+ * state in the fpstate buffer:
+ */
+ WARN_ON_FPU(fpu == &current->thread.fpu);
+
+ if (fpu->fpstate_active) {
+ /* Invalidate any lazy state: */
+ fpu->last_cpu = -1;
+ } else {
+ fpstate_init(&fpu->state);
+
+ /* Safe to do for stopped child tasks: */
+ fpu->fpstate_active = 1;
+ }
+}
+
+/*
+ * 'fpu__restore()' is called to copy FPU registers from
+ * the FPU fpstate to the live hw registers and to activate
+ * access to the hardware registers, so that FPU instructions
+ * can be used afterwards.
+ *
+ * Must be called with kernel preemption disabled (for example
+ * with local interrupts disabled, as it is in the case of
+ * do_device_not_available()).
+ */
+void fpu__restore(struct fpu *fpu)
+{
+ fpu__activate_curr(fpu);
+
+ /* Avoid __kernel_fpu_begin() right after fpregs_activate() */
+ kernel_fpu_disable();
+ fpregs_activate(fpu);
+ copy_kernel_to_fpregs(&fpu->state);
+ fpu->counter++;
+ kernel_fpu_enable();
+}
+EXPORT_SYMBOL_GPL(fpu__restore);
+
+/*
+ * Drops current FPU state: deactivates the fpregs and
+ * the fpstate. NOTE: it still leaves previous contents
+ * in the fpregs in the eager-FPU case.
+ *
+ * This function can be used in cases where we know that
+ * a state-restore is coming: either an explicit one,
+ * or a reschedule.
+ */
+void fpu__drop(struct fpu *fpu)
+{
+ preempt_disable();
+ fpu->counter = 0;
+
+ if (fpu->fpregs_active) {
+ /* Ignore delayed exceptions from user space */
+ asm volatile("1: fwait\n"
+ "2:\n"
+ _ASM_EXTABLE(1b, 2b));
+ fpregs_deactivate(fpu);
+ }
+
+ fpu->fpstate_active = 0;
+
+ preempt_enable();
+}
+
+/*
+ * Clear FPU registers by setting them up from
+ * the init fpstate:
+ */
+static inline void copy_init_fpstate_to_fpregs(void)
+{
+ if (use_xsave())
+ copy_kernel_to_xregs(&init_fpstate.xsave, -1);
+ else
+ copy_kernel_to_fxregs(&init_fpstate.fxsave);
+}
+
+/*
+ * Clear the FPU state back to init state.
+ *
+ * Called by sys_execve(), by the signal handler code and by various
+ * error paths.
+ */
+void fpu__clear(struct fpu *fpu)
+{
+ WARN_ON_FPU(fpu != &current->thread.fpu); /* Almost certainly an anomaly */
+
+ if (!use_eager_fpu()) {
+ /* FPU state will be reallocated lazily at the first use. */
+ fpu__drop(fpu);
+ } else {
+ if (!fpu->fpstate_active) {
+ fpu__activate_curr(fpu);
+ user_fpu_begin();
+ }
+ copy_init_fpstate_to_fpregs();
+ }
+}
+
+/*
+ * x87 math exception handling:
+ */
+
+static inline unsigned short get_fpu_cwd(struct fpu *fpu)
+{
+ if (cpu_has_fxsr) {
+ return fpu->state.fxsave.cwd;
+ } else {
+ return (unsigned short)fpu->state.fsave.cwd;
+ }
+}
+
+static inline unsigned short get_fpu_swd(struct fpu *fpu)
+{
+ if (cpu_has_fxsr) {
+ return fpu->state.fxsave.swd;
+ } else {
+ return (unsigned short)fpu->state.fsave.swd;
+ }
+}
+
+static inline unsigned short get_fpu_mxcsr(struct fpu *fpu)
+{
+ if (cpu_has_xmm) {
+ return fpu->state.fxsave.mxcsr;
+ } else {
+ return MXCSR_DEFAULT;
+ }
+}
+
+int fpu__exception_code(struct fpu *fpu, int trap_nr)
+{
+ int err;
+
+ if (trap_nr == X86_TRAP_MF) {
+ unsigned short cwd, swd;
+ /*
+ * (~cwd & swd) will mask out exceptions that are not set to unmasked
+ * status. 0x3f is the exception bits in these regs, 0x200 is the
+ * C1 reg you need in case of a stack fault, 0x040 is the stack
+ * fault bit. We should only be taking one exception at a time,
+ * so if this combination doesn't produce any single exception,
+ * then we have a bad program that isn't synchronizing its FPU usage
+ * and it will suffer the consequences since we won't be able to
+ * fully reproduce the context of the exception
+ */
+ cwd = get_fpu_cwd(fpu);
+ swd = get_fpu_swd(fpu);
+
+ err = swd & ~cwd;
+ } else {
+ /*
+ * The SIMD FPU exceptions are handled a little differently, as there
+ * is only a single status/control register. Thus, to determine which
+ * unmasked exception was caught we must mask the exception mask bits
+ * at 0x1f80, and then use these to mask the exception bits at 0x3f.
+ */
+ unsigned short mxcsr = get_fpu_mxcsr(fpu);
+ err = ~(mxcsr >> 7) & mxcsr;
+ }
+
+ if (err & 0x001) { /* Invalid op */
+ /*
+ * swd & 0x240 == 0x040: Stack Underflow
+ * swd & 0x240 == 0x240: Stack Overflow
+ * User must clear the SF bit (0x40) if set
+ */
+ return FPE_FLTINV;
+ } else if (err & 0x004) { /* Divide by Zero */
+ return FPE_FLTDIV;
+ } else if (err & 0x008) { /* Overflow */
+ return FPE_FLTOVF;
+ } else if (err & 0x012) { /* Denormal, Underflow */
+ return FPE_FLTUND;
+ } else if (err & 0x020) { /* Precision */
+ return FPE_FLTRES;
+ }
+
+ /*
+ * If we're using IRQ 13, or supposedly even some trap
+ * X86_TRAP_MF implementations, it's possible
+ * we get a spurious trap, which is not an error.
+ */
+ return 0;
+}