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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 = ¤t->thread.fpu;
WARN_ON_FPU(!irq_fpu_usable());
kernel_fpu_disable();
if (fpu->fpregs_active) {
/*
* Ignore return value -- we don't care if reg state
* is clobbered.
*/
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 = ¤t->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 != ¤t->thread.fpu);
preempt_disable();
if (fpu->fpregs_active) {
if (!copy_fpregs_to_fpstate(fpu)) {
if (use_eager_fpu())
copy_kernel_to_fpregs(&fpu->state);
else
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 (!static_cpu_has(X86_FEATURE_FPU)) {
fpstate_init_soft(&state->soft);
return;
}
memset(state, 0, xstate_size);
if (static_cpu_has(X86_FEATURE_FXSR))
fpstate_init_fxstate(&state->fxsave);
else
fpstate_init_fstate(&state->fsave);
}
EXPORT_SYMBOL_GPL(fpstate_init);
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 || !static_cpu_has(X86_FEATURE_FPU))
return 0;
WARN_ON_FPU(src_fpu != ¤t->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.
* In lazy mode, if the FPU context isn't loaded into
* fpregs, CR0.TS will be set and do_device_not_available
* will load the FPU context.
*
* 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);
if (use_eager_fpu())
copy_kernel_to_fpregs(&src_fpu->state);
else
fpregs_deactivate(src_fpu);
}
preempt_enable();
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 != ¤t->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 == ¤t->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;
}
}
/*
* This function must be called before we write the current
* task's fpstate.
*
* This call gets the current FPU register state and moves
* it in to the 'fpstate'. Preemption is disabled so that
* no writes to the 'fpstate' can occur from context
* swiches.
*
* Must be followed by a fpu__current_fpstate_write_end().
*/
void fpu__current_fpstate_write_begin(void)
{
struct fpu *fpu = ¤t->thread.fpu;
/*
* Ensure that the context-switching code does not write
* over the fpstate while we are doing our update.
*/
preempt_disable();
/*
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