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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) {
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) {
if (WARN_ON_FPU(copy_fpstate_to_fpregs(fpu)))
fpu__clear(fpu);
} 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))
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 != ¤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.
*
* 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 != ¤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) {
/* Invalidate any lazy state: */
fpu->last_cpu = -1;
} else {
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 read or write 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 and unlazy it.
*
* [ If this function is used for non-current child tasks, then
* 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.
*
* This function can be used for the current task as well, but
* only for reading the fpstate. Modifications to the fpstate
* will be lost on eagerfpu systems. ]
*
* TODO: A future optimization would be to skip the unlazying in
* the read-only case, it's not strictly necessary for
* read-only access to the context.
*/
void fpu__activate_fpstate(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) {
/* Invalidate any lazy state: */
fpu->last_cpu = -1;
} else {
fpstate_init(&fpu->state);
/* Safe to do for current and 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);
if (unlikely(copy_fpstate_to_fpregs(fpu))) {
fpu__clear(fpu);
force_sig_info(SIGSEGV, SEND_SIG_PRIV, current);
} else {
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 != ¤t->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;
}
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