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// SPDX-License-Identifier: GPL-2.0-only
/*
* 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/fpu/types.h>
#include <asm/traps.h>
#include <asm/irq_regs.h>
#include <linux/hardirq.h>
#include <linux/pkeys.h>
#define CREATE_TRACE_POINTS
#include <asm/trace/fpu.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 bool kernel_fpu_disabled(void)
{
return this_cpu_read(in_kernel_fpu);
}
static bool interrupted_kernel_fpu_idle(void)
{
return !kernel_fpu_disabled();
}
/*
* 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);
/*
* These must be called with preempt disabled. Returns
* 'true' if the FPU state is still intact and we can
* keep registers active.
*
* The legacy FNSAVE instruction cleared all FPU state
* unconditionally, so registers are essentially destroyed.
* Modern FPU state can be kept in registers, if there are
* no pending FP exceptions.
*/
int copy_fpregs_to_fpstate(struct fpu *fpu)
{
if (likely(use_xsave())) {
copy_xregs_to_kernel(&fpu->state.xsave);
/*
* AVX512 state is tracked here because its use is
* known to slow the max clock speed of the core.
*/
if (fpu->state.xsave.header.xfeatures & XFEATURE_MASK_AVX512)
fpu->avx512_timestamp = jiffies;
return 1;
}
if (likely(use_fxsr())) {
copy_fxregs_to_kernel(fpu);
return 1;
}
/*
* Legacy FPU register saving, FNSAVE always clears FPU registers,
* so we have to mark them inactive:
*/
asm volatile("fnsave %[fp]; fwait" : [fp] "=m" (fpu->state.fsave));
return 0;
}
EXPORT_SYMBOL(copy_fpregs_to_fpstate);
void kernel_fpu_begin(void)
{
preempt_disable();
WARN_ON_FPU(!irq_fpu_usable());
WARN_ON_FPU(this_cpu_read(in_kernel_fpu));
this_cpu_write(in_kernel_fpu, true);
if (!(current->flags & PF_KTHREAD) &&
!test_thread_flag(TIF_NEED_FPU_LOAD)) {
set_thread_flag(TIF_NEED_FPU_LOAD);
/*
* Ignore return value -- we don't care if reg state
* is clobbered.
*/
copy_fpregs_to_fpstate(&current->thread.fpu);
}
__cpu_invalidate_fpregs_state();
if (boot_cpu_has(X86_FEATURE_XMM))
ldmxcsr(MXCSR_DEFAULT);
if (boot_cpu_has(X86_FEATURE_FPU))
asm volatile ("fninit");
}
EXPORT_SYMBOL_GPL(kernel_fpu_begin);
void kernel_fpu_end(void)
{
WARN_ON_FPU(!this_cpu_read(in_kernel_fpu));
this_cpu_write(in_kernel_fpu, false);
preempt_enable();
}
EXPORT_SYMBOL_GPL(kernel_fpu_end);
/*
* 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);
fpregs_lock();
trace_x86_fpu_before_save(fpu);
if (!test_thread_flag(TIF_NEED_FPU_LOAD)) {
if (!copy_fpregs_to_fpstate(fpu)) {
copy_kernel_to_fpregs(&fpu->state);
}
}
trace_x86_fpu_after_save(fpu);
fpregs_unlock();
}
/*
* 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, fpu_kernel_xstate_size);
if (static_cpu_has(X86_FEATURE_XSAVES))
fpstate_init_xstate(&state->xsave);
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 task_struct *dst, struct task_struct *src)
{
struct fpu *dst_fpu = &dst->thread.fpu;
struct fpu *src_fpu = &src->thread.fpu;
dst_fpu->last_cpu = -1;
if (!static_cpu_has(X86_FEATURE_FPU))
return 0;
WARN_ON_FPU(src_fpu != &current->thread.fpu);
/*
* Don't let 'init optimized' areas of the XSAVE area
* leak into the child task:
*/
memset(&dst_fpu->state.xsave, 0, fpu_kernel_xstate_size);
/*
* If the FPU registers are not current just memcpy() the state.
* Otherwise save current FPU registers directly into the child's FPU
* context, without any memory-to-memory copying.
*
* ( The function 'fails' in the FNSAVE case, which destroys
* register contents so we have to load them back. )
*/
fpregs_lock();
if (test_thread_flag(TIF_NEED_FPU_LOAD))
memcpy(&dst_fpu->state, &src_fpu->state, fpu_kernel_xstate_size);
else if (!copy_fpregs_to_fpstate(dst_fpu))
copy_kernel_to_fpregs(&dst_fpu->state);
fpregs_unlock();
set_tsk_thread_flag(dst, TIF_NEED_FPU_LOAD);
trace_x86_fpu_copy_src(src_fpu);
trace_x86_fpu_copy_dst(dst_fpu);
return 0;
}
/*
* Activate the current task's in-memory FPU context,
* if it has not been used before:
*/
static void fpu__initialize(struct fpu *fpu)
{
WARN_ON_FPU(fpu != &current->thread.fpu);
set_thread_flag(TIF_NEED_FPU_LOAD);
fpstate_init(&fpu->state);
trace_x86_fpu_init_state(fpu);
}
/*
* This function must be called before we read a task's fpstate.
*
* There's two cases where this gets called:
*
* - for the current task (when coredumping), in which case we have
* to save the latest FPU registers into the fpstate,
*
* - or it's called for stopped tasks (ptrace), in which case the
* registers were already saved by the context-switch code when
* the task scheduled out.
*
* If the task has used the FPU before then save it.
*/
void fpu__prepare_read(struct fpu *fpu)
{
if (fpu == &current->thread.fpu)
fpu__save(fpu);
}
/*
* This function must be called before we write a task's fpstate.
*
* Invalidate any cached FPU registers.
*
* 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 cached status here then the cached in-registers
* state pending on its former CPU could be restored, corrupting
* the modifications.
*/
void fpu__prepare_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);
/* Invalidate any cached state: */
__fpu_invalidate_fpregs_state(fpu);
}
/*
* 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();
if (fpu == &current->thread.fpu) {
/* Ignore delayed exceptions from user space */
asm volatile("1: fwait\n"
"2:\n"
_ASM_EXTABLE(1b, 2b));
fpregs_deactivate(fpu);
}
trace_x86_fpu_dropped(fpu);
preempt_enable();
}
/*
* Clear FPU registers by setting them up from the init fpstate.
* Caller must do fpregs_[un]lock() around it.
*/
static inline void copy_init_fpstate_to_fpregs(u64 features_mask)
{
if (use_xsave())
copy_kernel_to_xregs(&init_fpstate.xsave, features_mask);
else if (static_cpu_has(X86_FEATURE_FXSR))
copy_kernel_to_fxregs(&init_fpstate.fxsave);
else
copy_kernel_to_fregs(&init_fpstate.fsave);
if (boot_cpu_has(X86_FEATURE_OSPKE))
copy_init_pkru_to_fpregs();
}
/*
* Clear the FPU state back to init state.
*
* Called by sys_execve(), by the signal handler code and by various
* error paths.
*/
static void fpu__clear(struct fpu *fpu, bool user_only)
{
WARN_ON_FPU(fpu != &current->thread.fpu);
if (!static_cpu_has(X86_FEATURE_FPU)) {
fpu__drop(fpu);
fpu__initialize(fpu);
return;
}
fpregs_lock();
if (user_only) {
if (!fpregs_state_valid(fpu, smp_processor_id()) &&
xfeatures_mask_supervisor())
copy_kernel_to_xregs(&fpu->state.xsave,
xfeatures_mask_supervisor());
copy_init_fpstate_to_fpregs(xfeatures_mask_user());
} else {
copy_init_fpstate_to_fpregs(xfeatures_mask_all);
}
fpregs_mark_activate();
fpregs_unlock();
}
void fpu__clear_user_states(struct fpu *fpu)
{
fpu__clear(fpu, true);
}
void fpu__clear_all(struct fpu *fpu)
{
fpu__clear(fpu, false);
}
/*
* Load FPU context before returning to userspace.
*/
void switch_fpu_return(void)
{
if (!static_cpu_has(X86_FEATURE_FPU))
return;
__fpregs_load_activate();
}
EXPORT_SYMBOL_GPL(switch_fpu_return);
#ifdef CONFIG_X86_DEBUG_FPU
/*
* If current FPU state according to its tracking (loaded FPU context on this
* CPU) is not valid then we must have TIF_NEED_FPU_LOAD set so the context is
* loaded on return to userland.
*/
void fpregs_assert_state_consistent(void)
{
struct fpu *fpu = &current->thread.fpu;
if (test_thread_flag(TIF_NEED_FPU_LOAD))
return;
WARN_ON_FPU(!fpregs_state_valid(fpu, smp_processor_id()));
}
EXPORT_SYMBOL_GPL(fpregs_assert_state_consistent);
#endif
void fpregs_mark_activate(void)
{
struct fpu *fpu = &current->thread.fpu;
fpregs_activate(fpu);
fpu->last_cpu = smp_processor_id();
clear_thread_flag(TIF_NEED_FPU_LOAD);
}
EXPORT_SYMBOL_GPL(fpregs_mark_activate);
/*
* x87 math exception handling:
*/
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.
*/
if (boot_cpu_has(X86_FEATURE_FXSR)) {
cwd = fpu->state.fxsave.cwd;
swd = fpu->state.fxsave.swd;
} else {
cwd = (unsigned short)fpu->state.fsave.cwd;
swd = (unsigned short)fpu->state.fsave.swd;
}
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 = MXCSR_DEFAULT;
if (boot_cpu_has(X86_FEATURE_XMM))
mxcsr = fpu->state.fxsave.mxcsr;
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;
}