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Linux 5.16 compat: don't use XSTATE_XSAVE to save FPU state

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Linux 5.16 moved XSTATE_XSAVE and XSTATE_XRESTORE out of our reach,
so add our own XSAVE{,OPT,S} code and use it for Linux 5.16.

Please note that this differs from previous behavior in that it
won't handle exceptions created by XSAVE an XRSTOR. This is sensible
for three reasons.

 - Exceptions during XSAVE and XRSTOR can only occur if the feature
   is not supported or enabled or the memory operand isn't aligned
   on a 64 byte boundary. If this happens something else went
   terribly wrong, and it may be better to stop execution.

 - Previously we just printed a warning and didn't handle the fault,
   this is arguable for the above reason.

 - All other *SAVE instruction also don't handle exceptions, so this
   at least aligns behavior.

Finally add a test to catch such a regression in the future.

Reviewed-by: Tony Hutter <hutter2@llnl.gov>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Attila Fülöp <attila@fueloep.org>
Closes #13042
Closes #13059
This commit is contained in:
Attila Fülöp
2022-02-09 21:50:10 +01:00
committed by Tony Hutter
parent bb271d67e8
commit 3b52ccd7d7
9 changed files with 300 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files
include/os/linux/kernel/linux/simd_x86.h
+123 -2
View File
@@ -136,9 +136,27 @@
* When the kernel_fpu_* symbols are unavailable then provide our own
* versions which allow the FPU to be safely used.
*/
#if defined(HAVE_KERNEL_FPU_INTERNAL) || defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
#if defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
/*
* Some sanity checks.
* HAVE_KERNEL_FPU_INTERNAL and HAVE_KERNEL_FPU_XSAVE_INTERNAL are exclusive.
*/
#if defined(HAVE_KERNEL_FPU_INTERNAL)
#error "HAVE_KERNEL_FPU_INTERNAL and HAVE_KERNEL_FPU_XSAVE_INTERNAL defined"
#endif
/*
* For kernels >= 5.16 we have to use inline assembly with the XSAVE{,OPT,S}
* instructions, so we need the toolchain to support at least XSAVE.
*/
#if !defined(HAVE_XSAVE)
#error "Toolchain needs to support the XSAVE assembler instruction"
#endif
#endif
#include <linux/mm.h>
#include <linux/slab.h>
extern union fpregs_state **zfs_kfpu_fpregs;
@@ -191,7 +209,9 @@ kfpu_init(void)
}
#define kfpu_allowed() 1
#if defined(HAVE_KERNEL_FPU_INTERNAL)
#define ex_handler_fprestore ex_handler_default
#endif
/*
* FPU save and restore instructions.
@@ -206,6 +226,7 @@ kfpu_init(void)
#define kfpu_fxsr_clean(rval) __asm("fnclex; emms; fildl %P[addr]" \
: : [addr] "m" (rval));
#if defined(HAVE_KERNEL_FPU_INTERNAL)
static inline void
kfpu_save_xsave(struct xregs_state *addr, uint64_t mask)
{
@@ -217,6 +238,21 @@ kfpu_save_xsave(struct xregs_state *addr, uint64_t mask)
XSTATE_XSAVE(addr, low, hi, err);
WARN_ON_ONCE(err);
}
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL) */
#if defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
#define kfpu_do_xsave(instruction, addr, mask) \
{ \
uint32_t low, hi; \
\
low = mask; \
hi = (uint64_t)(mask) >> 32; \
__asm(instruction " %[dst]\n\t" \
: \
: [dst] "m" (*(addr)), "a" (low), "d" (hi) \
: "memory"); \
}
#endif /* defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL) */
static inline void
kfpu_save_fxsr(struct fxregs_state *addr)
@@ -233,6 +269,7 @@ kfpu_save_fsave(struct fregs_state *addr)
kfpu_fnsave(addr);
}
#if defined(HAVE_KERNEL_FPU_INTERNAL)
static inline void
kfpu_begin(void)
{
@@ -250,7 +287,6 @@ kfpu_begin(void)
* FPU state to be correctly preserved and restored.
*/
union fpregs_state *state = zfs_kfpu_fpregs[smp_processor_id()];
if (static_cpu_has(X86_FEATURE_XSAVE)) {
kfpu_save_xsave(&state->xsave, ~0);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
@@ -259,7 +295,50 @@ kfpu_begin(void)
kfpu_save_fsave(&state->fsave);
}
}
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL) */
#if defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
static inline void
kfpu_begin(void)
{
/*
* Preemption and interrupts must be disabled for the critical
* region where the FPU state is being modified.
*/
preempt_disable();
local_irq_disable();
/*
* The current FPU registers need to be preserved by kfpu_begin()
* and restored by kfpu_end(). They are stored in a dedicated
* per-cpu variable, not in the task struct, this allows any user
* FPU state to be correctly preserved and restored.
*/
union fpregs_state *state = zfs_kfpu_fpregs[smp_processor_id()];
#if defined(HAVE_XSAVES)
if (static_cpu_has(X86_FEATURE_XSAVES)) {
kfpu_do_xsave("xsaves", &state->xsave, ~0);
goto out;
}
#endif
#if defined(HAVE_XSAVEOPT)
if (static_cpu_has(X86_FEATURE_XSAVEOPT)) {
kfpu_do_xsave("xsaveopt", &state->xsave, ~0);
goto out;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
kfpu_do_xsave("xsave", &state->xsave, ~0);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_save_fxsr(&state->fxsave);
} else {
kfpu_save_fsave(&state->fsave);
}
out:
}
#endif /* defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL) */
#if defined(HAVE_KERNEL_FPU_INTERNAL)
static inline void
kfpu_restore_xsave(struct xregs_state *addr, uint64_t mask)
{
@@ -269,6 +348,21 @@ kfpu_restore_xsave(struct xregs_state *addr, uint64_t mask)
hi = mask >> 32;
XSTATE_XRESTORE(addr, low, hi);
}
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL) */
#if defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
#define kfpu_do_xrstor(instruction, addr, mask) \
{ \
uint32_t low, hi; \
\
low = mask; \
hi = (uint64_t)(mask) >> 32; \
__asm(instruction " %[src]" \
: \
: [src] "m" (*(addr)), "a" (low), "d" (hi) \
: "memory"); \
}
#endif /* defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL) */
static inline void
kfpu_restore_fxsr(struct fxregs_state *addr)
@@ -294,6 +388,7 @@ kfpu_restore_fsave(struct fregs_state *addr)
kfpu_frstor(addr);
}
#if defined(HAVE_KERNEL_FPU_INTERNAL)
static inline void
kfpu_end(void)
{
@@ -310,6 +405,32 @@ kfpu_end(void)
local_irq_enable();
preempt_enable();
}
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL) */
#if defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL)
static inline void
kfpu_end(void)
{
union fpregs_state *state = zfs_kfpu_fpregs[smp_processor_id()];
#if defined(HAVE_XSAVES)
if (static_cpu_has(X86_FEATURE_XSAVES)) {
kfpu_do_xrstor("xrstors", &state->xsave, ~0);
goto out;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
kfpu_do_xrstor("xrstor", &state->xsave, ~0);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_save_fxsr(&state->fxsave);
} else {
kfpu_save_fsave(&state->fsave);
}
out:
local_irq_enable();
preempt_enable();
}
#endif /* defined(HAVE_KERNEL_FPU_XSAVE_INTERNAL) */
#else
@@ -322,7 +443,7 @@ kfpu_end(void)
#define kfpu_init() 0
#define kfpu_fini() ((void) 0)
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL) */
#endif /* defined(HAVE_KERNEL_FPU_INTERNAL || HAVE_KERNEL_FPU_XSAVE_INTERNAL) */
#endif /* defined(KERNEL_EXPORTS_X86_FPU) */
/*