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Avoid save/restoring AMX registers to avoid a SPR erratum #15168

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Aug 26, 2023
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Avoid save/restoring AMX registers to avoid a SPR erratum #15168

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19 changes: 14 additions & 5 deletions include/os/linux/kernel/linux/simd_x86.h
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Original file line number Diff line number Diff line change
Expand Up @@ -147,6 +147,15 @@
#error "Toolchain needs to support the XSAVE assembler instruction"
#endif

#ifndef XFEATURE_MASK_XTILE
/*
* For kernels where this doesn't exist yet, we still don't want to break
* by save/restoring this broken nonsense.
* See issue #14989 or Intel errata SPR4 for why
*/
#define XFEATURE_MASK_XTILE 0x60000
#endif

#include <linux/mm.h>
#include <linux/slab.h>

Expand Down Expand Up @@ -315,18 +324,18 @@ kfpu_begin(void)
uint8_t *state = zfs_kfpu_fpregs[smp_processor_id()];
#if defined(HAVE_XSAVES)
if (static_cpu_has(X86_FEATURE_XSAVES)) {
kfpu_do_xsave("xsaves", state, ~0);
kfpu_do_xsave("xsaves", state, ~XFEATURE_MASK_XTILE);
return;
}
#endif
#if defined(HAVE_XSAVEOPT)
if (static_cpu_has(X86_FEATURE_XSAVEOPT)) {
kfpu_do_xsave("xsaveopt", state, ~0);
kfpu_do_xsave("xsaveopt", state, ~XFEATURE_MASK_XTILE);
return;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
kfpu_do_xsave("xsave", state, ~0);
kfpu_do_xsave("xsave", state, ~XFEATURE_MASK_XTILE);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_save_fxsr(state);
} else {
Expand Down Expand Up @@ -376,12 +385,12 @@ kfpu_end(void)
uint8_t *state = zfs_kfpu_fpregs[smp_processor_id()];
#if defined(HAVE_XSAVES)
if (static_cpu_has(X86_FEATURE_XSAVES)) {
kfpu_do_xrstor("xrstors", state, ~0);
kfpu_do_xrstor("xrstors", state, ~XFEATURE_MASK_XTILE);
goto out;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
kfpu_do_xrstor("xrstor", state, ~0);
kfpu_do_xrstor("xrstor", state, ~XFEATURE_MASK_XTILE);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_restore_fxsr(state);
} else {
Expand Down