From c65aaa83876f9764f9017db278cefa453e1a3f5b Mon Sep 17 00:00:00 2001 From: Rich Ercolani <214141+rincebrain@users.noreply.github.com> Date: Sat, 26 Aug 2023 14:25:46 -0400 Subject: [PATCH] Avoid save/restoring AMX registers to avoid a SPR erratum Intel SPR erratum SPR4 says that if you trip into a vmexit while doing FPU save/restore, your AMX register state might misbehave... and by misbehave, I mean save all zeroes incorrectly, leading to explosions if you restore it. Since we're not using AMX for anything, the simple way to avoid this is to just not save/restore those when we do anything, since we're killing preemption of any sort across our save/restores. If we ever decide to use AMX, it's not clear that we have any way to mitigate this, on Linux...but I am not an expert. Reviewed-by: Brian Behlendorf Signed-off-by: Rich Ercolani Closes #14989 Closes #15168 --- include/os/linux/kernel/linux/simd_x86.h | 19 ++++++++++++++----- 1 file changed, 14 insertions(+), 5 deletions(-) diff --git a/include/os/linux/kernel/linux/simd_x86.h b/include/os/linux/kernel/linux/simd_x86.h index 1d77f0487a30..699b8a571824 100644 --- a/include/os/linux/kernel/linux/simd_x86.h +++ b/include/os/linux/kernel/linux/simd_x86.h @@ -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 #include @@ -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 { @@ -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 {