88 lines
3.0 KiB
Diff
88 lines
3.0 KiB
Diff
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From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
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From: Rich Ercolani <214141+rincebrain@users.noreply.github.com>
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Date: Sat, 26 Aug 2023 14:25:46 -0400
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Subject: [PATCH] Avoid save/restoring AMX registers to avoid a SPR erratum
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Intel SPR erratum SPR4 says that if you trip into a vmexit while
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doing FPU save/restore, your AMX register state might misbehave...
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and by misbehave, I mean save all zeroes incorrectly, leading to
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explosions if you restore it.
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Since we're not using AMX for anything, the simple way to avoid
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this is to just not save/restore those when we do anything, since
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we're killing preemption of any sort across our save/restores.
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If we ever decide to use AMX, it's not clear that we have any
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way to mitigate this, on Linux...but I am not an expert.
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Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
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Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
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Closes #14989
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Closes #15168
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(cherry picked from commit 277f2e587b085d1eb8aa48b4ac0768a9ef5745ab)
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Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
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---
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include/os/linux/kernel/linux/simd_x86.h | 19 ++++++++++++++-----
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1 file changed, 14 insertions(+), 5 deletions(-)
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diff --git a/include/os/linux/kernel/linux/simd_x86.h b/include/os/linux/kernel/linux/simd_x86.h
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index 660f0d42d..455167ac8 100644
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--- a/include/os/linux/kernel/linux/simd_x86.h
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+++ b/include/os/linux/kernel/linux/simd_x86.h
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@@ -157,6 +157,15 @@
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#endif
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#endif
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+#ifndef XFEATURE_MASK_XTILE
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+/*
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+ * For kernels where this doesn't exist yet, we still don't want to break
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+ * by save/restoring this broken nonsense.
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+ * See issue #14989 or Intel errata SPR4 for why
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+ */
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+#define XFEATURE_MASK_XTILE 0x60000
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+#endif
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+
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#include <linux/mm.h>
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#include <linux/slab.h>
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@@ -319,18 +328,18 @@ kfpu_begin(void)
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union fpregs_state *state = zfs_kfpu_fpregs[smp_processor_id()];
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#if defined(HAVE_XSAVES)
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if (static_cpu_has(X86_FEATURE_XSAVES)) {
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- kfpu_do_xsave("xsaves", &state->xsave, ~0);
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+ kfpu_do_xsave("xsaves", &state->xsave, ~XFEATURE_MASK_XTILE);
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return;
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}
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#endif
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#if defined(HAVE_XSAVEOPT)
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if (static_cpu_has(X86_FEATURE_XSAVEOPT)) {
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- kfpu_do_xsave("xsaveopt", &state->xsave, ~0);
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+ kfpu_do_xsave("xsaveopt", &state->xsave, ~XFEATURE_MASK_XTILE);
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return;
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}
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#endif
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if (static_cpu_has(X86_FEATURE_XSAVE)) {
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- kfpu_do_xsave("xsave", &state->xsave, ~0);
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+ kfpu_do_xsave("xsave", &state->xsave, ~XFEATURE_MASK_XTILE);
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} else if (static_cpu_has(X86_FEATURE_FXSR)) {
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kfpu_save_fxsr(&state->fxsave);
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} else {
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@@ -415,12 +424,12 @@ kfpu_end(void)
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union fpregs_state *state = zfs_kfpu_fpregs[smp_processor_id()];
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#if defined(HAVE_XSAVES)
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if (static_cpu_has(X86_FEATURE_XSAVES)) {
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- kfpu_do_xrstor("xrstors", &state->xsave, ~0);
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+ kfpu_do_xrstor("xrstors", &state->xsave, ~XFEATURE_MASK_XTILE);
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goto out;
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}
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#endif
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if (static_cpu_has(X86_FEATURE_XSAVE)) {
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- kfpu_do_xrstor("xrstor", &state->xsave, ~0);
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+ kfpu_do_xrstor("xrstor", &state->xsave, ~XFEATURE_MASK_XTILE);
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} else if (static_cpu_has(X86_FEATURE_FXSR)) {
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kfpu_restore_fxsr(&state->fxsave);
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} else {
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--
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2.39.2
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