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backport fix for AMX register breakage

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vmexit's can cause the AMX registers to "misbehave" which can break
ZFS, even though ZFS doesn't use AMX at all.

This causes crashes and processes hanging forever in uninterruptible
sleep (the infamous D state) on Intel Xeon 4th gen HW, possible other
HW too, but we only got reports on Sapphire Rapids models.

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
Tested-by: Aaron Lauterer <a.lauterer@proxmox.com>
This commit is contained in:
Thomas Lamprecht 2023-10-10 14:55:48 +02:00
parent 8c6520d1fc
commit 9e8946d4b9
2 changed files with 88 additions and 0 deletions
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87
debian/patches/0011-Avoid-save-restoring-AMX-registers-to-avoid-a-SPR-er.patch vendored Normal file
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@ -0,0 +1,87 @@
From 0000000000000000000000000000000000000000 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 <behlendorf1@llnl.gov>
Signed-off-by: Rich Ercolani <rincebrain@gmail.com>
Closes #14989
Closes #15168
(cherry picked from commit 277f2e587b085d1eb8aa48b4ac0768a9ef5745ab)
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
---
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 660f0d42d..455167ac8 100644
--- a/include/os/linux/kernel/linux/simd_x86.h
+++ b/include/os/linux/kernel/linux/simd_x86.h
@@ -157,6 +157,15 @@
#endif
#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>
@@ -319,18 +328,18 @@ kfpu_begin(void)
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);
+ kfpu_do_xsave("xsaves", &state->xsave, ~XFEATURE_MASK_XTILE);
return;
}
#endif
#if defined(HAVE_XSAVEOPT)
if (static_cpu_has(X86_FEATURE_XSAVEOPT)) {
- kfpu_do_xsave("xsaveopt", &state->xsave, ~0);
+ kfpu_do_xsave("xsaveopt", &state->xsave, ~XFEATURE_MASK_XTILE);
return;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
- kfpu_do_xsave("xsave", &state->xsave, ~0);
+ kfpu_do_xsave("xsave", &state->xsave, ~XFEATURE_MASK_XTILE);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_save_fxsr(&state->fxsave);
} else {
@@ -415,12 +424,12 @@ 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);
+ kfpu_do_xrstor("xrstors", &state->xsave, ~XFEATURE_MASK_XTILE);
goto out;
}
#endif
if (static_cpu_has(X86_FEATURE_XSAVE)) {
- kfpu_do_xrstor("xrstor", &state->xsave, ~0);
+ kfpu_do_xrstor("xrstor", &state->xsave, ~XFEATURE_MASK_XTILE);
} else if (static_cpu_has(X86_FEATURE_FXSR)) {
kfpu_restore_fxsr(&state->fxsave);
} else {
--
2.39.2

1
debian/patches/series vendored
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@ -8,3 +8,4 @@
0008-Patch-move-manpage-arcstat-1-to-arcstat-8.patch
0009-arcstat-Fix-integer-division-with-python3.patch
0010-arc-stat-summary-guard-access-to-l2arc-MFU-MRU-stats.patch
0011-Avoid-save-restoring-AMX-registers-to-avoid-a-SPR-er.patch