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qemu-kvm/SOURCES/kvm-target-i386-add-support...

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From 0d056d6da9e4147d5965bf3507f6d6d6a413924d Mon Sep 17 00:00:00 2001
From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Date: Wed, 24 May 2023 06:52:43 -0400
Subject: [PATCH 2/5] target/i386: add support for FB_CLEAR feature
RH-Author: Emanuele Giuseppe Esposito <eesposit@redhat.com>
RH-MergeRequest: 167: target/i386: add support for FB_CLEAR feature
RH-Bugzilla: 2216201
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Commit: [2/2] 5f191964ba25754107a06ef907f4ac614280aaa1 (eesposit/qemu-kvm)
Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2216201
commit 22e1094ca82d5518c1b69aff3e87c550776ae1eb
Author: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Date: Wed Feb 1 08:57:59 2023 -0500
target/i386: add support for FB_CLEAR feature
As reported by the Intel's doc:
"FB_CLEAR: The processor will overwrite fill buffer values as part of
MD_CLEAR operations with the VERW instruction.
On these processors, L1D_FLUSH does not overwrite fill buffer values."
If this cpu feature is present in host, allow QEMU to choose whether to
show it to the guest too.
One disadvantage of not exposing it is that the guest will report
a non existing vulnerability in
/sys/devices/system/cpu/vulnerabilities/mmio_stale_data
because the mitigation is present only when the cpu has
(FLUSH_L1D and MD_CLEAR) or FB_CLEAR
features enabled.
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Message-Id: <20230201135759.555607-3-eesposit@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
---
target/i386/cpu.c | 2 +-
target/i386/cpu.h | 1 +
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index caf6338cc0..839706b430 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -1012,7 +1012,7 @@ FeatureWordInfo feature_word_info[FEATURE_WORDS] = {
"ssb-no", "mds-no", "pschange-mc-no", "tsx-ctrl",
"taa-no", NULL, NULL, NULL,
NULL, NULL, NULL, NULL,
- NULL, NULL, NULL, NULL,
+ NULL, "fb-clear", NULL, NULL,
NULL, NULL, NULL, NULL,
NULL, NULL, NULL, NULL,
NULL, NULL, NULL, NULL,
diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 74fa649b60..c28b9df217 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -989,6 +989,7 @@ uint64_t x86_cpu_get_supported_feature_word(FeatureWord w,
#define MSR_ARCH_CAP_PSCHANGE_MC_NO (1U << 6)
#define MSR_ARCH_CAP_TSX_CTRL_MSR (1U << 7)
#define MSR_ARCH_CAP_TAA_NO (1U << 8)
+#define MSR_ARCH_CAP_FB_CLEAR (1U << 17)
#define MSR_CORE_CAP_SPLIT_LOCK_DETECT (1U << 5)
--
2.39.3