From bf3577c044e51094ca2166e748c8bae360c3f0c2 Mon Sep 17 00:00:00 2001
From: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Date: Wed, 24 May 2023 07:26:04 -0400
Subject: [PATCH 14/15] target/i386: add support for FB_CLEAR feature

RH-Author: Emanuele Giuseppe Esposito <eesposit@redhat.com>
RH-MergeRequest: 281: target/i386: add support for FLUSH_L1D feature
RH-Bugzilla: 2216203
RH-Acked-by: Miroslav Rezanina <mrezanin@redhat.com>
RH-Acked-by: Jon Maloy <jmaloy@redhat.com>
RH-Commit: [2/2] 8cd4b7366a9898e406ca20c9a28f14ddce855b1e

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2216203

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 47da059df6..9d3dcdcc0d 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -981,7 +981,7 @@ 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 7cb7cea8ab..9b7d664ee7 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -950,6 +950,7 @@ 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)
 
-- 
2.37.3