This is a note to let you know that I've just added the patch titled
x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
x86-mmio-disable-kvm-mitigation-when-x86_feature_clear_cpu_buf-is-set.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 90c3bf0d91fa5b7f671b830350d5c052dc26295a Mon Sep 17 00:00:00 2001
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Date: Mon, 11 Mar 2024 12:29:43 -0700
Subject: x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set
From: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
commit e95df4ec0c0c9791941f112db699fae794b9862a upstream.
Currently MMIO Stale Data mitigation for CPUs not affected by MDS/TAA is
to only deploy VERW at VMentry by enabling mmio_stale_data_clear static
branch. No mitigation is needed for kernel->user transitions. If such
CPUs are also affected by RFDS, its mitigation may set
X86_FEATURE_CLEAR_CPU_BUF to deploy VERW at kernel->user and VMentry.
This could result in duplicate VERW at VMentry.
Fix this by disabling mmio_stale_data_clear static branch when
X86_FEATURE_CLEAR_CPU_BUF is enabled.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@xxxxxxxxxxxxxxx>
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Reviewed-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/x86/kernel/cpu/bugs.c | 14 ++++++++++++--
1 file changed, 12 insertions(+), 2 deletions(-)
--- a/arch/x86/kernel/cpu/bugs.c
+++ b/arch/x86/kernel/cpu/bugs.c
@@ -421,6 +421,13 @@ static void __init mmio_select_mitigatio
if (boot_cpu_has_bug(X86_BUG_MDS) || (boot_cpu_has_bug(X86_BUG_TAA) &&
boot_cpu_has(X86_FEATURE_RTM)))
setup_force_cpu_cap(X86_FEATURE_CLEAR_CPU_BUF);
+
+ /*
+ * X86_FEATURE_CLEAR_CPU_BUF could be enabled by other VERW based
+ * mitigations, disable KVM-only mitigation in that case.
+ */
+ if (boot_cpu_has(X86_FEATURE_CLEAR_CPU_BUF))
+ static_branch_disable(&mmio_stale_data_clear);
else
static_branch_enable(&mmio_stale_data_clear);
@@ -497,8 +504,11 @@ static void __init md_clear_update_mitig
taa_mitigation = TAA_MITIGATION_VERW;
taa_select_mitigation();
}
- if (mmio_mitigation == MMIO_MITIGATION_OFF &&
- boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
+ /*
+ * MMIO_MITIGATION_OFF is not checked here so that mmio_stale_data_clear
+ * gets updated correctly as per X86_FEATURE_CLEAR_CPU_BUF state.
+ */
+ if (boot_cpu_has_bug(X86_BUG_MMIO_STALE_DATA)) {
mmio_mitigation = MMIO_MITIGATION_VERW;
mmio_select_mitigation();
}
Patches currently in stable-queue which might be from pawan.kumar.gupta@xxxxxxxxxxxxxxx are
queue-6.1/documentation-hw-vuln-add-documentation-for-rfds.patch
queue-6.1/x86-rfds-mitigate-register-file-data-sampling-rfds.patch
queue-6.1/x86-mmio-disable-kvm-mitigation-when-x86_feature_clear_cpu_buf-is-set.patch
queue-6.1/kvm-x86-export-rfds_no-and-rfds_clear-to-guests.patch
