From a2b586df5546311f9be5f6acb9fe489b623c526e Mon Sep 17 00:00:00 2001 From: Pawan Gupta Date: Tue, 12 Mar 2024 14:11:19 -0700 Subject: [PATCH] x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set 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 Signed-off-by: Dave Hansen Reviewed-by: Dave Hansen Signed-off-by: Greg Kroah-Hartman --- arch/x86/kernel/cpu/bugs.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/bugs.c b/arch/x86/kernel/cpu/bugs.c index d8d1c86d55b9..c1b6c932cb5a 100644 --- a/arch/x86/kernel/cpu/bugs.c +++ b/arch/x86/kernel/cpu/bugs.c @@ -428,6 +428,13 @@ static void __init mmio_select_mitigation(void) 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); @@ -504,8 +511,11 @@ static void __init md_clear_update_mitigation(void) 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(); }