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@linux.intel.com Signed-off-by: Dave Hansen dave.hansen@linux.intel.com Reviewed-by: Dave Hansen dave.hansen@linux.intel.com --- 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 513f00f02856..087d6ceaaf0c 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(); }