Commit e95df4ec authored by Pawan Gupta's avatar Pawan Gupta Committed by Dave Hansen
Browse files

x86/mmio: Disable KVM mitigation when X86_FEATURE_CLEAR_CPU_BUF is set 



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: default avatarPawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
Reviewed-by: default avatarDave Hansen <dave.hansen@linux.intel.com>
parent 90d35da6

arch/x86/kernel/cpu/bugs.c

+12 −2
Original line number Diff line number Diff line
@@ -422,6 +422,13 @@ 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);
@@ -498,8 +505,11 @@ 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();

	}