diff options
| author | Pawan Gupta <pawan.kumar.gupta@linux.intel.com> | 2019-10-23 12:23:33 +0200 |
|---|---|---|
| committer | Ben Hutchings <ben@decadent.org.uk> | 2019-11-15 00:56:50 +0000 |
| commit | 67323ec3ec3be6f5fcf2d6373701716b50c2a59d (patch) | |
| tree | aa58e18db4dc455531c1fc47bc2797d3a808d48e /arch | |
| parent | f21f3516be7ce2340f1afd5c3513c6319ca23d2f (diff) | |
kvm/x86: Export MDS_NO=0 to guests when TSX is enabled
commit e1d38b63acd843cfdd4222bf19a26700fd5c699e upstream.
Export the IA32_ARCH_CAPABILITIES MSR bit MDS_NO=0 to guests on TSX
Async Abort(TAA) affected hosts that have TSX enabled and updated
microcode. This is required so that the guests don't complain,
"Vulnerable: Clear CPU buffers attempted, no microcode"
when the host has the updated microcode to clear CPU buffers.
Microcode update also adds support for MSR_IA32_TSX_CTRL which is
enumerated by the ARCH_CAP_TSX_CTRL bit in IA32_ARCH_CAPABILITIES MSR.
Guests can't do this check themselves when the ARCH_CAP_TSX_CTRL bit is
not exported to the guests.
In this case export MDS_NO=0 to the guests. When guests have
CPUID.MD_CLEAR=1, they deploy MDS mitigation which also mitigates TAA.
Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Neelima Krishnan <neelima.krishnan@intel.com>
Reviewed-by: Tony Luck <tony.luck@intel.com>
Reviewed-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Diffstat (limited to 'arch')
| -rw-r--r-- | arch/x86/kvm/x86.c | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 6275494c7ee0..f9e374b696b9 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -924,6 +924,25 @@ u64 kvm_get_arch_capabilities(void) if (!boot_cpu_has_bug(X86_BUG_MDS)) data |= ARCH_CAP_MDS_NO; + /* + * On TAA affected systems, export MDS_NO=0 when: + * - TSX is enabled on the host, i.e. X86_FEATURE_RTM=1. + * - Updated microcode is present. This is detected by + * the presence of ARCH_CAP_TSX_CTRL_MSR and ensures + * that VERW clears CPU buffers. + * + * When MDS_NO=0 is exported, guests deploy clear CPU buffer + * mitigation and don't complain: + * + * "Vulnerable: Clear CPU buffers attempted, no microcode" + * + * If TSX is disabled on the system, guests are also mitigated against + * TAA and clear CPU buffer mitigation is not required for guests. + */ + if (boot_cpu_has_bug(X86_BUG_TAA) && boot_cpu_has(X86_FEATURE_RTM) && + (data & ARCH_CAP_TSX_CTRL_MSR)) + data &= ~ARCH_CAP_MDS_NO; + return data; } |