KVM: x86: fix presentation of TSX feature in ARCH_CAPABILITIES

commit cbbaa2727aa3ae9e0a844803da7cef7fd3b94f2b upstream.

KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented
to the guests.  It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR &&
!RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not
hidden (it actually was), yet the value says that TSX is not vulnerable
to microarchitectural data sampling.  Fix both.

Tested-by: Jim Mattson <jmattson@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d6711e5b9e781446469e19d1d0837b81d22e338d..bb4ed9190cbcc322b48fc9d1c5e47f51e2b40f47 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -945,10 +945,15 @@ u64 kvm_get_arch_capabilities(void)
         * 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))
+       if (!boot_cpu_has(X86_FEATURE_RTM))
+               data &= ~ARCH_CAP_TAA_NO;
+       else if (!boot_cpu_has_bug(X86_BUG_TAA))
+               data |= ARCH_CAP_TAA_NO;
+       else if (data & ARCH_CAP_TSX_CTRL_MSR)
                data &= ~ARCH_CAP_MDS_NO;
 
+       /* KVM does not emulate MSR_IA32_TSX_CTRL.  */
+       data &= ~ARCH_CAP_TSX_CTRL_MSR;
        return data;
 }