[PATCH 3.16 112/148] KVM: x86: fix presentation of TSX feature in ARCH_CAPABILITIES

[Ben Hutchings]

3.16.82-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[bwh: Backported to 3.16: adjust context]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- 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;
 }