[PATCH v5 7/8] KVM: nSVM: Advertise DecodeAssists to L1

Advertise DecodeAssists to L1 now that KVM virtualizes the
guest-visible DecodeAssist state in VMCB12: EXITINFO1 decode data for
MOV CR/DR, INTn, and INVLPG exits, plus instruction bytes for nested
page faults and intercepted #PF exits.  INVLPGA's linear address remains
available directly from the saved guest rAX, as required by the APM.

Expose the feature only when supported by hardware, as KVM still relies
on hardware DecodeAssists for VM-Exits that are reflected directly from
L2.

With DecodeAssists exposed, QEMU configurations that require the feature
(e.g. "-cpu ...,+decodeassists,...,enforce") are no longer rejected.

Signed-off-by: Tina Zhang <[email protected]>
---
 arch/x86/kvm/cpuid.c   | 1 +
 arch/x86/kvm/svm/svm.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ddb022cb203a..b644e45eac71 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1208,6 +1208,7 @@ void kvm_initialize_cpu_caps(void)
 		VENDOR_F(NPT),
 		VENDOR_F(VMCBCLEAN),
 		VENDOR_F(FLUSHBYASID),
+		VENDOR_F(DECODEASSISTS),
 		VENDOR_F(NRIPS),
 		VENDOR_F(TSCRATEMSR),
 		VENDOR_F(V_VMSAVE_VMLOAD),
diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index 5426a9669053..a99a1dc3426f 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -5560,6 +5560,8 @@ static __init void svm_set_cpu_caps(void)
 		 */
 		kvm_cpu_cap_set(X86_FEATURE_FLUSHBYASID);
 
+		kvm_cpu_cap_check_and_set(X86_FEATURE_DECODEASSISTS);
+
 		if (nrips)
 			kvm_cpu_cap_set(X86_FEATURE_NRIPS);
 
-- 
2.43.7