[PATCH v3 2/5] KVM: nSVM: Disable LBRV in nested control cache when unsupported

[Shivansh Dhiman <shivansh.dhiman@amd.com>]

Clear SVM_MISC2_ENABLE_V_LBR in __nested_copy_vmcb_control_to_cache() when
the vCPU does not support LBR Virtualization. This lets the cached value be
consumed directly instead of re-checking X86_FEATURE_LBRV on every access.

Suggested-by: Yosry Ahmed <yosry@kernel.org>
Signed-off-by: Shivansh Dhiman <shivansh.dhiman@amd.com>
---
Changelog:
v3:
 * New patch.
 * Sanitize V_LBR in the cache and drop the redundant X86_FEATURE_LBRV 
   checks (Yosry Ahmed).

---
 arch/x86/kvm/svm/nested.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index d3df6b22bfef..84248e6665cf 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -534,6 +534,11 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	if (!gmet_enabled || !guest_cpu_cap_has(vcpu, X86_FEATURE_GMET))
 		to->misc_ctl &= ~SVM_MISC_ENABLE_GMET;
 
+	/* Always clear misc_ctl2 bits that the guest cannot use */
+	to->misc_ctl2 = from->misc_ctl2;
+	if (!lbrv || !guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV))
+		to->misc_ctl2 &= ~SVM_MISC2_ENABLE_V_LBR;
+
 	to->iopm_base_pa        = from->iopm_base_pa & PAGE_MASK;
 	to->msrpm_base_pa       = from->msrpm_base_pa & PAGE_MASK;
 	to->tsc_offset          = from->tsc_offset;
@@ -551,7 +556,6 @@ void __nested_copy_vmcb_control_to_cache(struct kvm_vcpu *vcpu,
 	to->event_inj_err       = from->event_inj_err;
 	to->next_rip            = from->next_rip;
 	to->nested_cr3          = from->nested_cr3;
-	to->misc_ctl2		= from->misc_ctl2;
 	to->pause_filter_count  = from->pause_filter_count;
 	to->pause_filter_thresh = from->pause_filter_thresh;
 
@@ -738,8 +742,7 @@ static int nested_svm_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,
 
 bool nested_vmcb12_has_lbrv(struct kvm_vcpu *vcpu)
 {
-	return guest_cpu_cap_has(vcpu, X86_FEATURE_LBRV) &&
-		(to_svm(vcpu)->nested.ctl.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR);
+	return to_svm(vcpu)->nested.ctl.misc_ctl2 & SVM_MISC2_ENABLE_V_LBR;
 }
 
 static void nested_vmcb02_prepare_save(struct vcpu_svm *svm)
-- 
2.43.0