linux-kernel - [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

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Date:   Mon,  2 Mar 2020 15:57:07 -0800
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Xiaoyao Li <xiaoyao.li@...el.com>
Subject: [PATCH v2 64/66] KVM: nSVM: Expose SVM features to L1 iff nested is enabled

Set SVM feature bits in KVM capabilities if and only if nested=true, KVM
shouldn't advertise features that realistically can't be used.  Use
kvm_cpu_cap_has(X86_FEATURE_SVM) to indirectly query "nested" in
svm_set_supported_cpuid() in anticipation of moving CPUID 0x8000000A
adjustments into common x86 code.

Suggested-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/svm.c | 22 +++++++++++++---------
 1 file changed, 13 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index f32fc3c03667..8e39dcd3160d 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -1373,21 +1373,21 @@ static __init void svm_set_cpu_caps(void)
 	if (avic)
 		kvm_cpu_cap_clear(X86_FEATURE_X2APIC);
 
-	/* CPUID 0x80000001 */
-	if (nested)
+	/* CPUID 0x80000001 and 0x8000000A (SVM features) */
+	if (nested) {
 		kvm_cpu_cap_set(X86_FEATURE_SVM);
 
+		if (boot_cpu_has(X86_FEATURE_NRIPS))
+			kvm_cpu_cap_set(X86_FEATURE_NRIPS);
+
+		if (npt_enabled)
+			kvm_cpu_cap_set(X86_FEATURE_NPT);
+	}
+
 	/* CPUID 0x80000008 */
 	if (boot_cpu_has(X86_FEATURE_LS_CFG_SSBD) ||
 	    boot_cpu_has(X86_FEATURE_AMD_SSBD))
 		kvm_cpu_cap_set(X86_FEATURE_VIRT_SSBD);
-
-	/* CPUID 0x8000000A */
-	/* Support next_rip if host supports it */
-	kvm_cpu_cap_check_and_set(X86_FEATURE_NRIPS);
-
-	if (npt_enabled)
-		kvm_cpu_cap_set(X86_FEATURE_NPT);
 }
 
 static __init int svm_hardware_setup(void)
@@ -6051,6 +6051,10 @@ static void svm_set_supported_cpuid(struct kvm_cpuid_entry2 *entry)
 {
 	switch (entry->function) {
 	case 0x8000000A:
+		if (!kvm_cpu_cap_has(X86_FEATURE_SVM)) {
+			entry->eax = entry->ebx = entry->ecx = entry->edx = 0;
+			break;
+		}
 		entry->eax = 1; /* SVM revision 1 */
 		entry->ebx = 8; /* Lets support 8 ASIDs in case we add proper
 				   ASID emulation to nested SVM */
-- 
2.24.1