linux-kernel - [PATCH 3/3] KVM: x86: Detect KVM_CPUID_FEATURES base before KVM PV feature CPUID updating

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Message-Id: <712ea6c3db34d5b488888648c1eb2db655eaa5b9.1680179693.git.houwenlong.hwl@antgroup.com>
Date:   Thu, 30 Mar 2023 20:35:54 +0800
From:   "Hou Wenlong" <houwenlong.hwl@...group.com>
To:     kvm@...r.kernel.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH 3/3] KVM: x86: Detect KVM_CPUID_FEATURES base before KVM PV feature CPUID updating

KVM_CPUID_FEATURES is detected after CPUID updating in kvm_set_cpuid(),
then 'vcpu->arch.kvm_cpuid_base' is NULL and KVM PV feature CPUID
updating wouldn't work. So detect it early before CPUID updating in
kvm_set_cpuid().

Fixes: ee3a5f9e3d9b ("KVM: x86: Do runtime CPUID update before updating vcpu->arch.cpuid_entries")
Signed-off-by: Hou Wenlong <houwenlong.hwl@...group.com>
---
 arch/x86/kvm/cpuid.c | 21 ++++++++++++++++-----
 1 file changed, 16 insertions(+), 5 deletions(-)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index af92d3422c79..0c8658fdb6c1 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -176,15 +176,15 @@ static int kvm_cpuid_check_equal(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2
 	return 0;
 }
 
-static struct kvm_hypervisor_cpuid kvm_get_hypervisor_cpuid(struct kvm_vcpu *vcpu,
-							    const char *sig)
+static struct kvm_hypervisor_cpuid __kvm_get_hypervisor_cpuid(struct kvm_cpuid_entry2 *entries,
+							      int nent, const char *sig)
 {
 	struct kvm_hypervisor_cpuid cpuid = {};
 	struct kvm_cpuid_entry2 *entry;
 	u32 base;
 
 	for_each_possible_hypervisor_cpuid_base(base) {
-		entry = kvm_find_cpuid_entry(vcpu, base);
+		entry = cpuid_entry2_find(entries, nent, base, KVM_CPUID_INDEX_NOT_SIGNIFICANT);
 
 		if (entry) {
 			u32 signature[3];
@@ -202,6 +202,14 @@ static struct kvm_hypervisor_cpuid kvm_get_hypervisor_cpuid(struct kvm_vcpu *vcp
 	}
 
 	return cpuid;
+
+}
+
+static struct kvm_hypervisor_cpuid kvm_get_hypervisor_cpuid(struct kvm_vcpu *vcpu,
+							    const char *sig)
+{
+	return __kvm_get_hypervisor_cpuid(vcpu->arch.cpuid_entries,
+					  vcpu->arch.cpuid_nent, sig);
 }
 
 static struct kvm_cpuid_entry2 *__kvm_find_kvm_cpuid_features(struct kvm_vcpu *vcpu,
@@ -406,9 +414,12 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
                         int nent)
 {
 	int r;
+	struct kvm_hypervisor_cpuid kvm_cpuid;
 
 	__kvm_update_cpuid_runtime(vcpu, e2, nent);
-	kvm_update_pv_cpuid(vcpu, e2, nent);
+	kvm_cpuid = __kvm_get_hypervisor_cpuid(e2, nent, KVM_SIGNATURE);
+	if (kvm_cpuid.base)
+		kvm_update_pv_cpuid(vcpu, e2, nent);
 
 	/*
 	 * KVM does not correctly handle changing guest CPUID after KVM_RUN, as
@@ -444,7 +455,7 @@ static int kvm_set_cpuid(struct kvm_vcpu *vcpu, struct kvm_cpuid_entry2 *e2,
 	vcpu->arch.cpuid_entries = e2;
 	vcpu->arch.cpuid_nent = nent;
 
-	vcpu->arch.kvm_cpuid = kvm_get_hypervisor_cpuid(vcpu, KVM_SIGNATURE);
+	vcpu->arch.kvm_cpuid = kvm_cpuid;
 	vcpu->arch.xen.cpuid = kvm_get_hypervisor_cpuid(vcpu, XEN_SIGNATURE);
 	kvm_vcpu_after_set_cpuid(vcpu);
 
-- 
2.31.1