linux-kernel - [PATCH 48/61] KVM: x86: Do host CPUID at load time to mask KVM cpu caps

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Message-Id: <20200201185218.24473-49-sean.j.christopherson@intel.com>
Date:   Sat,  1 Feb 2020 10:52:05 -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
Subject: [PATCH 48/61] KVM: x86: Do host CPUID at load time to mask KVM cpu caps

Mask kvm_cpu_caps based on host CPUID in preparation for overriding the
CPUID results during KVM_GET_SUPPORTED_CPUID instead of doing the
masking at runtime.

Note, masking may or may not be necessary, e.g. the kernel rarely, if
ever, sets real CPUID bits that are not supported by hardware.  But, the
code is cheap and only runs once at load, so an abundance of caution is
warranted.

No functional change intended.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/cpuid.c | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index ab2a34337588..4416f2422321 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -272,8 +272,22 @@ static __always_inline void cpuid_entry_mask(struct kvm_cpuid_entry2 *entry,
 
 static __always_inline void kvm_cpu_cap_mask(enum cpuid_leafs leaf, u32 mask)
 {
+	const struct cpuid_reg cpuid = x86_feature_cpuid(leaf * 32);
+	struct kvm_cpuid_entry2 entry;
+
 	reverse_cpuid_check(leaf);
 	kvm_cpu_caps[leaf] &= mask;
+
+#ifdef CONFIG_KVM_CPUID_AUDIT
+	/* Entry needs to be fully populated when auditing is enabled. */
+	entry.function = cpuid.function;
+	entry.index = cpuid.index;
+#endif
+
+	cpuid_count(cpuid.function, cpuid.index,
+		    &entry.eax, &entry.ebx, &entry.ecx, &entry.edx);
+
+	kvm_cpu_caps[leaf] &= *__cpuid_entry_get_reg(&entry, &cpuid);
 }
 
 void kvm_set_cpu_caps(void)
-- 
2.24.1