linux-kernel - [PATCH v2 49/66] KVM: x86: Do host CPUID at load time to mask KVM cpu caps

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Message-Id: <20200302235709.27467-50-sean.j.christopherson@intel.com>
Date:   Mon,  2 Mar 2020 15:56:52 -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 49/66] 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.

Reviewed-by: Vitaly Kuznetsov <vkuznets@...hat.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/cpuid.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 49527dbcc90c..ec8e24b1c1a7 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -272,8 +272,16 @@ 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;
+
+	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