linux-kernel - Re: [PATCH 0/6] KVM: x86: CPUID emulation and tracing fixes

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Date:   Tue, 3 Mar 2020 09:48:44 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     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, Jan Kiszka <jan.kiszka@...mens.com>,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH 0/6] KVM: x86: CPUID emulation and tracing fixes

On 02/03/20 20:57, Sean Christopherson wrote:
> Two fixes related to out-of-range CPUID emulation and related cleanup on
> top.
> 
> I have a unit test and also manually verified a few interesting cases.
> I'm not planning on posting the unit test at this time because I haven't
> figured out how to avoid false positives, e.g. if a random in-bounds
> leaf just happens to match the output of a max basic leaf.  It might be
> doable by hardcoding the cpu model?

It would be best suited for selftests rather than kvm-unit-tests.  But I 
don't really see the benefit of anything more than just

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index b1c469446b07..c1abf5de4461 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -1001,6 +1001,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 	       u32 *ecx, u32 *edx, bool check_limit)
 {
 	u32 function = *eax, index = *ecx;
+	u32 orig_function = function;
 	struct kvm_cpuid_entry2 *entry;
 	struct kvm_cpuid_entry2 *max;
 	bool found;
@@ -1049,7 +1050,7 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
 			}
 		}
 	}
-	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, found);
+	trace_kvm_cpuid(orig_function, *eax, *ebx, *ecx, *edx, found);
 	return found;
 }
 EXPORT_SYMBOL_GPL(kvm_cpuid);