Re: [PATCH] kvm: x86: Make traced and returned value of kvm_cpuid consistent again

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 3/1/2020 6:47 PM, Jan Kiszka wrote:
> From: Jan Kiszka <jan.kiszka@siemens.com>
> 
> After 43561123ab37, found is not set correctly in case of leaves 0BH,
> 1FH, or anything out-of-range. This is currently harmless for the return
> value because the only caller evaluating it passes leaf 0x80000008.

Nice catch!

> However, the trace entry is now misleading due to this inaccuracy. It is
> furthermore misleading because it reports the effective function, not
> the originally passed one. Fix that as well.

BTW, the trace lacks subleaf(ECX) info, it's meaning for the the leaf 
does have a subleaf, maybe we'd better add it?

> Fixes: 43561123ab37 ("kvm: x86: Improve emulation of CPUID leaves 0BH and 1FH")
> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> ---
>   arch/x86/kvm/cpuid.c | 6 +++---
>   1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index b1c469446b07..79a738f313f8 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -1000,13 +1000,12 @@ static bool cpuid_function_in_range(struct kvm_vcpu *vcpu, u32 function)
>   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 = *eax, function = *eax, index = *ecx;
>   	struct kvm_cpuid_entry2 *entry;
>   	struct kvm_cpuid_entry2 *max;
>   	bool found;
> 
>   	entry = kvm_find_cpuid_entry(vcpu, function, index);
> -	found = entry;
>   	/*
>   	 * Intel CPUID semantics treats any query for an out-of-range
>   	 * leaf as if the highest basic leaf (i.e. CPUID.0H:EAX) were
> @@ -1049,7 +1048,8 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx,
>   			}
>   		}
>   	}
> -	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, found);
> +	found = entry;
> +	trace_kvm_cpuid(orig_function, *eax, *ebx, *ecx, *edx, found);
>   	return found;
>   }
>   EXPORT_SYMBOL_GPL(kvm_cpuid);
> --
> 2.16.4
>