Re: [PATCH 1/2] KVM: CPUID: Check limit first when emulating CPUID instruction

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

On Tue, 2019-09-10 at 16:24 +0800, Xiaoyao Li wrote:
> When limit checking is required, it should be executed first, which is
> consistent with the CPUID specification.
> 
> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  arch/x86/kvm/cpuid.c | 50 +++++++++++++++++++++++++-------------------
>  1 file changed, 28 insertions(+), 22 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 22c2720cd948..866546b4d834 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -952,23 +952,33 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct
> kvm_vcpu *vcpu,
>  EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
>  
>  /*
> - * If no match is found, check whether we exceed the vCPU's limit
> - * and return the content of the highest valid _standard_ leaf instead.
> - * This is to satisfy the CPUID specification.
> + * Based on CPUID specification, if leaf number exceeds the vCPU's limit,
> + * it should return the content of the highest valid _standard_ leaf instead.
> + * Note: *found is set true only means the queried leaf number doesn't exceed
> + * the maximum leaf number of basic or extented leaf.
>   */
> -static struct kvm_cpuid_entry2* check_cpuid_limit(struct kvm_vcpu *vcpu,
> -                                                  u32 function, u32 index)
> +static struct kvm_cpuid_entry2* cpuid_check_limit(struct kvm_vcpu *vcpu,
> +                                                  u32 function, u32 index,
> +						  bool *found)
>  {
>  	struct kvm_cpuid_entry2 *maxlevel;
>  
>  	maxlevel = kvm_find_cpuid_entry(vcpu, function & 0x80000000, 0);
> -	if (!maxlevel || maxlevel->eax >= function)
> +	if (!maxlevel)
>  		return NULL;
> -	if (function & 0x80000000) {
> -		maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0);
> -		if (!maxlevel)
> -			return NULL;
> +
> +	if (maxlevel->eax >= function) {
> +		if (found)
> +			*found = true;
> +		return kvm_find_cpuid_entry(vcpu, function, index);
>  	}
> +
> +	if (function & 0x80000000)
> +		maxlevel = kvm_find_cpuid_entry(vcpu, 0, 0);
> +
> +	if (!maxlevel)
> +		return NULL;
> +
>  	return kvm_find_cpuid_entry(vcpu, maxlevel->eax, index);
>  }
>  
> @@ -977,26 +987,22 @@ bool kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32
> *ebx,
>  {
>  	u32 function = *eax, index = *ecx;
>  	struct kvm_cpuid_entry2 *best;
> -	bool entry_found = true;
> +	bool entry_found = false;
>  
> -	best = kvm_find_cpuid_entry(vcpu, function, index);
> +	if (check_limit)
> +		best = cpuid_check_limit(vcpu, function, index, &entry_found);
> +	else
> +		best = kvm_find_cpuid_entry(vcpu, function, index);
>  
> -	if (!best) {
> -		entry_found = false;
> -		if (!check_limit)
> -			goto out;
> -
> -		best = check_cpuid_limit(vcpu, function, index);
> -	}
> -
> -out:
>  	if (best) {
>  		*eax = best->eax;
>  		*ebx = best->ebx;
>  		*ecx = best->ecx;
>  		*edx = best->edx;
> -	} else
> +	} else {
> +		entry_found = false;
>  		*eax = *ebx = *ecx = *edx = 0;
> +	}
>  	trace_kvm_cpuid(function, *eax, *ebx, *ecx, *edx, entry_found);
>  	return entry_found;
>  }

Just realise the entry_found is not set true if found in no limit checking case.
Will send v2.