linux-kernel - Re: [PATCH v2] KVM: x86: Assign correct value to array.maxnent

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Date:   Thu, 4 Jun 2020 18:21:51 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Sean Christopherson <sean.j.christopherson@...el.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Xiaoyao Li <xiaoyao.li@...el.com>
Subject: Re: [PATCH v2] KVM: x86: Assign correct value to array.maxnent

On 04/06/20 17:12, Sean Christopherson wrote:
> On Thu, Jun 04, 2020 at 12:16:36PM +0800, Xiaoyao Li wrote:
>> Delay the assignment of array.maxnent to use correct value for the case
>> cpuid->nent > KVM_MAX_CPUID_ENTRIES.
>>
>> Fixes: e53c95e8d41e ("KVM: x86: Encapsulate CPUID entries and metadata in struct")
>> Signed-off-by: Xiaoyao Li <xiaoyao.li@...el.com>
>> ---
>> v2:
>>    - remove "const" of maxnent to fix build error.
>> ---
>>  arch/x86/kvm/cpuid.c | 5 +++--
>>  1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
>> index 253b8e875ccd..3d88ddf781d0 100644
>> --- a/arch/x86/kvm/cpuid.c
>> +++ b/arch/x86/kvm/cpuid.c
>> @@ -426,7 +426,7 @@ EXPORT_SYMBOL_GPL(kvm_set_cpu_caps);
>>  
>>  struct kvm_cpuid_array {
>>  	struct kvm_cpuid_entry2 *entries;
>> -	const int maxnent;
>> +	int maxnent;
>>  	int nent;
>>  };
>>  
>> @@ -870,7 +870,6 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>>  
>>  	struct kvm_cpuid_array array = {
>>  		.nent = 0,
>> -		.maxnent = cpuid->nent,
>>  	};
>>  	int r, i;
>>  
>> @@ -887,6 +886,8 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
>>  	if (!array.entries)
>>  		return -ENOMEM;
>>  
>> +	array.maxnent = cpuid->nent;
> 
> Eh, I'd vote to just do:
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 253b8e875ccd..1e5b1ee75a76 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -870,7 +870,7 @@ int kvm_dev_ioctl_get_cpuid(struct kvm_cpuid2 *cpuid,
> 
>         struct kvm_cpuid_array array = {
>                 .nent = 0,
> -               .maxnent = cpuid->nent,
> +               .maxnent = min(cpuid->nent, (u32)KVM_MAX_CPUID_ENTRIES),
>         };
>         int r, i;
> 

Both are fine, I've queued Xiaoyao's patch.

Paolo