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

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Date:   Thu, 4 Jun 2020 08:12:33 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     20200604024304.14643-1-xiaoyao.li@...el.com
Cc:     Paolo Bonzini <pbonzini@...hat.com>, 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 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;



> +
>  	for (i = 0; i < ARRAY_SIZE(funcs); i++) {
>  		r = get_cpuid_func(&array, funcs[i], type);
>  		if (r)
> -- 
> 2.18.2
>