linux-kernel - Re: [PATCH v2 2/3] KVM: x86: Allocate kvm_vmx/kvm

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Message-ID: <20250416182437.GA963080.vipinsh@google.com>
Date: Wed, 16 Apr 2025 11:24:37 -0700
From: Vipin Sharma <vipinsh@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/3] KVM: x86: Allocate kvm_vmx/kvm_svm structures
 using kzalloc()

On 2025-04-01 08:57:13, Sean Christopherson wrote:
> Now that the size of "struct kvm" is less than 2KiB, switch back to using
> kzalloc() to allocate the VM structures.  Add compile-time assertions in
> vendor code to ensure the size is an order-0 allocation, i.e. to prevent
> unknowingly letting the size balloon in the future.
> 
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  arch/x86/kvm/svm/svm.c          | 1 +
>  arch/x86/kvm/vmx/vmx.c          | 1 +
>  3 files changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index e523d7d8a107..6c7fd7db6f11 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -1940,7 +1940,7 @@ void kvm_x86_vendor_exit(void);
>  #define __KVM_HAVE_ARCH_VM_ALLOC
>  static inline struct kvm *kvm_arch_alloc_vm(void)
>  {
> -	return __vmalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT | __GFP_ZERO);
> +	return kzalloc(kvm_x86_ops.vm_size, GFP_KERNEL_ACCOUNT);
>  }
>  
>  #define __KVM_HAVE_ARCH_VM_FREE
> diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
> index 8abeab91d329..589adc5f92e0 100644
> --- a/arch/x86/kvm/svm/svm.c
> +++ b/arch/x86/kvm/svm/svm.c
> @@ -5536,6 +5536,7 @@ static int __init svm_init(void)
>  	if (r)
>  		goto err_kvm_init;
>  
> +	BUILD_BUG_ON(get_order(sizeof(struct kvm_svm) != 0));

There is a typo here. It is checking sizeof(struct kvm_svm) != 0, instead
of checking get_order(...) != 0.

>  	return 0;
>  
>  err_kvm_init:
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b70ed72c1783..01264842bf45 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -8755,6 +8755,7 @@ static int __init vmx_init(void)
>  	if (r)
>  		goto err_kvm_init;
>  
> +	BUILD_BUG_ON(get_order(sizeof(struct kvm_vmx) != 0));

Same as above.

>  	return 0;
>  
>  err_kvm_init:
> -- 
> 2.49.0.472.ge94155a9ec-goog
>