linux-kernel - Re: [PATCH v4 18/21] kvm: x86: Add support for getting/setting expanded xstate buffer

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Date:   Tue, 4 Jan 2022 19:46:20 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Yang Zhong <yang.zhong@...el.com>
Cc:     x86@...nel.org, kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-kselftest@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com, pbonzini@...hat.com, corbet@....net,
        shuah@...nel.org, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com,
        guang.zeng@...el.com, wei.w.wang@...el.com
Subject: Re: [PATCH v4 18/21] kvm: x86: Add support for getting/setting
 expanded xstate buffer

On Wed, Dec 29, 2021, Yang Zhong wrote:
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index bdf89c28d2ce..76e1941db223 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4296,6 +4296,11 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>  		else
>  			r = 0;
>  		break;
> +	case KVM_CAP_XSAVE2:
> +		r = kvm->vcpus[0]->arch.guest_fpu.uabi_size;

a) This does not compile against kvm/queue.

   arch/x86/kvm/x86.c: In function ‘kvm_vm_ioctl_check_extension’:
   arch/x86/kvm/x86.c:4317:24: error: ‘struct kvm’ has no member named ‘vcpus’
    4317 |                 r = kvm->vcpus[0]->arch.guest_fpu.uabi_size;

b) vcpu0 is not guaranteed to be non-NULL at this point.

> +		if (r < sizeof(struct kvm_xsave))
> +			r = sizeof(struct kvm_xsave);
> +		break;
>  	default:
>  		break;
>  	}