linux-kernel - Re: [PATCH 15/19] kvm: x86: Save and restore guest XFD

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Message-ID: <97814bdf-2e58-2823-ca55-30b2447af3f1@redhat.com>
Date:   Fri, 10 Dec 2021 23:01:15 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Zhong <yang.zhong@...el.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com
Cc:     seanjc@...gle.com, jun.nakajima@...el.com, kevin.tian@...el.com,
        jing2.liu@...ux.intel.com, jing2.liu@...el.com
Subject: Re: [PATCH 15/19] kvm: x86: Save and restore guest XFD_ERR properly

On 12/8/21 01:03, Yang Zhong wrote:
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -219,6 +219,11 @@ static void kvm_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
>   		kvm_apic_set_version(vcpu);
>   	}
>   
> +	/* Enable saving guest XFD_ERR */
> +	best = kvm_find_cpuid_entry(vcpu, 7, 0);
> +	if (best && cpuid_entry_has(best, X86_FEATURE_AMX_TILE))
> +		vcpu->arch.guest_fpu.xfd_err = 0;
> +

This is incorrect.  Instead it should check whether leaf 0xD includes 
any dynamic features.

Paolo