linux-kernel - Re: [PATCH v1] kvm: x86: Revise guest_fpu xcomp

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Date:   Mon, 8 Feb 2021 07:23:13 -0800
From:   Dave Hansen <dave.hansen@...el.com>
To:     Jing Liu <jing2.liu@...ux.intel.com>, pbonzini@...hat.com
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] kvm: x86: Revise guest_fpu xcomp_bv field

On 2/8/21 8:16 AM, Jing Liu wrote:
> -#define XSTATE_COMPACTION_ENABLED (1ULL << 63)
> -
>  static void fill_xsave(u8 *dest, struct kvm_vcpu *vcpu)
>  {
>  	struct xregs_state *xsave = &vcpu->arch.guest_fpu->state.xsave;
> @@ -4494,7 +4492,8 @@ static void load_xsave(struct kvm_vcpu *vcpu, u8 *src)
>  	/* Set XSTATE_BV and possibly XCOMP_BV.  */
>  	xsave->header.xfeatures = xstate_bv;
>  	if (boot_cpu_has(X86_FEATURE_XSAVES))
> -		xsave->header.xcomp_bv = host_xcr0 | XSTATE_COMPACTION_ENABLED;
> +		xsave->header.xcomp_bv = XCOMP_BV_COMPACTED_FORMAT |
> +					 xfeatures_mask_all;

Are 'host_xcr0' and 'xfeatures_mask_all' really interchangeable?  If so,
shouldn't we just remove 'host_xcr0' everywhere?