linux-kernel - Re: [PATCH v5 17/19] KVM:x86: Enable guest CET supervisor xstate bit support

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Message-ID: <3075190f-d8a5-0d7d-56e9-671a2052d20f@redhat.com>
Date:   Sat, 5 Aug 2023 00:02:28 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Yang Weijiang <weijiang.yang@...el.com>, seanjc@...gle.com,
        peterz@...radead.org, john.allen@....com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     rick.p.edgecombe@...el.com, chao.gao@...el.com,
        binbin.wu@...ux.intel.com
Subject: Re: [PATCH v5 17/19] KVM:x86: Enable guest CET supervisor xstate bit
 support

On 8/3/23 06:27, Yang Weijiang wrote:
>   	if (boot_cpu_has(X86_FEATURE_XSAVES)) {
> +		u32 eax, ebx, ecx, edx;
> +
> +		cpuid_count(0xd, 1, &eax, &ebx, &ecx, &edx);
>   		rdmsrl(MSR_IA32_XSS, host_xss);
>   		kvm_caps.supported_xss = host_xss & KVM_SUPPORTED_XSS;
> +		if (ecx & XFEATURE_MASK_CET_KERNEL)
> +			kvm_caps.supported_xss |= XFEATURE_MASK_CET_KERNEL;
>   	}

This is a bit hackish and makes me lean more towards adding support for 
XFEATURE_MASK_CET_KERNEL in host MSR_IA32_XSS (and then possibly hide it 
in the actual calls to XSAVE/XRSTORS for non-guest FPU).

Paolo