linux-kernel - Re: [PATCH v2 15/15] KVM: x86/cpuid: Advertise Arch LBR feature in CPUID

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Message-ID: <41f13d29-b375-da1a-543e-7cfcc052a5ed@gmail.com>
Date:   Thu, 22 Dec 2022 19:03:26 +0800
From:   Like Xu <like.xu.linux@...il.com>
To:     Yang Weijiang <weijiang.yang@...el.com>
Cc:     kan.liang@...ux.intel.com, wei.w.wang@...el.com, seanjc@...gle.com,
        pbonzini@...hat.com, jmattson@...gle.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 15/15] KVM: x86/cpuid: Advertise Arch LBR feature in
 CPUID

On 25/11/2022 12:06 pm, Yang Weijiang wrote:
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 85e3df6217af..60b3c591d462 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -134,6 +134,19 @@ static int kvm_check_cpuid(struct kvm_vcpu *vcpu,
>   		if (vaddr_bits != 48 && vaddr_bits != 57 && vaddr_bits != 0)
>   			return -EINVAL;
>   	}
> +	if (kvm_cpu_cap_has(X86_FEATURE_ARCH_LBR)) {
> +		best = cpuid_entry2_find(entries, nent, 0x1c, 0);
> +		if (best) {
> +			unsigned int eax, ebx, ecx, edx;
> +
> +			/* Reject user-space CPUID if depth is different from host's.*/

Try to verify this in the KVM selftest, as this behavior is different from the host.

> +			cpuid_count(0x1c, 0, &eax, &ebx, &ecx, &edx); > +
> +			if ((eax & 0xff) &&
> +			    (best->eax & 0xff) != BIT(fls(eax & 0xff) - 1))
> +				return -EINVAL;
> +		}
> +	}