linux-kernel - Re: [PATCH v4 1/7] hyperv: Detect Nested virtualization support for SVM

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Message-ID: <20210428140156.flf5ie6r2j7os5ch@liuwe-devbox-debian-v2>
Date:   Wed, 28 Apr 2021 14:01:56 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Vineeth Pillai <viremana@...ux.microsoft.com>
Cc:     Lan Tianyu <Tianyu.Lan@...rosoft.com>,
        Michael Kelley <mikelley@...rosoft.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Wei Liu <wei.liu@...nel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "K. Y. Srinivasan" <kys@...rosoft.com>, x86@...nel.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org
Subject: Re: [PATCH v4 1/7] hyperv: Detect Nested virtualization support for
 SVM

On Tue, Apr 27, 2021 at 08:54:50PM +0000, Vineeth Pillai wrote:
> Previously, to detect nested virtualization enlightenment support,
> we were using HV_X64_ENLIGHTENED_VMCS_RECOMMENDED feature bit of
> HYPERV_CPUID_ENLIGHTMENT_INFO.EAX CPUID as docuemented in TLFS:
>  "Bit 14: Recommend a nested hypervisor using the enlightened VMCS
>   interface. Also indicates that additional nested enlightenments
>   may be available (see leaf 0x4000000A)".
> 
> Enlightened VMCS, however, is an Intel only feature so the above
> detection method doesn't work for AMD. So, use the
> HYPERV_CPUID_VENDOR_AND_MAX_FUNCTIONS.EAX CPUID information ("The
> maximum input value for hypervisor CPUID information.") and this
> works for both AMD and Intel.
> 
> Signed-off-by: Vineeth Pillai <viremana@...ux.microsoft.com>

Acked-by: Wei Liu <wei.liu@...nel.org>