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Date: Thu, 8 Apr 2021 09:15:47 -0400 From: Vineeth Pillai <viremana@...ux.microsoft.com> To: Vitaly Kuznetsov <vkuznets@...hat.com> Cc: "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, Lan Tianyu <Tianyu.Lan@...rosoft.com>, Michael Kelley <mikelley@...rosoft.com>, Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.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> Subject: Re: [PATCH 1/7] hyperv: Detect Nested virtualization support for SVM Hi Vitaly, On 4/8/21 7:06 AM, Vitaly Kuznetsov wrote: > - if (ms_hyperv.hints & HV_X64_ENLIGHTENED_VMCS_RECOMMENDED) { > + /* > + * AMD does not need enlightened VMCS as VMCB is already a > + * datastructure in memory. > Well, VMCS is also a structure in memory, isn't it? It's just that we > don't have a 'clean field' concept for it and we can't use normal memory > accesses. Yes, you are right. I was referring to the fact that we cant use normal memory accesses, but is a bit mis-worded. > >> We need to get the nested >> + * features if SVM is enabled. >> + */ >> + if (boot_cpu_has(X86_FEATURE_SVM) || >> + ms_hyperv.hints & HV_X64_ENLIGHTENED_VMCS_RECOMMENDED) { > Do I understand correctly that we can just look at CPUID.0x40000000.EAX > and in case it is >= 0x4000000A we can read HYPERV_CPUID_NESTED_FEATURES > leaf? I'd suggest we do that intead then. I agree, that is a better way to consolidate both the cases. Will change it in the next iteration. Probably the above code comment is not needed when we consolidate the cases here. Thanks, Vineeth
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