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Subject: Re: [PATCH 0/7] KVM: x86: guest MAXPHYADDR and C-bit fixes
From:   Tom Lendacky <thomas.lendacky@amd.com>
To:     Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Cc:     Vitaly Kuznetsov <vkuznets@redhat.com>,
        Wanpeng Li <wanpengli@tencent.com>,
        Jim Mattson <jmattson@google.com>,
        Joerg Roedel <joro@8bytes.org>, kvm@vger.kernel.org,
        linux-kernel@vger.kernel.org, Peter Gonda <pgonda@google.com>,
        Brijesh Singh <brijesh.singh@amd.com>
References: <20210623230552.4027702-1-seanjc@google.com>
 <324a95ee-b962-acdf-9bd7-b8b23b9fb991@amd.com>
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Date:   Thu, 24 Jun 2021 11:36:37 -0500
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> 
> Here's an explanation of the physical address reduction for bare-metal and
> guest.
> 
> With MSR 0xC001_0010[SMEE] = 0:
>   No reduction in host or guest max physical address.
> 
> With MSR 0xC001_0010[SMEE] = 1:
> - Reduction in the host is enumerated by CPUID 0x8000_001F_EBX[11:6],
>   regardless of whether SME is enabled in the host or not. So, for example
>   on EPYC generation 2 (Rome) you would see a reduction from 48 to 43.
> - There is no reduction in physical address in a legacy guest (non-SEV
>   guest), so the guest can use a 48-bit physical address
> - There is a reduction of only the encryption bit in an SEV guest, so
>   the guest can use up to a 47-bit physical address. This is why the
>   Qemu command line sev-guest option uses a value of 1 for the
>   "reduced-phys-bits" parameter.
> 

The guest statements all assume that NPT is enabled.

Thanks,
Tom