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Subject: Re: [PATCH v5 03/15] KVM: SVM: Disable SEV/SEV-ES if NPT is disabled
To:     Sean Christopherson <seanjc@google.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Wei Huang <wei.huang2@amd.com>,
        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, Borislav Petkov <bp@suse.de>,
        Tom Lendacky <thomas.lendacky@amd.com>,
        Brijesh Singh <brijesh.singh@amd.com>
References: <20210422021125.3417167-1-seanjc@google.com>
 <20210422021125.3417167-4-seanjc@google.com>
 <5e8a2d7d-67de-eef4-ab19-33294920f50c@redhat.com>
 <YIGhC/1vlIAZfwzm@google.com>
From:   Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <882d8bb4-8d40-1b4d-0742-4a4f2c307e5b@redhat.com>
Date:   Thu, 22 Apr 2021 19:08:05 +0200
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On 22/04/21 18:15, Sean Christopherson wrote:
>> Support for 5-level page tables on NPT is not hard to fix and could be
>> tested by patching QEMU.  However, the !NPT case would also have to be fixed
>> by extending the PDP and PML4 stacking trick to a PML5.
>   
> Isn't that backwards?  It's the nested NPT case that requires the stacking trick.
> When !NPT is disabled in L0 KVM, 32-bit guests are run with PAE paging.  Maybe
> I'm misunderstanding what you're suggesting.

Yes, you're right.  NPT is easy but we would have to guess what the spec 
would say about MAXPHYADDR, while nNPT would require the stacking of a 
PML5.  Either way, blocking KVM is the easiest thing todo.

Paolo