linux-kernel - Re: [PATCH v5 03/15] KVM: SVM: Disable SEV/SEV-ES if NPT is disabled

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Message-ID: <YIG8Ythi0UIbO+Up@google.com>
Date:   Thu, 22 Apr 2021 18:11:46 +0000
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Wei Huang <wei.huang2@....com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, Borislav Petkov <bp@...e.de>,
        Tom Lendacky <thomas.lendacky@....com>,
        Brijesh Singh <brijesh.singh@....com>
Subject: Re: [PATCH v5 03/15] KVM: SVM: Disable SEV/SEV-ES if NPT is disabled

On Thu, Apr 22, 2021, Paolo Bonzini wrote:
> 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.

How about I fold that into the s/lm_root/pml4_root rename[*]?  I.e. make the
blocking of PML5 a functional change, and the rename an opportunistic change?

[*] https://lkml.kernel.org/r/20210318201131.3242619-1-seanjc@google.com