Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Date:   Fri, 29 Apr 2022 14:42:21 +0000
From:   Sean Christopherson <seanjc@google.com>
To:     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, Maxim Levitsky <mlevitsk@redhat.com>,
        Ben Gardon <bgardon@google.com>,
        David Matlack <dmatlack@google.com>
Subject: Re: [PATCH] KVM: x86/mmu: Do not create SPTEs for GFNs that exceed
 host.MAXPHYADDR
Message-ID: <Ymv5TR76RNvFBQhz@google.com>
References: <20220428233416.2446833-1-seanjc@google.com>
 <337332ca-835c-087c-c99b-92c35ea8dcd3@redhat.com>
 <Ymv1I5ixX1+k8Nst@google.com>
 <20e1e7b1-ece7-e9e7-9085-999f7a916ac2@redhat.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20e1e7b1-ece7-e9e7-9085-999f7a916ac2@redhat.com>
Precedence: bulk

On Fri, Apr 29, 2022, Paolo Bonzini wrote:
> On 4/29/22 16:24, Sean Christopherson wrote:
> > I don't love the divergent memslot behavior, but it's technically correct, so I
> > can't really argue.  Do we want to "officially" document the memslot behavior?
> > 
> 
> I don't know what you mean by officially document,

Something in kvm/api.rst under KVM_SET_USER_MEMORY_REGION.

> but at least I have relied on it to test KVM's MAXPHYADDR=52 cases before
> such hardware existed.  :)

Ah, that's a very good reason to support this for shadow paging.  Maybe throw
something about testing in the changelog?  Without considering the testing angle,
it looks like KVM supports max=52 for !TDP just because it can, because practically
speaking there's unlikely to be a use case for exposing that much memory to a
guest when using shadow paging.