From: Paolo Bonzini <pbonzini@redhat.com>
To: Eduardo Habkost <ehabkost@redhat.com>
Cc: "Guilherme Piccoli" <gpiccoli@canonical.com>,
"Pedro Principeza" <pedro.principeza@canonical.com>,
"kvm list" <kvm@vger.kernel.org>,
libvir-list@redhat.com,
"Dann Frazier" <dann.frazier@canonical.com>,
rth@twiddle.net, mtosatti@redhat.com,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
"Christian Ehrhardt" <christian.ehrhardt@canonical.com>,
qemu-devel@nongnu.org, "Gerd Hoffmann" <kraxel@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>,
"Mohammed Gamal" <mgamal@redhat.com>,
"Laszlo Ersek" <lersek@redhat.com>,
fw@gpiccoli.net, "Jim Mattson" <jmattson@google.com>
Subject: Re: [PATCH 2/2] x86/cpu: Handle GUEST_MAXPHYADDR < HOST_MAXPHYADDR for hosts that don't support it
Date: Fri, 10 Jul 2020 18:49:31 +0200 [thread overview]
Message-ID: <654ac020-5f6b-9d71-a84f-9c435f5aa0cf@redhat.com> (raw)
In-Reply-To: <20200710160219.GQ780932@habkost.net>
On 10/07/20 18:02, Eduardo Habkost wrote:
> On Fri, Jul 10, 2020 at 09:22:42AM +0200, Paolo Bonzini wrote:
>> On 09/07/20 21:13, Eduardo Habkost wrote:
>>>> Doesn't this require intercepting MOV-to-CR3 when the guest is in PAE
>>>> mode, so that the hypervisor can validate the high bits in the PDPTEs?
>>> If the fix has additional overhead, is the additional overhead
>>> bad enough to warrant making it optional? Most existing
>>> GUEST_MAXPHYADDR < HOST_MAXPHYADDR guests already work today
>>> without the fix.
>>
>> The problematic case is when host maxphyaddr is 52. That case wouldn't
>> work at all without the fix.
>
> What can QEMU do to do differentiate "can't work at all without
> the fix" from "not the best idea, but will probably work"?
Blocking guest_maxphyaddr < host_maxphyaddr if maxphyaddr==52 would be a
good start. However it would block the default configuration on IceLake
processors (which is why Mohammed looked at this thing in the first place).
Paolo
next prev parent reply other threads:[~2020-07-10 16:50 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-19 15:53 [PATCH 0/2] kvm: x86/cpu: Support guest MAXPHYADDR < host MAXPHYADDR Mohammed Gamal
2020-06-19 15:53 ` [PATCH 1/2] kvm: Add support for KVM_CAP_HAS_SMALLER_MAXPHYADDR Mohammed Gamal
2020-06-19 15:53 ` [PATCH 2/2] x86/cpu: Handle GUEST_MAXPHYADDR < HOST_MAXPHYADDR for hosts that don't support it Mohammed Gamal
2020-06-19 16:25 ` Paolo Bonzini
2020-07-08 17:16 ` Eduardo Habkost
2020-07-08 17:26 ` Daniel P. Berrangé
2020-07-09 9:44 ` Gerd Hoffmann
2020-07-09 9:55 ` Mohammed Gamal
2020-07-09 10:11 ` Paolo Bonzini
2020-07-09 17:00 ` Jim Mattson
2020-07-09 19:13 ` Eduardo Habkost
2020-07-10 7:22 ` Paolo Bonzini
2020-07-10 16:02 ` Eduardo Habkost
2020-07-10 16:49 ` Paolo Bonzini [this message]
2020-07-10 7:21 ` Paolo Bonzini
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