From: Paolo Bonzini <pbonzini@redhat.com>
To: "Mohammed Gamal" <mgamal@redhat.com>,
"Gerd Hoffmann" <kraxel@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>
Cc: Guilherme Piccoli <gpiccoli@canonical.com>,
Pedro Principeza <pedro.principeza@canonical.com>,
Eduardo Habkost <ehabkost@redhat.com>,
kvm@vger.kernel.org, libvir-list@redhat.com,
Dann Frazier <dann.frazier@canonical.com>,
mtosatti@redhat.com,
"Dr. David Alan Gilbert" <dgilbert@redhat.com>,
Christian Ehrhardt <christian.ehrhardt@canonical.com>,
qemu-devel@nongnu.org, Laszlo Ersek <lersek@redhat.com>,
fw@gpiccoli.net, rth@twiddle.net
Subject: Re: [PATCH 2/2] x86/cpu: Handle GUEST_MAXPHYADDR < HOST_MAXPHYADDR for hosts that don't support it
Date: Thu, 9 Jul 2020 12:11:41 +0200 [thread overview]
Message-ID: <2c9ec76e-7cfc-f613-ef9b-cb1e7cc54ade@redhat.com> (raw)
In-Reply-To: <8ed00a46daec6b41e7369123e807342e0ecfe751.camel@redhat.com>
On 09/07/20 11:55, Mohammed Gamal wrote:
>> Ideally we would simply outlaw (3), but it's hard for backward
>> compatibility reasons. Second best solution is a flag somewhere
>> (msr, cpuid, ...) telling the guest firmware "you can use
>> GUEST_MAXPHYADDR, we guarantee it is <= HOST_MAXPHYADDR".
> Problem is GUEST_MAXPHYADDR > HOST_MAXPHYADDR is actually a supported
> configuration on some setups. Namely when memory encryption is enabled
> on AMD CPUs[1].
>
It's not that bad since there's two MAXPHYADDRs, the one in CPUID and
the one computed internally by the kernel. GUEST_MAXPHYADDR greater
than the host CPUID maxphyaddr is never supported.
Paolo
next prev parent reply other threads:[~2020-07-09 10:12 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 [this message]
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
2020-07-10 7:21 ` Paolo Bonzini
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