From: "Michael S. Tsirkin" <mst@redhat.com>
To: Gerd Hoffmann <kraxel@redhat.com>
Cc: "Paolo Bonzini" <pbonzini@redhat.com>,
"Daniel P. Berrangé" <berrange@redhat.com>,
qemu-devel <qemu-devel@nongnu.org>,
"Sergio Lopez" <slp@redhat.com>,
"Eduardo Habkost" <eduardo@habkost.net>,
"Marcel Apfelbaum" <marcel.apfelbaum@gmail.com>,
"Richard Henderson" <richard.henderson@linaro.org>,
kvm <kvm@vger.kernel.org>,
"Marcelo Tosatti" <mtosatti@redhat.com>
Subject: Re: [PATCH v4] x86: add etc/phys-bits fw_cfg file
Date: Fri, 7 Oct 2022 09:44:42 -0400 [thread overview]
Message-ID: <20221007094427-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <20220923062312.sibqhfhfznnc22km@sirius.home.kraxel.org>
On Fri, Sep 23, 2022 at 08:23:12AM +0200, Gerd Hoffmann wrote:
> Hi,
>
> > > Given newer processors have more than 40 and for older ones we know
> > > the possible values for the two relevant x86 vendors we could do
> > > something along the lines of:
> > >
> > > phys-bits >= 41 -> valid
> > > phys-bits == 40 + AuthenticAMD -> valid
> > > phys-bits == 36,39 + GenuineIntel -> valid
> > > everything else -> invalid
> > >
> > > Does that look sensible to you?
> > >
> >
> > Yes, it does! Is phys-bits == 36 the same as invalid?
>
> 'invalid' would continue to use the current guesswork codepath for
> phys-bits. Which will end up with phys-bits = 36 for smaller VMs, but
> it can go beyond that in VMs with alot (32G or more) of memory. That
> logic assumes that physical machines with enough RAM for 32G+ guests
> have a physical address space > 64G.
>
> 'phys-bits = 36' would be a hard limit.
>
> So, it's not exactly the same but small VMs wouldn't see a difference.
>
> take care,
> Gerd
I dropped the patch for now.
--
MST
next prev parent reply other threads:[~2022-10-07 15:24 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-22 10:14 [PATCH v4] x86: add etc/phys-bits fw_cfg file Gerd Hoffmann
2022-09-22 11:24 ` Daniel P. Berrangé
2022-09-22 11:56 ` Michael S. Tsirkin
2022-09-22 12:20 ` Gerd Hoffmann
2022-09-22 12:38 ` Paolo Bonzini
2022-09-22 14:16 ` Gerd Hoffmann
2022-09-22 17:13 ` Jim Mattson
2022-09-22 19:49 ` Paolo Bonzini
2022-09-22 20:33 ` Gerd Hoffmann
2022-09-23 6:00 ` Paolo Bonzini
2022-09-23 6:23 ` Gerd Hoffmann
2022-10-07 13:44 ` Michael S. Tsirkin [this message]
2022-10-10 7:30 ` Gerd Hoffmann
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