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Re: [PATCH v4] x86: add etc/phys-bits fw_cfg file
From: |
Gerd Hoffmann |
Subject: |
Re: [PATCH v4] x86: add etc/phys-bits fw_cfg file |
Date: |
Fri, 23 Sep 2022 08:23:12 +0200 |
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