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Re: [PATCH] VMX: use a single, global APIC access page
- To: Jan Beulich <jbeulich@xxxxxxxx>, "xen-devel@xxxxxxxxxxxxxxxxxxxx" <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 10 Feb 2021 17:00:18 +0000
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- Cc: Kevin Tian <kevin.tian@xxxxxxxxx>, Julien Grall <julien@xxxxxxx>, Wei Liu <wl@xxxxxxx>, Roger Pau Monné <roger.pau@xxxxxxxxxx>
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On 10/02/2021 16:48, Jan Beulich wrote:
> The address of this page is used by the CPU only to recognize when to
> instead access the virtual APIC page instead. No accesses would ever go
> to this page. It only needs to be present in the (CPU) page tables so
> that address translation will produce its address as result for
> respective accesses.
>
> By making this page global, we also eliminate the need to refcount it,
> or to assign it to any domain in the first place.
>
> Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
How certain are you about this?
It's definitely not true on AMD's AVIC - writes very definitely end up
in the backing page if they miss the APIC registers.
This concern was why we didn't use a global page originally, IIRC.
~Andrew
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