Re: [PATCH] VMX: use a single, global APIC access page

[Jan Beulich <jbeulich@xxxxxxxx>]

On 10.02.2021 18:00, Andrew Cooper wrote:
> 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.

Doesn't this require a per-vCPU page then anyway? With a per-domain
one things can't work correctly in the case you describe.

Jan