Re: [PATCH v4] VMX: use a single, global APIC access page

[Jan Beulich <jbeulich@xxxxxxxx>]

On 13.04.2021 12:18, Roger Pau Monné wrote:
> On Tue, Apr 13, 2021 at 11:24:09AM +0200, Jan Beulich wrote:
>> On 12.04.2021 17:31, Roger Pau Monné wrote:
>>> On Mon, Apr 12, 2021 at 12:40:48PM +0200, Jan Beulich wrote:
>>>> +    {
>>>> +        const struct page_info *pg = mfn_to_page(mfn);
>>>> +
>>>> +        if ( !page_get_owner(pg) && (pg->count_info & PGC_extra) )
>>>> +        {
>>>> +            ASSERT(type == p2m_mmio_direct);
>>>> +            return 0;
>>>
>>> Are there any other pages that could pass this check? I don't think
>>> so, but wanted to assert.
>>
>> "Normal" extra pages have an owner, so no, there aren't any others.
>> If and when any appear, this may need further customizing, albeit
>> generally I'd hope further pages matching this pattern would also
>> want similar treatment.
> 
> I wonder whether we want to add an assert here to make sure only the
> APIC access page receives this special handling by the shadow code,
> but maybe that's a bit too much?

I think so, yes: It would require either a separate function or
making the variable global. Both feel like a layering violation.

Jan