Re: [Xen-devel] [PATCH v3 3/6] x86 / pv: do not treat PGC_extra pages as RAM when constructing dom0

[Jan Beulich <jbeulich@xxxxxxxx>]

On 06.03.2020 14:45, Paul Durrant wrote:
>> -----Original Message-----
>> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan 
>> Beulich
>> Sent: 06 March 2020 13:39
>> To: Durrant, Paul <pdurrant@xxxxxxxxxxxx>
>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Andrew Cooper 
>> <andrew.cooper3@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>;
>> pdurrant@xxxxxxxx; Roger Pau Monné <roger.pau@xxxxxxxxxx>
>> Subject: Re: [Xen-devel] [PATCH v3 3/6] x86 / pv: do not treat PGC_extra 
>> pages as RAM when
>> constructing dom0
>>
>> On 06.03.2020 13:03, Durrant, Paul wrote:
>>>> -----Original Message-----
>>>> From: Xen-devel <xen-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of Jan 
>>>> Beulich
>>>> Sent: 06 March 2020 11:56
>>>> To: pdurrant@xxxxxxxx
>>>> Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Durrant, Paul <pdurrant@xxxxxxxxxxxx>; 
>>>> Roger Pau Monné
>>>> <roger.pau@xxxxxxxxxx>; Wei Liu <wl@xxxxxxx>; Andrew Cooper 
>>>> <andrew.cooper3@xxxxxxxxxx>
>>>> Subject: Re: [Xen-devel] [PATCH v3 3/6] x86 / pv: do not treat PGC_extra 
>>>> pages as RAM when
>>>> constructing dom0
>>>>
>>>> On 05.03.2020 13:45, pdurrant@xxxxxxxx wrote:
>>>>> --- a/xen/arch/x86/pv/dom0_build.c
>>>>> +++ b/xen/arch/x86/pv/dom0_build.c
>>>>> @@ -792,6 +792,10 @@ int __init dom0_construct_pv(struct domain *d,
>>>>>      {
>>>>>          mfn = mfn_x(page_to_mfn(page));
>>>>>          BUG_ON(SHARED_M2P(get_gpfn_from_mfn(mfn)));
>>>>> +
>>>>> +        if ( page->count_info & PGC_extra )
>>>>> +            continue;
>>>>
>>>> This surely is a pattern, i.e. there are more similar changes to
>>>> make: tboot_gen_domain_integrity() e.g. ignores d->xenpage_list,
>>>> and hence with the goal of converting the shared info page would
>>>> also want adjustment. For dump_numa() it may be less important,
>>>> but it would still look more correct if it too got changed.
>>>> audit_p2m() might apparently complain about such pages (and
>>>> hence might be a problem with the one PGC_extra page VMX domains
>>>> now have). And this is only from me looking at
>>>> page_list_for_each(..., &d->page_list) constructs; who knows
>>>> what else there is.
>>>>
>>>
>>> Those are dealt with by the is_special_page() patch later on I think.
>>
>> Having already looked at that patch as well - I don't think so, no.
>> That one only replaces uses of is_xen_heap_page(), but doesn't add
>> any checks where such uses simply aren't needed because code is
>> looking at ->page_list only.
> 
> Well, I did say:
> 
> "It didn't seem appropriate to use that macro here though since we
> know pages on the page list cannot be xenheap pages."

And I agree and understand.

> i.e. an open coded check here seems like the right thing to do.

Indeed.

> If I've missed other places where I need to account for pages which
> are specifically PGC_extra pages then I'll need to fix them similarly.

Yes please. Thanks.

Jan

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxxx
https://lists.xenproject.org/mailman/listinfo/xen-devel