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 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.

Jan

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