Re: [Xen-devel] [PATCH v8 1/5] x86/p2m: Allow p2m_get_page_from_gfn to return shared entries

[Jan Beulich <jbeulich@xxxxxxxx>]

On 11.02.2020 11:29, Tamas K Lengyel wrote:
> On Tue, Feb 11, 2020 at 2:17 AM Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>
>> On 10.02.2020 20:21, Tamas K Lengyel wrote:
>>> The owner domain of shared pages is dom_cow, use that for get_page
>>> otherwise the function fails to return the correct page under some
>>> situations. The check if dom_cow should be used was only performed in
>>> a subset of use-cases. Fixing the error and simplifying the existing check
>>> since we can't have any shared entries with dom_cow being NULL.
>>>
>>> Signed-off-by: Tamas K Lengyel <tamas.lengyel@xxxxxxxxx>
>>
>> I find it quite disappointing that the blank lines requested to be
>> added ...
>>
>>> --- a/xen/arch/x86/mm/p2m.c
>>> +++ b/xen/arch/x86/mm/p2m.c
>>> @@ -574,11 +574,12 @@ struct page_info *p2m_get_page_from_gfn(
>>>                  if ( fdom == NULL )
>>>                      page = NULL;
>>>              }
>>> -            else if ( !get_page(page, p2m->domain) &&
>>> -                      /* Page could be shared */
>>> -                      (!dom_cow || !p2m_is_shared(*t) ||
>>> -                       !get_page(page, dom_cow)) )
>>> -                page = NULL;
>>> +            else
>>> +            {
>>> +                struct domain *d = !p2m_is_shared(*t) ? p2m->domain : 
>>> dom_cow;
>>> +                if ( !get_page(page, d) )
>>
>> .. above here and ...
>>
>>> @@ -594,8 +595,9 @@ struct page_info *p2m_get_page_from_gfn(
>>>      mfn = get_gfn_type_access(p2m, gfn_x(gfn), t, a, q, NULL);
>>>      if ( p2m_is_ram(*t) && mfn_valid(mfn) )
>>>      {
>>> +        struct domain *d = !p2m_is_shared(*t) ? p2m->domain : dom_cow;
>>>          page = mfn_to_page(mfn);
>>
>> ... above here still haven't appeared. No matter that it's easy to
>> do so while committing, when you send a new version you should
>> really address such remarks yourself, I think.
> 
> Noted. I haven't addressed it since it appeared to me that this patch
> has been ready to go in for like 3 revisions already as-is given the
> blank-lines were non-blockers.

The patch continues to lack a maintainer ack. Hence it hasn't been
ready to go in at any point in time.

Jan

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