Re: [RFC PATCH V1 04/12] xen/arm: Introduce arch specific bits for IOREQ/DM features

[Jan Beulich <jbeulich@xxxxxxxx>]

On 05.08.2020 01:22, Stefano Stabellini wrote:
> On Mon, 3 Aug 2020, Oleksandr Tyshchenko wrote:
>> --- a/xen/include/asm-arm/p2m.h
>> +++ b/xen/include/asm-arm/p2m.h
>> @@ -385,10 +385,11 @@ static inline int set_foreign_p2m_entry(struct domain 
>> *d, unsigned long gfn,
>>                                          mfn_t mfn)
>>  {
>>      /*
>> -     * NOTE: If this is implemented then proper reference counting of
>> -     *       foreign entries will need to be implemented.
>> +     * XXX: handle properly reference. It looks like the page may not always
>> +     * belong to d.
> 
> Just as a reference, and without taking away anything from the comment,
> I think that QEMU is doing its own internal reference counting for these
> mappings.

Which of course in no way replaces the need to do proper ref counting
in Xen. (Just FAOD, as I'm not sure why you've said what you've said.)

Jan