Re: [PATCH V1 14/16] xen/ioreq: Use guest_cmpxchg64() instead of cmpxchg()

[Julien Grall <julien@xxxxxxx>]

On 16/09/2020 10:04, Jan Beulich wrote:
> On 10.09.2020 22:22, Oleksandr Tyshchenko wrote:
> > @@ -1325,7 +1327,7 @@ static int hvm_send_buffered_ioreq(struct 
> > hvm_ioreq_server *s, ioreq_t *p)
> >   
> >           new.read_pointer = old.read_pointer - n * IOREQ_BUFFER_SLOT_NUM;
> >           new.write_pointer = old.write_pointer - n * IOREQ_BUFFER_SLOT_NUM;
> > -        cmpxchg(&pg->ptrs.full, old.full, new.full);
> > +        guest_cmpxchg64(d, &pg->ptrs.full, old.full, new.full);
> But the memory we're updating is shared with s->emulator, not with d,
> if I'm not mistaken.
It is unfortunately shared with both s->emulator and d when using the 
legacy interface.
For Arm, there is no plan to support the legacy interface, so we should 
s->emulator and we should be fully protected.
Cheers,

--
Julien Grall