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

[Julien Grall <julien@xxxxxxx>]

On 16/09/2020 10:09, Paul Durrant wrote:
> > -----Original Message-----
> > From: Julien Grall <julien@xxxxxxx>
> > Sent: 16 September 2020 10:07
> > To: Jan Beulich <jbeulich@xxxxxxxx>; Oleksandr Tyshchenko <olekstysh@xxxxxxxxx>
> > Cc: xen-devel@xxxxxxxxxxxxxxxxxxxx; Oleksandr Tyshchenko 
> > <oleksandr_tyshchenko@xxxxxxxx>; Paul Durrant
> > <paul@xxxxxxx>; Stefano Stabellini <sstabellini@xxxxxxxxxx>; Julien Grall 
> > <jgrall@xxxxxxxxxx>
> > Subject: Re: [PATCH V1 14/16] xen/ioreq: Use guest_cmpxchg64() instead of 
> > cmpxchg()
> >
> >
> >
> > 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.
> When using magic pages they should be punched out of the P2M by the time the 
> code gets here, so the memory should not be guest-visible.
Can you point me to the code that doing this?

Cheers,

--
Julien Grall