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

[Oleksandr <olekstysh@xxxxxxxxx>]

On 16.09.20 12:12, Julien Grall wrote:

Hi all.

> 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,
If we are not going to use legacy interface on Arm we will have a page 
to be mapped in a single domain at the time.
I will update patch to use "s->emulator" if no objections.


--
Regards,

Oleksandr Tyshchenko