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Date: Wed, 10 Aug 2016 09:49:02 +0800
From: Peter Xu <peterx@redhat.com>
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Subject: Re: [Qemu-devel] [V15 3/4] hw/i386: Introduce AMD IOMMU
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To: David Kiarie <davidkiarie4@gmail.com>
Cc: QEMU Developers <qemu-devel@nongnu.org>, rkrcmar@redhat.com, Jan Kiszka <jan.kiszka@web.de>, Valentine Sinitsyn <valentine.sinitsyn@gmail.com>, Eduardo Habkost <ehabkost@redhat.com>, "Michael S. Tsirkin" <mst@redhat.com>

On Tue, Aug 09, 2016 at 08:46:09PM +0300, David Kiarie wrote:
> On Tue, Aug 9, 2016 at 8:44 AM, Peter Xu <peterx@redhat.com> wrote:
> 
> > On Tue, Aug 02, 2016 at 11:39:06AM +0300, David Kiarie wrote:
> >
> > [...]
> >
> > > +/* external write */
> > > +static void amdvi_writew(AMDVIState *s, hwaddr addr, uint16_t val)
> > > +{
> > > +    uint16_t romask = lduw_le_p(&s->romask[addr]);
> > > +    uint16_t w1cmask = lduw_le_p(&s->w1cmask[addr]);
> > > +    uint16_t oldval = lduw_le_p(&s->mmior[addr]);
> > > +    stw_le_p(&s->mmior[addr], (val & ~(val & w1cmask)) | (romask &
> > oldval));
> >
> > I think the above is problematic, e.g., what if we write 1 to one of
> > the romask while it's 0 originally? In that case, the RO bit will be
> > written to 1.
> >
> > Maybe we need:
> >
> >   stw_le_p(&s->mmior[addr], ((oldval & romask) | (val & ~romask)) & \
> >                             (val & w1cmask));
> >
> > Same question to the below two functions.
> >
> 
> It seems to me you're not taking care of w1/c bits correctly ?
> 
> I think:
> 
> stw_le_p(&s->mmior[addr], ((oldval & romask) | (val & ~romask)) & \
>                            ~ (val & w1cmask));
> should suffice.

Right. :)

-- peterx