Re: [Nouveau] [RESEND PATCH 1/3] nouveau: fix migrate page regression

[Ben Skeggs]

On Thu, 25 Jun 2020 at 15:23, Ben Skeggs <skeggsb@xxxxxxxxx> wrote:
>
> On Tue, 23 Jun 2020 at 10:51, John Hubbard <jhubbard@xxxxxxxxxx> wrote:
> >
> > On 2020-06-22 16:38, Ralph Campbell wrote:
> > > The patch to add zero page migration to GPU memory inadvertantly included
> >
> > inadvertently
> >
> > > part of a future change which broke normal page migration to GPU memory
> > > by copying too much data and corrupting GPU memory.
> > > Fix this by only copying one page instead of a byte count.
> > >
> > > Fixes: 9d4296a7d4b3 ("drm/nouveau/nouveau/hmm: fix migrate zero page to GPU")
> > > Signed-off-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/nouveau/nouveau_dmem.c | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/nouveau/nouveau_dmem.c b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > > index e5c230d9ae24..cc9993837508 100644
> > > --- a/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > > +++ b/drivers/gpu/drm/nouveau/nouveau_dmem.c
> > > @@ -550,7 +550,7 @@ static unsigned long nouveau_dmem_migrate_copy_one(struct nouveau_drm *drm,
> > >                                        DMA_BIDIRECTIONAL);
> > >               if (dma_mapping_error(dev, *dma_addr))
> > >                       goto out_free_page;
> > > -             if (drm->dmem->migrate.copy_func(drm, page_size(spage),
> > > +             if (drm->dmem->migrate.copy_func(drm, 1,
> > >                       NOUVEAU_APER_VRAM, paddr, NOUVEAU_APER_HOST, *dma_addr))
> > >                       goto out_dma_unmap;
> > >       } else {
> > >
> >
> >
> > I Am Not A Nouveau Expert, nor is it really clear to me how
> > page_size(spage) came to contain something other than a page's worth of
> > byte count, but this fix looks accurate to me. It's better for
> > maintenance, too, because the function never intends to migrate "some
> > number of bytes". It intends to migrate exactly one page.
> >
> > Hope I'm not missing something fundamental, but:
> I'm actually a bit confused here too.  Because, it *looks* like the
> function takes a byte count, not a page count, and unless I'm missing
> something too, it's setup the copy class for a byte count also.
No, nevermind.. I was looking at nvc0b5_migrate_clear() :)

>
> >
> > Reviewed-by: John Hubbard <jhubbard@xxxxxxxxxx
> >
> >
> > thanks,
> > --
> > John Hubbard
> > NVIDIA
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