From: David Stevens <stevensd@chromium.org>
To: "Christian König" <christian.koenig@amd.com>
Cc: ML dri-devel <dri-devel@lists.freedesktop.org>,
Gurchetan Singh <gurchetansingh@chromium.org>
Subject: Re: [PATCH] drm/ttm: use compound pages for THP
Date: Wed, 13 Jan 2021 18:33:17 +0900 [thread overview]
Message-ID: <CAD=HUj4isb5-knjijDj6MqGkk6xSQuXt3uBK8jBy1qtxHM9NZg@mail.gmail.com> (raw)
In-Reply-To: <e0797913-7314-979f-cea8-6af3a67a22a6@amd.com>
On Wed, Jan 13, 2021 at 5:58 PM Christian König
<christian.koenig@amd.com> wrote:
>
> Am 13.01.21 um 09:47 schrieb David Stevens:
> > Compound page metadata is necessary for page reference counting to work
> > properly on pages besides the head page. Without it, put_page
> > corresponding to the last outstanding get_page call on a tail page will
> > end up freeing that page, even if the bo still references the page.
>
> NAK, I should add a comment since I can't count any more how many times
> people came up with this.
>
> Calling put_page() on a TTM allocated page is strictly illegal in the
> first place since they are not reference counted.
>
> Please don't tell me somebody once more tried to mmap() pages from a
> DMA-buf created sg_table into a process address space?
I ran into this on a system using the currently in development
virtio-gpu blob resources [1]. The implementation passes dma buffers
allocated by the host gpu to KVM_SET_USER_MEMORY_REGION, so the guest
can directly access the buffers without the need for an intermediate
copy.
[1] https://patchwork.kernel.org/project/dri-devel/cover/20200814024000.2485-1-gurchetansingh@chromium.org/
> Regards,
> Christian.
>
> >
> > Signed-off-by: David Stevens <stevensd@chromium.org>
> > ---
> > drivers/gpu/drm/ttm/ttm_pool.c | 1 -
> > 1 file changed, 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/ttm/ttm_pool.c b/drivers/gpu/drm/ttm/ttm_pool.c
> > index 7b2f60616750..09239b93dc2c 100644
> > --- a/drivers/gpu/drm/ttm/ttm_pool.c
> > +++ b/drivers/gpu/drm/ttm/ttm_pool.c
> > @@ -83,7 +83,6 @@ static struct page *ttm_pool_alloc_page(struct ttm_pool *pool, gfp_t gfp_flags,
> > gfp_flags |= GFP_TRANSHUGE_LIGHT | __GFP_NORETRY |
> > __GFP_KSWAPD_RECLAIM;
> > gfp_flags &= ~__GFP_MOVABLE;
> > - gfp_flags &= ~__GFP_COMP;
> > }
> >
> > if (!pool->use_dma_alloc) {
>
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next prev parent reply other threads:[~2021-01-14 9:29 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-01-13 8:47 [PATCH] drm/ttm: use compound pages for THP David Stevens
2021-01-13 8:58 ` Christian König
2021-01-13 9:33 ` David Stevens [this message]
2021-01-13 12:44 ` Christian König
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