Mailing List Archive: [PATCH] drm/prime: Unbreak virtgpu dma-buf export

[PATCH] drm/prime: Unbreak virtgpu dma-buf export

Mar 22, 2024, 2:48 PM

Post #1 of 8 (35 views)

From: Rob Clark <robdclark@chromium.org>

virtgpu "vram" GEM objects do not implement obj->get_sg_table(). But
they also don't use drm_gem_map_dma_buf(). In fact they may not even
have guest visible pages. But it is perfectly fine to export and share
with other virtual devices.

Reported-by: Dominik Behr <dbehr@chromium.org>
Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
Signed-off-by: Rob Clark <robdclark@chromium.org>
---
drivers/gpu/drm/drm_prime.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
index 7352bde299d5..64dd6276e828 100644
--- a/drivers/gpu/drm/drm_prime.c
+++ b/drivers/gpu/drm/drm_prime.c
@@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
{
struct drm_gem_object *obj = dma_buf->priv;

- if (!obj->funcs->get_sg_table)
+ /*
+ * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
+ * that implement their own ->map_dma_buf() do not.
+ */
+ if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
+ !obj->funcs->get_sg_table)
return -ENOSYS;

return drm_gem_pin(obj);
--
2.44.0

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

dbehr at chromium

Mar 25, 2024, 3:38 PM

Post #2 of 8 (33 views)

Permalink

It also fixes importing virtgpu blobs into real hardware, for instance
amdgpu for DRI_PRIME rendering.

On Fri, Mar 22, 2024 at 2:48?PM Rob Clark <robdclark@gmail.com> wrote:
>
> From: Rob Clark <robdclark@chromium.org>
>
> virtgpu "vram" GEM objects do not implement obj->get_sg_table(). But
> they also don't use drm_gem_map_dma_buf(). In fact they may not even
> have guest visible pages. But it is perfectly fine to export and share
> with other virtual devices.
>
> Reported-by: Dominik Behr <dbehr@chromium.org>
> Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
> drivers/gpu/drm/drm_prime.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> index 7352bde299d5..64dd6276e828 100644
> --- a/drivers/gpu/drm/drm_prime.c
> +++ b/drivers/gpu/drm/drm_prime.c
> @@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
> {
> struct drm_gem_object *obj = dma_buf->priv;
>
> - if (!obj->funcs->get_sg_table)
> + /*
> + * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
> + * that implement their own ->map_dma_buf() do not.
> + */
> + if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
> + !obj->funcs->get_sg_table)
> return -ENOSYS;
>
> return drm_gem_pin(obj);
> --
> 2.44.0
>

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

robdclark at gmail

Mar 25, 2024, 7:38 PM

Post #3 of 8 (29 views)

Permalink

This is actually a bit concerning.. importing a host page backed
buffer without guest mapping into a passthru device probably doesn't
work and should be rejected earlier.

I do think we should relax the restriction (either taking my patch or
reverting the commit it fixes) until we work this out properly
(because the original patch is a regression), but importing a buffer
without guest pages into a passthru device can't possibly work
properly. Maybe it works by chance if the host buffer is mapped to
the guest, but that is not guaranteed.

BR,
-R

On Mon, Mar 25, 2024 at 3:35?PM Dominik Behr <dbehr@chromium.org> wrote:
>
> It also fixes importing virtgpu blobs into real hardware, for instance amdgpu for DRI_PRIME rendering.
>
> On Fri, Mar 22, 2024 at 2:48?PM Rob Clark <robdclark@gmail.com> wrote:
>>
>> From: Rob Clark <robdclark@chromium.org>
>>
>> virtgpu "vram" GEM objects do not implement obj->get_sg_table(). But
>> they also don't use drm_gem_map_dma_buf(). In fact they may not even
>> have guest visible pages. But it is perfectly fine to export and share
>> with other virtual devices.
>>
>> Reported-by: Dominik Behr <dbehr@chromium.org>
>> Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
>> Signed-off-by: Rob Clark <robdclark@chromium.org>
>> ---
>> drivers/gpu/drm/drm_prime.c | 7 ++++++-
>> 1 file changed, 6 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
>> index 7352bde299d5..64dd6276e828 100644
>> --- a/drivers/gpu/drm/drm_prime.c
>> +++ b/drivers/gpu/drm/drm_prime.c
>> @@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
>> {
>> struct drm_gem_object *obj = dma_buf->priv;
>>
>> - if (!obj->funcs->get_sg_table)
>> + /*
>> + * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
>> + * that implement their own ->map_dma_buf() do not.
>> + */
>> + if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
>> + !obj->funcs->get_sg_table)
>> return -ENOSYS;
>>
>> return drm_gem_pin(obj);
>> --
>> 2.44.0
>>

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

contact at emersion

Mar 26, 2024, 2:15 AM

Post #4 of 8 (28 views)

Permalink

Makes sense to me!

Reviewed-by: Simon Ser <contact@emersion.fr>

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

dbehr at google

Mar 27, 2024, 4:15 PM

Post #5 of 8 (27 views)

Permalink

It is mapped, via iommu interface (vfio-iommu) when map_dma is called.
--
Dominik

On Mon, Mar 25, 2024 at 7:38?PM Rob Clark <robdclark@gmail.com> wrote:
>
> This is actually a bit concerning.. importing a host page backed
> buffer without guest mapping into a passthru device probably doesn't
> work and should be rejected earlier.
>
> I do think we should relax the restriction (either taking my patch or
> reverting the commit it fixes) until we work this out properly
> (because the original patch is a regression), but importing a buffer
> without guest pages into a passthru device can't possibly work
> properly. Maybe it works by chance if the host buffer is mapped to
> the guest, but that is not guaranteed.
>
> BR,
> -R
>
> On Mon, Mar 25, 2024 at 3:35?PM Dominik Behr <dbehr@chromium.org> wrote:
> >
> > It also fixes importing virtgpu blobs into real hardware, for instance amdgpu for DRI_PRIME rendering.
> >
> > On Fri, Mar 22, 2024 at 2:48?PM Rob Clark <robdclark@gmail.com> wrote:
> >>
> >> From: Rob Clark <robdclark@chromium.org>
> >>
> >> virtgpu "vram" GEM objects do not implement obj->get_sg_table(). But
> >> they also don't use drm_gem_map_dma_buf(). In fact they may not even
> >> have guest visible pages. But it is perfectly fine to export and share
> >> with other virtual devices.
> >>
> >> Reported-by: Dominik Behr <dbehr@chromium.org>
> >> Fixes: 207395da5a97 ("drm/prime: reject DMA-BUF attach when get_sg_table is missing")
> >> Signed-off-by: Rob Clark <robdclark@chromium.org>
> >> ---
> >> drivers/gpu/drm/drm_prime.c | 7 ++++++-
> >> 1 file changed, 6 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/gpu/drm/drm_prime.c b/drivers/gpu/drm/drm_prime.c
> >> index 7352bde299d5..64dd6276e828 100644
> >> --- a/drivers/gpu/drm/drm_prime.c
> >> +++ b/drivers/gpu/drm/drm_prime.c
> >> @@ -582,7 +582,12 @@ int drm_gem_map_attach(struct dma_buf *dma_buf,
> >> {
> >> struct drm_gem_object *obj = dma_buf->priv;
> >>
> >> - if (!obj->funcs->get_sg_table)
> >> + /*
> >> + * drm_gem_map_dma_buf() requires obj->get_sg_table(), but drivers
> >> + * that implement their own ->map_dma_buf() do not.
> >> + */
> >> + if ((dma_buf->ops->map_dma_buf == drm_gem_map_dma_buf) &&
> >> + !obj->funcs->get_sg_table)
> >> return -ENOSYS;
> >>
> >> return drm_gem_pin(obj);
> >> --
> >> 2.44.0
> >>

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

robdclark at gmail

Mar 28, 2024, 11:47 AM

Post #6 of 8 (23 views)

Permalink

On Tue, Mar 26, 2024 at 2:15?AM Simon Ser <contact@emersion.fr> wrote:
>
> Makes sense to me!
>
> Reviewed-by: Simon Ser <contact@emersion.fr>

Thanks.. any chance I could talk you into pushing to drm-misc-fixes?

BR,
-R

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

contact at emersion

Mar 28, 2024, 11:54 AM

Post #7 of 8 (23 views)

Permalink

On Thursday, March 28th, 2024 at 19:47, Rob Clark <robdclark@gmail.com> wrote:

> any chance I could talk you into pushing to drm-misc-fixes?

Oh sorry, I thought you had access… Pushed with a minor edit to remove
unnecessary parentheses to make checkpatch happy!

Re: [PATCH] drm/prime: Unbreak virtgpu dma-buf export [ In reply to ]

robdclark at gmail

Mar 28, 2024, 11:59 AM

Post #8 of 8 (23 views)

Permalink

On Thu, Mar 28, 2024 at 11:54?AM Simon Ser <contact@emersion.fr> wrote:
>
> On Thursday, March 28th, 2024 at 19:47, Rob Clark <robdclark@gmail.com> wrote:
>
> > any chance I could talk you into pushing to drm-misc-fixes?
>
> Oh sorry, I thought you had access… Pushed with a minor edit to remove
> unnecessary parentheses to make checkpatch happy!

Thanks!

BR,
-R