* Re: [PATCH] drm/virtio: fix mmap page attributes
2019-12-10 8:57 [PATCH] drm/virtio: fix mmap page attributes Gerd Hoffmann
@ 2019-12-10 9:27 ` Thomas Zimmermann
2019-12-11 8:15 ` Gerd Hoffmann
2019-12-11 1:06 ` Gurchetan Singh
2019-12-12 14:49 ` Ruhl, Michael J
2 siblings, 1 reply; 5+ messages in thread
From: Thomas Zimmermann @ 2019-12-10 9:27 UTC (permalink / raw)
To: Gerd Hoffmann, dri-devel
Cc: David Airlie, open list, open list:VIRTIO GPU DRIVER, gurchetansingh
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Hi
Am 10.12.19 um 09:57 schrieb Gerd Hoffmann:
> virtio-gpu uses cached mappings. shmem helpers use writecombine though.
> So roll our own mmap function, wrapping drm_gem_shmem_mmap(), to tweak
> vm_page_prot accordingly.
>
> Reported-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> drivers/gpu/drm/virtio/virtgpu_object.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 017a9e0fc3bb..158610902054 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -75,6 +75,22 @@ static void virtio_gpu_free_object(struct drm_gem_object *obj)
> drm_gem_shmem_free_object(obj);
> }
>
> +static int virtio_gpu_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> +{
> + pgprot_t prot;
> + int ret;
> +
> + ret = drm_gem_shmem_mmap(obj, vma);
> + if (ret < 0)
> + return ret;
> +
> + /* virtio-gpu needs normal caching, so clear writecombine */
> + prot = vm_get_page_prot(vma->vm_flags);
> + prot = pgprot_decrypted(prot);
> + vma->vm_page_prot = prot;
> + return 0;
> +}
There's similar code in udl, [1] which still uses writecombine for
imported buffers. Virtio does not need this?
Aside from this, do you think we could handle all special cases within
shmem?
Best regards
Thomas
[1]
https://cgit.freedesktop.org/drm/drm-tip/tree/drivers/gpu/drm/udl/udl_gem.c?id=28ecf94a6f1072fc4744c06f5b3d267297125b37#n20
> +
> static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .free = virtio_gpu_free_object,
> .open = virtio_gpu_gem_object_open,
> @@ -86,7 +102,7 @@ static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .get_sg_table = drm_gem_shmem_get_sg_table,
> .vmap = drm_gem_shmem_vmap,
> .vunmap = drm_gem_shmem_vunmap,
> - .mmap = &drm_gem_shmem_mmap,
> + .mmap = &virtio_gpu_gem_mmap,
> };
>
> struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
>
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Felix Imendörffer
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^ permalink raw reply [flat|nested] 5+ messages in thread* Re: [PATCH] drm/virtio: fix mmap page attributes
2019-12-10 9:27 ` Thomas Zimmermann
@ 2019-12-11 8:15 ` Gerd Hoffmann
0 siblings, 0 replies; 5+ messages in thread
From: Gerd Hoffmann @ 2019-12-11 8:15 UTC (permalink / raw)
To: Thomas Zimmermann
Cc: dri-devel, David Airlie, open list, open list:VIRTIO GPU DRIVER,
gurchetansingh
Hi,
> There's similar code in udl, [1] which still uses writecombine for
> imported buffers. Virtio does not need this?
virtio doesn't support dma-buf imports (yet).
So no worries for now.
Why pick writecombine for the imported buffer btw?
It'll probably be correct for the majority of imports, but it still
looks like a educated guess to me. What if you import from vgem?
I guess we should either ...
(1) Ask the exporting driver to handle things, simliar to how it is
done for vmaps already, probably by calling dma_buf_mmap(), or
(2) Refuse to mmap imported objects via drm api.
> Aside from this, do you think we could handle all special cases within
> shmem?
Probably makes sense to teach shmem helpers about caching.
cheers,
Gerd
^ permalink raw reply [flat|nested] 5+ messages in thread
* Re: [PATCH] drm/virtio: fix mmap page attributes
2019-12-10 8:57 [PATCH] drm/virtio: fix mmap page attributes Gerd Hoffmann
2019-12-10 9:27 ` Thomas Zimmermann
@ 2019-12-11 1:06 ` Gurchetan Singh
2019-12-12 14:49 ` Ruhl, Michael J
2 siblings, 0 replies; 5+ messages in thread
From: Gurchetan Singh @ 2019-12-11 1:06 UTC (permalink / raw)
To: Gerd Hoffmann
Cc: ML dri-devel, David Airlie, Daniel Vetter,
open list:VIRTIO GPU DRIVER, open list
On Tue, Dec 10, 2019 at 12:58 AM Gerd Hoffmann <kraxel@redhat.com> wrote:
>
> virtio-gpu uses cached mappings. shmem helpers use writecombine though.
> So roll our own mmap function, wrapping drm_gem_shmem_mmap(), to tweak
> vm_page_prot accordingly.
>
> Reported-by: Gurchetan Singh <gurchetansingh@chromium.org>
> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
> ---
> drivers/gpu/drm/virtio/virtgpu_object.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c b/drivers/gpu/drm/virtio/virtgpu_object.c
> index 017a9e0fc3bb..158610902054 100644
> --- a/drivers/gpu/drm/virtio/virtgpu_object.c
> +++ b/drivers/gpu/drm/virtio/virtgpu_object.c
> @@ -75,6 +75,22 @@ static void virtio_gpu_free_object(struct drm_gem_object *obj)
> drm_gem_shmem_free_object(obj);
> }
>
> +static int virtio_gpu_gem_mmap(struct drm_gem_object *obj, struct vm_area_struct *vma)
> +{
> + pgprot_t prot;
> + int ret;
> +
> + ret = drm_gem_shmem_mmap(obj, vma);
> + if (ret < 0)
> + return ret;
> +
> + /* virtio-gpu needs normal caching, so clear writecombine */
> + prot = vm_get_page_prot(vma->vm_flags);
> + prot = pgprot_decrypted(prot);
> + vma->vm_page_prot = prot;
> + return 0;
> +}
> +
> static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .free = virtio_gpu_free_object,
> .open = virtio_gpu_gem_object_open,
> @@ -86,7 +102,7 @@ static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .get_sg_table = drm_gem_shmem_get_sg_table,
> .vmap = drm_gem_shmem_vmap,
Do we need vmap/vmunap? It seems optionable and also uses non-cacheable memory?
> .vunmap = drm_gem_shmem_vunmap,
> - .mmap = &drm_gem_shmem_mmap,
> + .mmap = &virtio_gpu_gem_mmap,
Why the &virtio_gpu_gem_mmap? Shouldn't just virtio_gpu_gem_mmap work?
> };
>
> struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
> --
> 2.18.1
>
^ permalink raw reply [flat|nested] 5+ messages in thread* RE: [PATCH] drm/virtio: fix mmap page attributes
2019-12-10 8:57 [PATCH] drm/virtio: fix mmap page attributes Gerd Hoffmann
2019-12-10 9:27 ` Thomas Zimmermann
2019-12-11 1:06 ` Gurchetan Singh
@ 2019-12-12 14:49 ` Ruhl, Michael J
2 siblings, 0 replies; 5+ messages in thread
From: Ruhl, Michael J @ 2019-12-12 14:49 UTC (permalink / raw)
To: Gerd Hoffmann, dri-devel
Cc: David Airlie, open list, open list:VIRTIO GPU DRIVER, gurchetansingh
>-----Original Message-----
>From: dri-devel <dri-devel-bounces@lists.freedesktop.org> On Behalf Of
>Gerd Hoffmann
>Sent: Tuesday, December 10, 2019 3:58 AM
>To: dri-devel@lists.freedesktop.org
>Cc: David Airlie <airlied@linux.ie>; open list <linux-kernel@vger.kernel.org>;
>open list:VIRTIO GPU DRIVER <virtualization@lists.linux-foundation.org>;
>Gerd Hoffmann <kraxel@redhat.com>; gurchetansingh@chromium.org
>Subject: [PATCH] drm/virtio: fix mmap page attributes
>
>virtio-gpu uses cached mappings. shmem helpers use writecombine though.
>So roll our own mmap function, wrapping drm_gem_shmem_mmap(), to
>tweak
>vm_page_prot accordingly.
>
>Reported-by: Gurchetan Singh <gurchetansingh@chromium.org>
>Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>---
> drivers/gpu/drm/virtio/virtgpu_object.c | 18 +++++++++++++++++-
> 1 file changed, 17 insertions(+), 1 deletion(-)
>
>diff --git a/drivers/gpu/drm/virtio/virtgpu_object.c
>b/drivers/gpu/drm/virtio/virtgpu_object.c
>index 017a9e0fc3bb..158610902054 100644
>--- a/drivers/gpu/drm/virtio/virtgpu_object.c
>+++ b/drivers/gpu/drm/virtio/virtgpu_object.c
>@@ -75,6 +75,22 @@ static void virtio_gpu_free_object(struct
>drm_gem_object *obj)
> drm_gem_shmem_free_object(obj);
> }
>
>+static int virtio_gpu_gem_mmap(struct drm_gem_object *obj, struct
>vm_area_struct *vma)
>+{
>+ pgprot_t prot;
>+ int ret;
>+
>+ ret = drm_gem_shmem_mmap(obj, vma);
>+ if (ret < 0)
>+ return ret;
>+
>+ /* virtio-gpu needs normal caching, so clear writecombine */
A minor nit.
I was looking at this code, trying to see where you were clearing the
writecombine bit.
Maybe a more clear comment would be:
virtio-gpu needs normal caching, re-do protection without writecombine
?
Mike
>+ prot = vm_get_page_prot(vma->vm_flags);
>+ prot = pgprot_decrypted(prot);
>+ vma->vm_page_prot = prot;
>+ return 0;
>+}
>+
> static const struct drm_gem_object_funcs virtio_gpu_gem_funcs = {
> .free = virtio_gpu_free_object,
> .open = virtio_gpu_gem_object_open,
>@@ -86,7 +102,7 @@ static const struct drm_gem_object_funcs
>virtio_gpu_gem_funcs = {
> .get_sg_table = drm_gem_shmem_get_sg_table,
> .vmap = drm_gem_shmem_vmap,
> .vunmap = drm_gem_shmem_vunmap,
>- .mmap = &drm_gem_shmem_mmap,
>+ .mmap = &virtio_gpu_gem_mmap,
> };
>
> struct drm_gem_object *virtio_gpu_create_object(struct drm_device *dev,
>--
>2.18.1
>
>_______________________________________________
>dri-devel mailing list
>dri-devel@lists.freedesktop.org
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^ permalink raw reply [flat|nested] 5+ messages in thread