| Message ID | 20220526235040.678984-3-dmitry.osipenko@collabora.com |
|---|---|
| State | New |
| Headers | show |
| Series | Add generic memory shrinker to VirtIO-GPU and Panfrost DRM drivers | expand |
On 6/29/22 11:43, Thomas Hellström (Intel) wrote: > > On 6/29/22 10:22, Dmitry Osipenko wrote: >> On 6/29/22 09:40, Thomas Hellström (Intel) wrote: >>> On 5/27/22 01:50, Dmitry Osipenko wrote: >>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't >>>> handle imported dma-bufs properly, which results in mapping of >>>> something >>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a >>>> hard >>>> lockup when userspace writes to the memory mapping of a dma-buf that >>>> was >>>> imported into Tegra's DRM GEM. >>>> >>>> To fix this bug, move mapping of imported dma-bufs to >>>> drm_gem_mmap_obj(). >>>> Now mmaping of imported dma-bufs works properly for all DRM drivers. >>> Same comment about Fixes: as in patch 1, >>>> Cc: stable@vger.kernel.org >>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> >>>> --- >>>> drivers/gpu/drm/drm_gem.c | 3 +++ >>>> drivers/gpu/drm/drm_gem_shmem_helper.c | 9 --------- >>>> drivers/gpu/drm/tegra/gem.c | 4 ++++ >>>> 3 files changed, 7 insertions(+), 9 deletions(-) >>>> >>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c >>>> index 86d670c71286..7c0b025508e4 100644 >>>> --- a/drivers/gpu/drm/drm_gem.c >>>> +++ b/drivers/gpu/drm/drm_gem.c >>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, >>>> unsigned long obj_size, >>>> if (obj_size < vma->vm_end - vma->vm_start) >>>> return -EINVAL; >>>> + if (obj->import_attach) >>>> + return dma_buf_mmap(obj->dma_buf, vma, 0); >>> If we start enabling mmaping of imported dma-bufs on a majority of >>> drivers in this way, how do we ensure that user-space is not blindly >>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC >>> which is needed before and after cpu access of mmap'ed dma-bufs? >>> >>> I was under the impression (admittedly without looking) that the few >>> drivers that actually called into dma_buf_mmap() had some private >>> user-mode driver code in place that ensured this happened. >> Since it's a userspace who does the mapping, then it should be a >> responsibility of userspace to do all the necessary syncing. > > Sure, but nothing prohibits user-space to ignore the syncing thinking > "It works anyway", testing those drivers where the syncing is a NOP. And > when a driver that finally needs syncing is tested it's too late to fix > all broken user-space. > >> I'm not >> sure whether anyone in userspace really needs to map imported dma-bufs >> in practice. Nevertheless, this use-case is broken and should be fixed >> by either allowing to do the mapping or prohibiting it. >> > Then I'd vote for prohibiting it, at least for now. And for the future > moving forward we could perhaps revisit the dma-buf need for syncing, > requiring those drivers that actually need it to implement emulated > coherent memory which can be done not too inefficiently (vmwgfx being > one example). Alright, I'll change it to prohibit the mapping. This indeed should be a better option.
On 7/4/22 15:33, Christian König wrote: > Am 30.06.22 um 01:06 schrieb Dmitry Osipenko: >> On 6/29/22 11:43, Thomas Hellström (Intel) wrote: >>> On 6/29/22 10:22, Dmitry Osipenko wrote: >>>> On 6/29/22 09:40, Thomas Hellström (Intel) wrote: >>>>> On 5/27/22 01:50, Dmitry Osipenko wrote: >>>>>> Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't >>>>>> handle imported dma-bufs properly, which results in mapping of >>>>>> something >>>>>> else than the imported dma-buf. For example, on NVIDIA Tegra we get a >>>>>> hard >>>>>> lockup when userspace writes to the memory mapping of a dma-buf that >>>>>> was >>>>>> imported into Tegra's DRM GEM. >>>>>> >>>>>> To fix this bug, move mapping of imported dma-bufs to >>>>>> drm_gem_mmap_obj(). >>>>>> Now mmaping of imported dma-bufs works properly for all DRM drivers. >>>>> Same comment about Fixes: as in patch 1, >>>>>> Cc: stable@vger.kernel.org >>>>>> Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> >>>>>> --- >>>>>> drivers/gpu/drm/drm_gem.c | 3 +++ >>>>>> drivers/gpu/drm/drm_gem_shmem_helper.c | 9 --------- >>>>>> drivers/gpu/drm/tegra/gem.c | 4 ++++ >>>>>> 3 files changed, 7 insertions(+), 9 deletions(-) >>>>>> >>>>>> diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c >>>>>> index 86d670c71286..7c0b025508e4 100644 >>>>>> --- a/drivers/gpu/drm/drm_gem.c >>>>>> +++ b/drivers/gpu/drm/drm_gem.c >>>>>> @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object >>>>>> *obj, >>>>>> unsigned long obj_size, >>>>>> if (obj_size < vma->vm_end - vma->vm_start) >>>>>> return -EINVAL; >>>>>> + if (obj->import_attach) >>>>>> + return dma_buf_mmap(obj->dma_buf, vma, 0); >>>>> If we start enabling mmaping of imported dma-bufs on a majority of >>>>> drivers in this way, how do we ensure that user-space is not blindly >>>>> using the object mmap without calling the needed DMA_BUF_IOCTL_SYNC >>>>> which is needed before and after cpu access of mmap'ed dma-bufs? >>>>> >>>>> I was under the impression (admittedly without looking) that the few >>>>> drivers that actually called into dma_buf_mmap() had some private >>>>> user-mode driver code in place that ensured this happened. >>>> Since it's a userspace who does the mapping, then it should be a >>>> responsibility of userspace to do all the necessary syncing. >>> Sure, but nothing prohibits user-space to ignore the syncing thinking >>> "It works anyway", testing those drivers where the syncing is a NOP. And >>> when a driver that finally needs syncing is tested it's too late to fix >>> all broken user-space. >>> >>>> I'm not >>>> sure whether anyone in userspace really needs to map imported dma-bufs >>>> in practice. Nevertheless, this use-case is broken and should be fixed >>>> by either allowing to do the mapping or prohibiting it. >>>> >>> Then I'd vote for prohibiting it, at least for now. And for the future >>> moving forward we could perhaps revisit the dma-buf need for syncing, >>> requiring those drivers that actually need it to implement emulated >>> coherent memory which can be done not too inefficiently (vmwgfx being >>> one example). >> Alright, I'll change it to prohibit the mapping. This indeed should be a >> better option. > > Oh, yes please. But I would expect that some people start screaming. > > Over time I've got tons of TTM patches because people illegally tried to > mmap() imported DMA-bufs in their driver. > > Anyway this is probably the right thing to do and we can work on fixing > the fallout later on. I already sent out the patch [1] that prohibits the mapping. Would be great if you all could take a look and give a r-b, thanks in advance. [1] https://patchwork.freedesktop.org/patch/492148/
diff --git a/drivers/gpu/drm/drm_gem.c b/drivers/gpu/drm/drm_gem.c index 86d670c71286..7c0b025508e4 100644 --- a/drivers/gpu/drm/drm_gem.c +++ b/drivers/gpu/drm/drm_gem.c @@ -1038,6 +1038,9 @@ int drm_gem_mmap_obj(struct drm_gem_object *obj, unsigned long obj_size, if (obj_size < vma->vm_end - vma->vm_start) return -EINVAL; + if (obj->import_attach) + return dma_buf_mmap(obj->dma_buf, vma, 0); + /* Take a ref for this mapping of the object, so that the fault * handler can dereference the mmap offset's pointer to the object. * This reference is cleaned up by the corresponding vm_close diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 8ad0e02991ca..6190f5018986 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -609,17 +609,8 @@ EXPORT_SYMBOL_GPL(drm_gem_shmem_vm_ops); */ int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma) { - struct drm_gem_object *obj = &shmem->base; int ret; - if (obj->import_attach) { - /* Drop the reference drm_gem_mmap_obj() acquired.*/ - drm_gem_object_put(obj); - vma->vm_private_data = NULL; - - return dma_buf_mmap(obj->dma_buf, vma, 0); - } - ret = drm_gem_shmem_get_pages(shmem); if (ret) { drm_gem_vm_close(vma); diff --git a/drivers/gpu/drm/tegra/gem.c b/drivers/gpu/drm/tegra/gem.c index 7c7dd84e6db8..f92aa20d63bb 100644 --- a/drivers/gpu/drm/tegra/gem.c +++ b/drivers/gpu/drm/tegra/gem.c @@ -564,6 +564,10 @@ int __tegra_gem_mmap(struct drm_gem_object *gem, struct vm_area_struct *vma) { struct tegra_bo *bo = to_tegra_bo(gem); + /* imported dmu-buf is mapped by drm_gem_mmap_obj() */ + if (gem->import_attach) + return 0; + if (!bo->pages) { unsigned long vm_pgoff = vma->vm_pgoff; int err;
Drivers that use drm_gem_mmap() and drm_gem_mmap_obj() helpers don't handle imported dma-bufs properly, which results in mapping of something else than the imported dma-buf. For example, on NVIDIA Tegra we get a hard lockup when userspace writes to the memory mapping of a dma-buf that was imported into Tegra's DRM GEM. To fix this bug, move mapping of imported dma-bufs to drm_gem_mmap_obj(). Now mmaping of imported dma-bufs works properly for all DRM drivers. Cc: stable@vger.kernel.org Signed-off-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> --- drivers/gpu/drm/drm_gem.c | 3 +++ drivers/gpu/drm/drm_gem_shmem_helper.c | 9 --------- drivers/gpu/drm/tegra/gem.c | 4 ++++ 3 files changed, 7 insertions(+), 9 deletions(-)