[PATCH v4 01/14] drm/ttm: Remap all page faults to per process dummy page.
Daniel Vetter
daniel at ffwll.ch
Tue Feb 2 14:21:58 UTC 2021
On Wed, Jan 27, 2021 at 09:29:41AM -0500, Andrey Grodzovsky wrote:
> Hey Daniel, just a ping.
Was on vacations last week.
> Andrey
>
> On 1/25/21 10:28 AM, Andrey Grodzovsky wrote:
> >
> > On 1/19/21 8:56 AM, Daniel Vetter wrote:
> > > On Mon, Jan 18, 2021 at 04:01:10PM -0500, Andrey Grodzovsky wrote:
> > > > On device removal reroute all CPU mappings to dummy page.
> > > >
> > > > v3:
> > > > Remove loop to find DRM file and instead access it
> > > > by vma->vm_file->private_data. Move dummy page installation
> > > > into a separate function.
> > > >
> > > > v4:
> > > > Map the entire BOs VA space into on demand allocated dummy page
> > > > on the first fault for that BO.
> > > >
> > > > Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky at amd.com>
> > > > ---
> > > > drivers/gpu/drm/ttm/ttm_bo_vm.c | 82
> > > > ++++++++++++++++++++++++++++++++++++++++-
> > > > include/drm/ttm/ttm_bo_api.h | 2 +
> > > > 2 files changed, 83 insertions(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > index 6dc96cf..ed89da3 100644
> > > > --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> > > > @@ -34,6 +34,8 @@
> > > > #include <drm/ttm/ttm_bo_driver.h>
> > > > #include <drm/ttm/ttm_placement.h>
> > > > #include <drm/drm_vma_manager.h>
> > > > +#include <drm/drm_drv.h>
> > > > +#include <drm/drm_managed.h>
> > > > #include <linux/mm.h>
> > > > #include <linux/pfn_t.h>
> > > > #include <linux/rbtree.h>
> > > > @@ -380,25 +382,103 @@ vm_fault_t
> > > > ttm_bo_vm_fault_reserved(struct vm_fault *vmf,
> > > > }
> > > > EXPORT_SYMBOL(ttm_bo_vm_fault_reserved);
> > > > +static void ttm_bo_release_dummy_page(struct drm_device *dev, void *res)
> > > > +{
> > > > + struct page *dummy_page = (struct page *)res;
> > > > +
> > > > + __free_page(dummy_page);
> > > > +}
> > > > +
> > > > +vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot)
> > > > +{
> > > > + struct vm_area_struct *vma = vmf->vma;
> > > > + struct ttm_buffer_object *bo = vma->vm_private_data;
> > > > + struct ttm_bo_device *bdev = bo->bdev;
> > > > + struct drm_device *ddev = bo->base.dev;
> > > > + vm_fault_t ret = VM_FAULT_NOPAGE;
> > > > + unsigned long address = vma->vm_start;
> > > > + unsigned long num_prefault = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
> > > > + unsigned long pfn;
> > > > + struct page *page;
> > > > + int i;
> > > > +
> > > > + /*
> > > > + * Wait for buffer data in transit, due to a pipelined
> > > > + * move.
> > > > + */
> > > > + ret = ttm_bo_vm_fault_idle(bo, vmf);
> > > > + if (unlikely(ret != 0))
> > > > + return ret;
> > > > +
> > > > + /* Allocate new dummy page to map all the VA range in this VMA to it*/
> > > > + page = alloc_page(GFP_KERNEL | __GFP_ZERO);
> > > > + if (!page)
> > > > + return VM_FAULT_OOM;
> > > > +
> > > > + pfn = page_to_pfn(page);
> > > > +
> > > > + /*
> > > > + * Prefault the entire VMA range right away to avoid further faults
> > > > + */
> > > > + for (i = 0; i < num_prefault; ++i) {
> > > > +
> > > > + if (unlikely(address >= vma->vm_end))
> > > > + break;
> > > > +
> > > > + if (vma->vm_flags & VM_MIXEDMAP)
> > > > + ret = vmf_insert_mixed_prot(vma, address,
> > > > + __pfn_to_pfn_t(pfn, PFN_DEV),
> > > > + prot);
> > > > + else
> > > > + ret = vmf_insert_pfn_prot(vma, address, pfn, prot);
> > > > +
> > > > + /* Never error on prefaulted PTEs */
> > > > + if (unlikely((ret & VM_FAULT_ERROR))) {
> > > > + if (i == 0)
> > > > + return VM_FAULT_NOPAGE;
> > > > + else
> > > > + break;
> > > > + }
> > > > +
> > > > + address += PAGE_SIZE;
> > > > + }
> > > > +
> > > > + /* Set the page to be freed using drmm release action */
> > > > + if (drmm_add_action_or_reset(ddev, ttm_bo_release_dummy_page, page))
> > > > + return VM_FAULT_OOM;
> > > > +
> > > > + return ret;
> > > > +}
> > > > +EXPORT_SYMBOL(ttm_bo_vm_dummy_page);
> > > I think we can lift this entire thing (once the ttm_bo_vm_fault_idle is
> > > gone) to the drm level, since nothing ttm specific in here. Probably stuff
> > > it into drm_gem.c (but really it's not even gem specific, it's fully
> > > generic "replace this vma with dummy pages pls" function.
> >
> >
> > Once I started with this I noticed that drmm_add_action_or_reset depends
> > on struct drm_device *ddev = bo->base.dev and bo is the private data
> > we embed at the TTM level when setting up the mapping and so this forces
> > to move drmm_add_action_or_reset out of this function to every client who uses
> > this function, and then you separate the logic of page allocation from
> > it's release.
> > So I suggest we keep it as is.
Uh disappointing. Thing is, ttm essentially means drm devices with gem, except for
vmwgfx, which is a drm_device without gem. And I think one of the
remaining ttm refactors in this area is to move ttm_device over into
drm_device someone, and then we'd have bo->base.dev always set to
something that drmm_add_action_or_reset can use.
I guess hand-rolling for now and jotting this down as a TODO item is fine
too, but would be good to get this addressed since that's another reason
here to do this. Maybe sync with Christian how to best do this.
-Daniel
> >
> > Andrey
> >
> >
> > >
> > > Aside from this nit I think the overall approach you have here is starting
> > > to look good. Lots of work&polish, but imo we're getting there and can
> > > start landing stuff soon.
> > > -Daniel
> > >
> > > > +
> > > > vm_fault_t ttm_bo_vm_fault(struct vm_fault *vmf)
> > > > {
> > > > struct vm_area_struct *vma = vmf->vma;
> > > > pgprot_t prot;
> > > > struct ttm_buffer_object *bo = vma->vm_private_data;
> > > > + struct drm_device *ddev = bo->base.dev;
> > > > vm_fault_t ret;
> > > > + int idx;
> > > > ret = ttm_bo_vm_reserve(bo, vmf);
> > > > if (ret)
> > > > return ret;
> > > > prot = vma->vm_page_prot;
> > > > - ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
> > > > + if (drm_dev_enter(ddev, &idx)) {
> > > > + ret = ttm_bo_vm_fault_reserved(vmf, prot, TTM_BO_VM_NUM_PREFAULT, 1);
> > > > + drm_dev_exit(idx);
> > > > + } else {
> > > > + ret = ttm_bo_vm_dummy_page(vmf, prot);
> > > > + }
> > > > if (ret == VM_FAULT_RETRY && !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT))
> > > > return ret;
> > > > dma_resv_unlock(bo->base.resv);
> > > > return ret;
> > > > +
> > > > + return ret;
> > > > }
> > > > EXPORT_SYMBOL(ttm_bo_vm_fault);
> > > > diff --git a/include/drm/ttm/ttm_bo_api.h b/include/drm/ttm/ttm_bo_api.h
> > > > index e17be32..12fb240 100644
> > > > --- a/include/drm/ttm/ttm_bo_api.h
> > > > +++ b/include/drm/ttm/ttm_bo_api.h
> > > > @@ -643,4 +643,6 @@ void ttm_bo_vm_close(struct vm_area_struct *vma);
> > > > int ttm_bo_vm_access(struct vm_area_struct *vma, unsigned long addr,
> > > > void *buf, int len, int write);
> > > > +vm_fault_t ttm_bo_vm_dummy_page(struct vm_fault *vmf, pgprot_t prot);
> > > > +
> > > > #endif
> > > > --
> > > > 2.7.4
> > > >
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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