Re: [PATCH v3 2/6] drm/i915: Add support for asynchronous moving fence waiting

[Matthew Auld <matthew.auld@xxxxxxxxx>]

On 15/11/2021 12:42, Thomas Hellström wrote:
> On 11/15/21 13:36, Matthew Auld wrote:
> > On 14/11/2021 11:12, Thomas Hellström wrote:
> > > From: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> > >
> > > For now, we will only allow async migration when TTM is used,
> > > so the paths we care about are related to TTM.
> > >
> > > The mmap path is handled by having the fence in ttm_bo->moving,
> > > when pinning, the binding only becomes available after the moving
> > > fence is signaled, and pinning a cpu map will only work after
> > > the moving fence signals.
> > >
> > > This should close all holes where userspace can read a buffer
> > > before it's fully migrated.
> > >
> > > v2:
> > > - Fix a couple of SPARSE warnings
> > > v3:
> > > - Fix a NULL pointer dereference
> > >
> > > Co-developed-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Thomas Hellström <thomas.hellstrom@xxxxxxxxxxxxxxx>
> > > Signed-off-by: Maarten Lankhorst <maarten.lankhorst@xxxxxxxxxxxxxxx>
> > > ---
> > >   drivers/gpu/drm/i915/display/intel_fbdev.c    |  7 ++--
> > >   drivers/gpu/drm/i915/display/intel_overlay.c  |  2 +-
> > >   drivers/gpu/drm/i915/gem/i915_gem_pages.c     |  6 +++
> > >   .../i915/gem/selftests/i915_gem_coherency.c   |  4 +-
> > >   .../drm/i915/gem/selftests/i915_gem_mman.c    | 22 ++++++-----
> > >   drivers/gpu/drm/i915/i915_vma.c               | 39 ++++++++++++++++++-
> > >   drivers/gpu/drm/i915/i915_vma.h               |  3 ++
> > >   drivers/gpu/drm/i915/selftests/i915_vma.c     |  4 +-
> > >   8 files changed, 69 insertions(+), 18 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c 
> > > b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > > index adc3a81be9f7..5902ad0c2bd8 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_fbdev.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c
> > > @@ -265,11 +265,12 @@ static int intelfb_create(struct drm_fb_helper 
> > > *helper,
> > >           info->fix.smem_len = vma->node.size;
> > >       }
> > >   -    vaddr = i915_vma_pin_iomap(vma);
> > > +    vaddr = i915_vma_pin_iomap_unlocked(vma);
> > >       if (IS_ERR(vaddr)) {
> > > -        drm_err(&dev_priv->drm,
> > > -            "Failed to remap framebuffer into virtual memory\n");
> > >           ret = PTR_ERR(vaddr);
> > > +        if (ret != -EINTR && ret != -ERESTARTSYS)
> > > +            drm_err(&dev_priv->drm,
> > > +                "Failed to remap framebuffer into virtual memory\n");
> > >           goto out_unpin;
> > >       }
> > >       info->screen_base = vaddr;
> > > diff --git a/drivers/gpu/drm/i915/display/intel_overlay.c 
> > > b/drivers/gpu/drm/i915/display/intel_overlay.c
> > > index 7e3f5c6ca484..21593f3f2664 100644
> > > --- a/drivers/gpu/drm/i915/display/intel_overlay.c
> > > +++ b/drivers/gpu/drm/i915/display/intel_overlay.c
> > > @@ -1357,7 +1357,7 @@ static int get_registers(struct intel_overlay 
> > > *overlay, bool use_phys)
> > >           overlay->flip_addr = sg_dma_address(obj->mm.pages->sgl);
> > >       else
> > >           overlay->flip_addr = i915_ggtt_offset(vma);
> > > -    overlay->regs = i915_vma_pin_iomap(vma);
> > > +    overlay->regs = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >         if (IS_ERR(overlay->regs)) {
> > > diff --git a/drivers/gpu/drm/i915/gem/i915_gem_pages.c 
> > > b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > index c4f684b7cc51..49c6e55c68ce 100644
> > > --- a/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > +++ b/drivers/gpu/drm/i915/gem/i915_gem_pages.c
> > > @@ -418,6 +418,12 @@ void *i915_gem_object_pin_map(struct 
> > > drm_i915_gem_object *obj,
> > >       }
> > >         if (!ptr) {
> > > +        err = i915_gem_object_wait_moving_fence(obj, true);
> > > +        if (err) {
> > > +            ptr = ERR_PTR(err);
> > > +            goto err_unpin;
> > > +        }
> > > +
> > >           if (GEM_WARN_ON(type == I915_MAP_WC &&
> > >                   !static_cpu_has(X86_FEATURE_PAT)))
> > >               ptr = ERR_PTR(-ENODEV);
> > > diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c 
> > > b/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
> > > index 13b088cc787e..067c512961ba 100644
> > > --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
> > > +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_coherency.c
> > > @@ -101,7 +101,7 @@ static int gtt_set(struct context *ctx, unsigned 
> > > long offset, u32 v)
> > >         intel_gt_pm_get(vma->vm->gt);
> > >   -    map = i915_vma_pin_iomap(vma);
> > > +    map = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >       if (IS_ERR(map)) {
> > >           err = PTR_ERR(map);
> > > @@ -134,7 +134,7 @@ static int gtt_get(struct context *ctx, unsigned 
> > > long offset, u32 *v)
> > >         intel_gt_pm_get(vma->vm->gt);
> > >   -    map = i915_vma_pin_iomap(vma);
> > > +    map = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >       if (IS_ERR(map)) {
> > >           err = PTR_ERR(map);
> > > diff --git a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c 
> > > b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> > > index 6d30cdfa80f3..5d54181c2145 100644
> > > --- a/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> > > +++ b/drivers/gpu/drm/i915/gem/selftests/i915_gem_mman.c
> > > @@ -125,12 +125,13 @@ static int check_partial_mapping(struct 
> > > drm_i915_gem_object *obj,
> > >       n = page - view.partial.offset;
> > >       GEM_BUG_ON(n >= view.partial.size);
> > >   -    io = i915_vma_pin_iomap(vma);
> > > +    io = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >       if (IS_ERR(io)) {
> > > -        pr_err("Failed to iomap partial view: offset=%lu; err=%d\n",
> > > -               page, (int)PTR_ERR(io));
> > >           err = PTR_ERR(io);
> > > +        if (err != -EINTR && err != -ERESTARTSYS)
> > > +            pr_err("Failed to iomap partial view: offset=%lu; 
> > > err=%d\n",
> > > +                   page, err);
> > >           goto out;
> > >       }
> > >   @@ -219,12 +220,15 @@ static int check_partial_mappings(struct 
> > > drm_i915_gem_object *obj,
> > >           n = page - view.partial.offset;
> > >           GEM_BUG_ON(n >= view.partial.size);
> > >   -        io = i915_vma_pin_iomap(vma);
> > > +        io = i915_vma_pin_iomap_unlocked(vma);
> > >           i915_vma_unpin(vma);
> > >           if (IS_ERR(io)) {
> > > -            pr_err("Failed to iomap partial view: offset=%lu; 
> > > err=%d\n",
> > > -                   page, (int)PTR_ERR(io));
> > > -            return PTR_ERR(io);
> > > +            int err = PTR_ERR(io);
> > > +
> > > +            if (err != -EINTR && err != -ERESTARTSYS)
> > > +                pr_err("Failed to iomap partial view: offset=%lu; 
> > > err=%d\n",
> > > +                       page, err);
> > > +            return err;
> > >           }
> > >             iowrite32(page, io + n * PAGE_SIZE / sizeof(*io));
> > > @@ -773,7 +777,7 @@ static int gtt_set(struct drm_i915_gem_object *obj)
> > >           return PTR_ERR(vma);
> > >         intel_gt_pm_get(vma->vm->gt);
> > > -    map = i915_vma_pin_iomap(vma);
> > > +    map = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >       if (IS_ERR(map)) {
> > >           err = PTR_ERR(map);
> > > @@ -799,7 +803,7 @@ static int gtt_check(struct drm_i915_gem_object 
> > > *obj)
> > >           return PTR_ERR(vma);
> > >         intel_gt_pm_get(vma->vm->gt);
> > > -    map = i915_vma_pin_iomap(vma);
> > > +    map = i915_vma_pin_iomap_unlocked(vma);
> > >       i915_vma_unpin(vma);
> > >       if (IS_ERR(map)) {
> > >           err = PTR_ERR(map);
> > > diff --git a/drivers/gpu/drm/i915/i915_vma.c 
> > > b/drivers/gpu/drm/i915/i915_vma.c
> > > index 8781c4f61952..069f22b3cd48 100644
> > > --- a/drivers/gpu/drm/i915/i915_vma.c
> > > +++ b/drivers/gpu/drm/i915/i915_vma.c
> > > @@ -431,6 +431,13 @@ int i915_vma_bind(struct i915_vma *vma,
> > >               work->pinned = i915_gem_object_get(vma->obj);
> > >           }
> > >       } else {
> > > +        if (vma->obj) {
> > > +            int ret;
> > > +
> > > +            ret = i915_gem_object_wait_moving_fence(vma->obj, true);
> > > +            if (ret)
> > > +                return ret;
> > > +        }
> > >           vma->ops->bind_vma(vma->vm, NULL, vma, cache_level, 
> > > bind_flags);
> > >       }
> > >   @@ -455,6 +462,10 @@ void __iomem *i915_vma_pin_iomap(struct 
> > > i915_vma *vma)
> > >         ptr = READ_ONCE(vma->iomap);
> > >       if (ptr == NULL) {
> > > +        err = i915_gem_object_wait_moving_fence(vma->obj, true);
> > > +        if (err)
> > > +            goto err;
> > > +
> > >           /*
> > >            * TODO: consider just using i915_gem_object_pin_map() for 
> > > lmem
> > >            * instead, which already supports mapping non-contiguous 
> > > chunks
> > > @@ -496,6 +507,25 @@ void __iomem *i915_vma_pin_iomap(struct i915_vma 
> > > *vma)
> > >       return IO_ERR_PTR(err);
> > >   }
> > >   +void __iomem *i915_vma_pin_iomap_unlocked(struct i915_vma *vma)
> > > +{
> > > +    struct i915_gem_ww_ctx ww;
> > > +    void __iomem *map;
> > > +    int err;
> > > +
> > > +    for_i915_gem_ww(&ww, err, true) {
> > > +        err = i915_gem_object_lock(vma->obj, &ww);
> > > +        if (err)
> > > +            continue;
> > > +
> > > +        map = i915_vma_pin_iomap(vma);
> > > +    }
> > > +    if (err)
> > > +        map = IO_ERR_PTR(err);
> > > +
> > > +    return map;
> > > +}
> >
> > What is the reason for this change? Is this strictly related to this 
> > series/commit?
>
> Yes, it's because pulling out the moving fence requires the dma_resv lock.

Ok, I was thinking that vma_pin_iomap is only ever called on an already 
bound GGTT vma, for which we do a syncronous wait_for_bind, but maybe 
that's not always true?

Reviewed-by: Matthew Auld <matthew.auld@xxxxxxxxx>

> /Thomas