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

[Matthew Auld <matthew.auld@intel.com>]

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@linux.intel.com>
>>>
>>> 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@linux.intel.com>
>>> Signed-off-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
>>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>>> ---
>>>   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@intel.com>

> 
> /Thomas
> 
>