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

["Thomas Hellström" <thomas.hellstrom@linux.intel.com>]

On 11/15/21 14:13, Matthew Auld wrote:
> 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?
>
Hmm, Good point. We should probably replace that vma_pin_iomap stuff 
with an assert that the
binding fence is indeed signaled and error free? Because if binding 
succeeded, no need to check the moving fence.

/Thomas



> Reviewed-by: Matthew Auld <matthew.auld@intel.com>
>
>>
>> /Thomas
>>
>>