Re: [Xen-devel] [PATCH v2 14/15] drm/amdgpu: Use mmu_range_notifier instead of hmm_mirror

["Yang, Philip" <Philip.Yang@xxxxxxx>]

Sorry, resend patch, the one in previous email missed couple of lines 
duo to copy/paste.

On 2019-11-01 3:45 p.m., Yang, Philip wrote:
> 
> 
> On 2019-11-01 1:42 p.m., Jason Gunthorpe wrote:
>> On Fri, Nov 01, 2019 at 03:59:26PM +0000, Yang, Philip wrote:
>>>> This test for range_blockable should be before mutex_lock, I can move
>>>> it up
>>>>
>>> yes, thanks.
>>
>> Okay, I wrote it like this:
>>
>>      if (mmu_notifier_range_blockable(range))
>>              mutex_lock(&adev->notifier_lock);
>>      else if (!mutex_trylock(&adev->notifier_lock))
>>              return false;
>>
>>>> Also, do you know if notifier_lock is held while calling
>>>> amdgpu_ttm_tt_get_user_pages_done()? Can we add a 'lock assert held'
>>>> to amdgpu_ttm_tt_get_user_pages_done()?
>>>
>>> gpu side hold notifier_lock but kfd side doesn't. kfd side doesn't check
>>> amdgpu_ttm_tt_get_user_pages_done/mmu_range_read_retry return value but
>>> check mem->invalid flag which is updated from invalidate callback. It
>>> takes more time to change, I will come to another patch to fix it later.
>>
>> Ah.. confusing, OK, I'll let you sort that
>>
>>>> However, this is all pre-existing bugs, so I'm OK go ahead with this
>>>> patch as modified. I advise AMD to make a followup patch ..
>>>>
>>> yes, I will.
>>
>> While you are here, this is also wrong:
>>
>> int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages)
>> {
>>      down_read(&mm->mmap_sem);
>>      r = hmm_range_fault(range, 0);
>>      up_read(&mm->mmap_sem);
>>      if (unlikely(r <= 0)) {
>>              if ((r == 0 || r == -EBUSY) && !time_after(jiffies, timeout))
>>                      goto retry;
>>              goto out_free_pfns;
>>      }
>>
>>      for (i = 0; i < ttm->num_pages; i++) {
>>              pages[i] = hmm_device_entry_to_page(range, range->pfns[i]);
>>
>> It is not allowed to read the results of hmm_range_fault() outside
>> locking, and in particular, we can't convert to a struct page.
>>
>> This must be done inside the notifier_lock, after checking
>> mmu_range_read_retry(), all handling of the struct page must be
>> structured like that.
>>
> Below change will fix this, then driver will call mmu_range_read_retry
> second time using same range->notifier_seq to check if range is
> invalidated inside amdgpu_cs_submit, this looks ok for me.
> 
@@ -797,6 +797,7 @@ static const uint64_t 
hmm_range_values[HMM_PFN_VALUE_MAX] = {
   */
  int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page 
**pages)
  {
+       struct amdgpu_device *adev = amdgpu_ttm_adev(bo->tbo.bdev);
         struct ttm_tt *ttm = bo->tbo.ttm;
         struct amdgpu_ttm_tt *gtt = (void *)ttm;
         unsigned long start = gtt->userptr;
@@ -868,6 +869,13 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo 
*bo, struct page **pages)
                 goto out_free_pfns;
         }

+       mutex_lock(&adev->notifier_lock);
+
+       if (mmu_range_read_retry(&bo->notifier, range->notifier_seq)) {
+               mutex_unlock(&adev->notifier_lock);
+               goto retry;
+       }
+
         for (i = 0; i < ttm->num_pages; i++) {
                 pages[i] = hmm_device_entry_to_page(range, range->pfns[i]);
                 if (unlikely(!pages[i])) {
@@ -875,10 +883,12 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo 
*bo, struct page **pages)
                                i, range->pfns[i]);
                         r = -ENOMEM;

+                       mutex_unlock(&adev->notifier_lock);
                         goto out_free_pfns;
                 }
         }

+       mutex_unlock(&adev->notifier_lock);
         gtt->range = range;
         mmput(mm);

> 
> Philip
> 
>>>>> @@ -997,10 +1004,18 @@ static void amdgpu_ttm_tt_unpin_userptr(struct 
>>>>> ttm_tt *ttm)
>>>>>           sg_free_table(ttm->sg);
>>>>>     
>>>>>     #if IS_ENABLED(CONFIG_DRM_AMDGPU_USERPTR)
>>>>> - if (gtt->range &&
>>>>> -     ttm->pages[0] == hmm_device_entry_to_page(gtt->range,
>>>>> -                                               gtt->range->pfns[0]))
>>>>> -         WARN_ONCE(1, "Missing get_user_page_done\n");
>>>>> + if (gtt->range) {
>>>>> +         unsigned long i;
>>>>> +
>>>>> +         for (i = 0; i < ttm->num_pages; i++) {
>>>>> +                 if (ttm->pages[i] !=
>>>>> +                         hmm_device_entry_to_page(gtt->range,
>>>>> +                                       gtt->range->pfns[i]))
>>>>> +                         break;
>>>>> +         }
>>>>> +
>>>>> +         WARN((i == ttm->num_pages), "Missing get_user_page_done\n");
>>>>> + }
>>>>
>>>> Is this related/necessary? I can put it in another patch if it is just
>>>> debugging improvement? Please advise
>>>>
>>> I see this WARN backtrace now, but I didn't see it before. This is
>>> somehow related.
>>
>> Hm, might be instructive to learn what is going on..
>>
>> Thanks,
>> Jason
>>
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