On Wed, Apr 22, 2020 at 07:52:29AM +0200, Christoph Hellwig wrote:

On Tue, Apr 21, 2020 at 09:21:43PM -0300, Jason Gunthorpe wrote:

...

From: Jason Gunthorpe jgg@mellanox.com

hmm_vma_walk->last is supposed to be updated after every write to the pfns, so that it can be returned by hmm_range_fault(). However, this is not done consistently. Fortunately nothing checks the return code of hmm_range_fault() for anything other than error.

More importantly last must be set before returning -EBUSY as it is used to prevent reading an output pfn as an input flags when the loop restarts.

For clarity and simplicity make hmm_range_fault() return 0 or -ERRNO. Only set last when returning -EBUSY.

Signed-off-by: Jason Gunthorpe jgg@mellanox.com Documentation/vm/hmm.rst | 2 +- drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c | 4 ++-- drivers/gpu/drm/nouveau/nouveau_svm.c | 6 +++--- include/linux/hmm.h | 2 +- mm/hmm.c | 25 +++++++++---------------- 5 files changed, 16 insertions(+), 23 deletions(-)

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst index 4e3e9362afeb10..9924f2caa0184c 100644 +++ b/Documentation/vm/hmm.rst @@ -161,7 +161,7 @@ device must complete the update before the driver callback returns. When the device driver wants to populate a range of virtual addresses, it can use::

• long hmm_range_fault(struct hmm_range *range);

• int hmm_range_fault(struct hmm_range *range);

It will trigger a page fault on missing or read-only entries if write access is requested (see below). Page faults use the generic mm page fault code path just diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c index 6309ff72bd7876..efc1329a019127 100644 +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c @@ -852,12 +852,12 @@ int amdgpu_ttm_tt_get_user_pages(struct amdgpu_bo *bo, struct page **pages) down_read(&mm->mmap_sem); r = hmm_range_fault(range); up_read(&mm->mmap_sem);

• if (unlikely(r <= 0)) {

• if (unlikely(r)) { /*
  • FIXME: This timeout should encompass the retry from
  • mmu_interval_read_retry() as well.
  */

• if ((r == 0 || r == -EBUSY) && !time_after(jiffies, timeout))
  

• if ((r == -EBUSY) && !time_after(jiffies, timeout))
  

Please also kill the superflous inner braces here.

...

• • Return: 0 or -ERRNO with one of the following status codes:

Maybe say something like:

* Returns 0 on success or one of the following error codes:

Otherwise this looks good:

Got it, thanks

Jason