On Thu, Jun 06, 2019 at 03:44:29PM -0300, Jason Gunthorpe wrote:
> From: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
>
> Ralph observes that hmm_range_register() can only be called by a driver
> while a mirror is registered. Make this clear in the API by passing in the
> mirror structure as a parameter.
>
> This also simplifies understanding the lifetime model for struct hmm, as
> the hmm pointer must be valid as part of a registered mirror so all we
> need in hmm_register_range() is a simple kref_get.
>
> Suggested-by: Ralph Campbell <rcampbell@xxxxxxxxxx>
> Signed-off-by: Jason Gunthorpe <jgg@xxxxxxxxxxxx>
> ---
> v2
> - Include the oneline patch to nouveau_svm.c
> ---
> drivers/gpu/drm/nouveau/nouveau_svm.c | 2 +-
> include/linux/hmm.h | 7 ++++---
> mm/hmm.c | 15 ++++++---------
> 3 files changed, 11 insertions(+), 13 deletions(-)
>
> diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
> index 93ed43c413f0bb..8c92374afcf227 100644
> --- a/drivers/gpu/drm/nouveau/nouveau_svm.c
> +++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
> @@ -649,7 +649,7 @@ nouveau_svm_fault(struct nvif_notify *notify)
> range.values = nouveau_svm_pfn_values;
> range.pfn_shift = NVIF_VMM_PFNMAP_V0_ADDR_SHIFT;
> again:
> - ret = hmm_vma_fault(&range, true);
> + ret = hmm_vma_fault(&svmm->mirror, &range, true);
> if (ret == 0) {
> mutex_lock(&svmm->mutex);
> if (!hmm_vma_range_done(&range)) {
> diff --git a/include/linux/hmm.h b/include/linux/hmm.h
> index 688c5ca7068795..2d519797cb134a 100644
> --- a/include/linux/hmm.h
> +++ b/include/linux/hmm.h
> @@ -505,7 +505,7 @@ static inline bool hmm_mirror_mm_is_alive(struct hmm_mirror *mirror)
> * Please see Documentation/vm/hmm.rst for how to use the range API.
> */
> int hmm_range_register(struct hmm_range *range,
> - struct mm_struct *mm,
> + struct hmm_mirror *mirror,
> unsigned long start,
> unsigned long end,
> unsigned page_shift);
> @@ -541,7 +541,8 @@ static inline bool hmm_vma_range_done(struct hmm_range *range)
> }
>
> /* This is a temporary helper to avoid merge conflict between trees. */
> -static inline int hmm_vma_fault(struct hmm_range *range, bool block)
> +static inline int hmm_vma_fault(struct hmm_mirror *mirror,
> + struct hmm_range *range, bool block)
> {
> long ret;
>
> @@ -554,7 +555,7 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
> range->default_flags = 0;
> range->pfn_flags_mask = -1UL;
>
> - ret = hmm_range_register(range, range->vma->vm_mm,
> + ret = hmm_range_register(range, mirror,
> range->start, range->end,
> PAGE_SHIFT);
> if (ret)
> diff --git a/mm/hmm.c b/mm/hmm.c
> index 547002f56a163d..8796447299023c 100644
> --- a/mm/hmm.c
> +++ b/mm/hmm.c
> @@ -925,13 +925,13 @@ static void hmm_pfns_clear(struct hmm_range *range,
> * Track updates to the CPU page table see include/linux/hmm.h
> */
> int hmm_range_register(struct hmm_range *range,
> - struct mm_struct *mm,
> + struct hmm_mirror *mirror,
> unsigned long start,
> unsigned long end,
> unsigned page_shift)
> {
> unsigned long mask = ((1UL << page_shift) - 1UL);
> - struct hmm *hmm;
> + struct hmm *hmm = mirror->hmm;
>
> range->valid = false;
> range->hmm = NULL;
> @@ -945,15 +945,12 @@ int hmm_range_register(struct hmm_range *range,
> range->start = start;
> range->end = end;
>
> - hmm = hmm_get_or_create(mm);
> - if (!hmm)
> - return -EFAULT;
> -
> /* Check if hmm_mm_destroy() was call. */
> - if (hmm->mm == NULL || hmm->dead) {
> - hmm_put(hmm);
> + if (hmm->mm == NULL || hmm->dead)
> return -EFAULT;
> - }
> +
> + range->hmm = hmm;
I don't think you need this assignment here. In the code below (right after
the mutext_lock()) it is set already. And looks like it remains that way after
the end of the series.
Reviewed-by: Ira Weiny <ira.weiny@xxxxxxxxx>
> + kref_get(&hmm->kref);
>
> /* Initialize range to track CPU page table updates. */
> mutex_lock(&hmm->lock);
> --
> 2.21.0
>
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