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Subject[PATCH 07/22] mm/hmm: Use hmm_mirror not mm as an argument for hmm_range_register
Date
From: Jason Gunthorpe <jgg@mellanox.com>

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@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Tested-by: Philip Yang <Philip.Yang@amd.com>
---
drivers/gpu/drm/nouveau/nouveau_svm.c | 2 +-
include/linux/hmm.h | 7 ++++---
mm/hmm.c | 13 ++++---------
3 files changed, 9 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 93ed43c413f0..8c92374afcf2 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 cb01cf1fa3c0..1fba6979adf4 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -496,7 +496,7 @@ 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);
@@ -532,7 +532,8 @@ 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;

@@ -545,7 +546,7 @@ 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 f6956d78e3cb..22a97ada108b 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -914,13 +914,13 @@ 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;
@@ -934,20 +934,15 @@ 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;
- }

/* Initialize range to track CPU page table updates. */
mutex_lock(&hmm->lock);

range->hmm = hmm;
+ kref_get(&hmm->kref);
list_add_rcu(&range->list, &hmm->ranges);

/*
--
2.20.1
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