mm/hmm: remove HMM_FAULT_SNAPSHOT

Now that flags are handled on a fine-grained per-page basis this global
flag is redundant and has a confusing overlap with the pfn_flags_mask and
default_flags.

Normalize the HMM_FAULT_SNAPSHOT behavior into one place. Callers needing
the SNAPSHOT behavior should set a pfn_flags_mask and default_flags that
always results in a cleared HMM_PFN_VALID. Then no pages will be faulted,
and HMM_FAULT_SNAPSHOT is not a special flow that overrides the masking
mechanism.

As this is the last flag, also remove the flags argument. If future flags
are needed they can be part of the struct hmm_range function arguments.

Link: https://lore.kernel.org/r/20200327200021.29372-5-jgg@ziepe.ca
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 95fec5968362621081136b4d43fa4f57f1f10d6d..4e3e9362afeb10e642e732dea04f1850da9069fa 100644 (file)
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -161,13 +161,11 @@ 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, unsigned int flags);
+  long hmm_range_fault(struct hmm_range *range);
 
-With the HMM_RANGE_SNAPSHOT flag, it will only fetch present CPU page table
-entries and will not trigger a page fault on missing or non-present entries.
-Without that flag, it does 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 like a CPU page fault.
+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
+like a CPU page fault.
 
 Both functions copy CPU page table entries into their pfns array argument. Each
 entry in that array corresponds to an address in the virtual range. HMM
@@ -197,7 +195,7 @@ The usage pattern is::
  again:
       range.notifier_seq = mmu_interval_read_begin(&interval_sub);
       down_read(&mm->mmap_sem);
-      ret = hmm_range_fault(&range, HMM_RANGE_SNAPSHOT);
+      ret = hmm_range_fault(&range);
       if (ret) {
           up_read(&mm->mmap_sem);
           if (ret == -EBUSY)

diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
index 90821ce5e6cad077b5af2e8a7ca9b7f2345abca0..c520290709371b58a5337b49381ed9a18178148e 100644 (file)
--- a/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_ttm.c
@@ -856,7 +856,7 @@ retry:
        range->notifier_seq = mmu_interval_read_begin(&bo->notifier);
 
        down_read(&mm->mmap_sem);
-       r = hmm_range_fault(range, 0);
+       r = hmm_range_fault(range);
        up_read(&mm->mmap_sem);
        if (unlikely(r <= 0)) {
                /*

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index 39c731a99937c65dd8d2e6a0640beffc42e7b2fc..e3797b2d4d17596ecd7a1906ce643c7a9de3dc24 100644 (file)
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -540,7 +540,7 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
                range.default_flags = 0;
                range.pfn_flags_mask = -1UL;
                down_read(&mm->mmap_sem);
-               ret = hmm_range_fault(&range, 0);
+               ret = hmm_range_fault(&range);
                up_read(&mm->mmap_sem);
                if (ret <= 0) {
                        if (ret == 0 || ret == -EBUSY)

diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index daee6508a3f60901b8c77c3c73ed7f56c4ac2e35..7475051100c7825675f499ad5ac93a8706a3f633 100644 (file)
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -117,13 +117,10 @@ static inline struct page *hmm_device_entry_to_page(const struct hmm_range *rang
        return pfn_to_page(entry >> range->pfn_shift);
 }
 
-/* Don't fault in missing PTEs, just snapshot the current state. */
-#define HMM_FAULT_SNAPSHOT             (1 << 1)
-
 /*
  * Please see Documentation/vm/hmm.rst for how to use the range API.
  */
-long hmm_range_fault(struct hmm_range *range, unsigned int flags);
+long hmm_range_fault(struct hmm_range *range);
 
 /*
  * HMM_RANGE_DEFAULT_TIMEOUT - default timeout (ms) when waiting for a range

diff --git a/mm/hmm.c b/mm/hmm.c
index 136de474221d77447f779a80ce61021feb42515e..8dbd9e1d0308b4d0bc2e92ca1c6836045b84e9e8 100644 (file)
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -29,7 +29,6 @@
 struct hmm_vma_walk {
        struct hmm_range        *range;
        unsigned long           last;
-       unsigned int            flags;
 };
 
 enum {
@@ -112,9 +111,6 @@ static unsigned int hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
 {
        struct hmm_range *range = hmm_vma_walk->range;
 
-       if (hmm_vma_walk->flags & HMM_FAULT_SNAPSHOT)
-               return 0;
-
        /*
         * So we not only consider the individual per page request we also
         * consider the default flags requested for the range. The API can
@@ -147,10 +143,17 @@ hmm_range_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
                     const uint64_t *pfns, unsigned long npages,
                     uint64_t cpu_flags)
 {
+       struct hmm_range *range = hmm_vma_walk->range;
        unsigned int required_fault = 0;
        unsigned long i;
 
-       if (hmm_vma_walk->flags & HMM_FAULT_SNAPSHOT)
+       /*
+        * If the default flags do not request to fault pages, and the mask does
+        * not allow for individual pages to be faulted, then
+        * hmm_pte_need_fault() will always return 0.
+        */
+       if (!((range->default_flags | range->pfn_flags_mask) &
+             range->flags[HMM_PFN_VALID]))
                return 0;
 
        for (i = 0; i < npages; ++i) {
@@ -557,7 +560,6 @@ static const struct mm_walk_ops hmm_walk_ops = {
 /**
  * hmm_range_fault - try to fault some address in a virtual address range
  * @range:     argument structure
- * @flags:     HMM_FAULT_* flags
  *
  * Return: the number of valid pages in range->pfns[] (from range start
  * address), which may be zero.  On error one of the following status codes
@@ -579,12 +581,11 @@ static const struct mm_walk_ops hmm_walk_ops = {
  * On error, for one virtual address in the range, the function will mark the
  * corresponding HMM pfn entry with an error flag.
  */
-long hmm_range_fault(struct hmm_range *range, unsigned int flags)
+long hmm_range_fault(struct hmm_range *range)
 {
        struct hmm_vma_walk hmm_vma_walk = {
                .range = range,
                .last = range->start,
-               .flags = flags,
        };
        struct mm_struct *mm = range->notifier->mm;
        int ret;