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-rw-r--r--Documentation/vm/hmm.rst35
-rw-r--r--include/linux/hmm.h13
-rw-r--r--mm/hmm.c12
3 files changed, 60 insertions, 0 deletions
diff --git a/Documentation/vm/hmm.rst b/Documentation/vm/hmm.rst
index 945d5fb6d14a..ec1efa32af3c 100644
--- a/Documentation/vm/hmm.rst
+++ b/Documentation/vm/hmm.rst
@@ -276,6 +276,41 @@ report commands as executed is serialized (there is no point in doing this
concurrently).
+Leverage default_flags and pfn_flags_mask
+=========================================
+
+The hmm_range struct has 2 fields default_flags and pfn_flags_mask that allows
+to set fault or snapshot policy for a whole range instead of having to set them
+for each entries in the range.
+
+For instance if the device flags for device entries are:
+ VALID (1 << 63)
+ WRITE (1 << 62)
+
+Now let say that device driver wants to fault with at least read a range then
+it does set:
+ range->default_flags = (1 << 63)
+ range->pfn_flags_mask = 0;
+
+and calls hmm_range_fault() as described above. This will fill fault all page
+in the range with at least read permission.
+
+Now let say driver wants to do the same except for one page in the range for
+which its want to have write. Now driver set:
+ range->default_flags = (1 << 63);
+ range->pfn_flags_mask = (1 << 62);
+ range->pfns[index_of_write] = (1 << 62);
+
+With this HMM will fault in all page with at least read (ie valid) and for the
+address == range->start + (index_of_write << PAGE_SHIFT) it will fault with
+write permission ie if the CPU pte does not have write permission set then HMM
+will call handle_mm_fault().
+
+Note that HMM will populate the pfns array with write permission for any entry
+that have write permission within the CPU pte no matter what are the values set
+in default_flags or pfn_flags_mask.
+
+
Represent and manage device memory from core kernel point of view
=================================================================
diff --git a/include/linux/hmm.h b/include/linux/hmm.h
index ec4bfa91648f..dee2f8953b2e 100644
--- a/include/linux/hmm.h
+++ b/include/linux/hmm.h
@@ -165,6 +165,8 @@ enum hmm_pfn_value_e {
* @pfns: array of pfns (big enough for the range)
* @flags: pfn flags to match device driver page table
* @values: pfn value for some special case (none, special, error, ...)
+ * @default_flags: default flags for the range (write, read, ... see hmm doc)
+ * @pfn_flags_mask: allows to mask pfn flags so that only default_flags matter
* @pfn_shifts: pfn shift value (should be <= PAGE_SHIFT)
* @valid: pfns array did not change since it has been fill by an HMM function
*/
@@ -177,6 +179,8 @@ struct hmm_range {
uint64_t *pfns;
const uint64_t *flags;
const uint64_t *values;
+ uint64_t default_flags;
+ uint64_t pfn_flags_mask;
uint8_t pfn_shift;
bool valid;
};
@@ -448,6 +452,15 @@ static inline int hmm_vma_fault(struct hmm_range *range, bool block)
{
long ret;
+ /*
+ * With the old API the driver must set each individual entries with
+ * the requested flags (valid, write, ...). So here we set the mask to
+ * keep intact the entries provided by the driver and zero out the
+ * default_flags.
+ */
+ range->default_flags = 0;
+ range->pfn_flags_mask = -1UL;
+
ret = hmm_range_register(range, range->vma->vm_mm,
range->start, range->end);
if (ret)
diff --git a/mm/hmm.c b/mm/hmm.c
index 3e07f32b94f8..0e21d3594ab6 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -419,6 +419,18 @@ static inline void hmm_pte_need_fault(const struct hmm_vma_walk *hmm_vma_walk,
if (!hmm_vma_walk->fault)
return;
+ /*
+ * So we not only consider the individual per page request we also
+ * consider the default flags requested for the range. The API can
+ * be use in 2 fashions. The first one where the HMM user coalesce
+ * multiple page fault into one request and set flags per pfns for
+ * of those faults. The second one where the HMM user want to pre-
+ * fault a range with specific flags. For the latter one it is a
+ * waste to have the user pre-fill the pfn arrays with a default
+ * flags value.
+ */
+ pfns = (pfns & range->pfn_flags_mask) | range->default_flags;
+
/* We aren't ask to do anything ... */
if (!(pfns & range->flags[HMM_PFN_VALID]))
return;