diff options
| -rw-r--r-- | Documentation/vm/hmm.rst | 35 | ||||
| -rw-r--r-- | include/linux/hmm.h | 13 | ||||
| -rw-r--r-- | mm/hmm.c | 12 |
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) @@ -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; |