mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays

The HMM mirror API can be use in two fashions.  The first one where the
HMM user coalesce multiple page faults 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.

This patch adds a default flags value allowing user to set them for a
range without having to pre-fill the pfn array.

Link: http://lkml.kernel.org/r/20190403193318.16478-8-jglisse@redhat.com
Signed-off-by: Jérôme Glisse <jglisse@redhat.com>
Reviewed-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: John Hubbard <jhubbard@nvidia.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Balbir Singh <bsingharora@gmail.com>
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Cc: Ira Weiny <ira.weiny@intel.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 13 insertions, 0 deletions

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)