From 023a019a9b4e90b9df8ed5be591787b5c914d74f Mon Sep 17 00:00:00 2001 From: Jérôme Glisse Date: Mon, 13 May 2019 17:20:05 -0700 Subject: mm/hmm: add default fault flags to avoid the need to pre-fill pfns arrays MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Reviewed-by: Ralph Campbell Cc: John Hubbard Cc: Dan Williams Cc: Arnd Bergmann Cc: Balbir Singh Cc: Dan Carpenter Cc: Ira Weiny Cc: Matthew Wilcox Cc: Souptick Joarder Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- Documentation/vm/hmm.rst | 35 +++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) (limited to 'Documentation/vm') 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 ================================================================= -- cgit v1.2.3