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Merge tag 'for-linus-hmm' of git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma

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Pull hmm updates from Jason Gunthorpe:
 "This series adds a selftest for hmm_range_fault() and several of the
  DEVICE_PRIVATE migration related actions, and another simplification
  for hmm_range_fault()'s API.

   - Simplify hmm_range_fault() with a simpler return code, no
     HMM_PFN_SPECIAL, and no customizable output PFN format

   - Add a selftest for hmm_range_fault() and DEVICE_PRIVATE related
     functionality"

* tag 'for-linus-hmm' of git://git.kernel.org/pub/scm/linux/kernel/git/rdma/rdma:
  MAINTAINERS: add HMM selftests
  mm/hmm/test: add selftests for HMM
  mm/hmm/test: add selftest driver for HMM
  mm/hmm: remove the customizable pfn format from hmm_range_fault
  mm/hmm: remove HMM_PFN_SPECIAL
  drm/amdgpu: remove dead code after hmm_range_fault()
  mm/hmm: make hmm_range_fault return 0 or -1
This commit is contained in:
Linus Torvalds
2020-06-02 14:05:27 -07:00
parent 194098915a f07e2f6be3
commit cfa3b8068b
18 changed files with 2934 additions and 289 deletions
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30
Documentation/vm/hmm.rst
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@@ -161,7 +161,7 @@ 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);
int hmm_range_fault(struct hmm_range *range);
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
@@ -184,10 +184,7 @@ The usage pattern is::
range.notifier = &interval_sub;
range.start = ...;
range.end = ...;
range.pfns = ...;
range.flags = ...;
range.values = ...;
range.pfn_shift = ...;
range.hmm_pfns = ...;
if (!mmget_not_zero(interval_sub->notifier.mm))
return -EFAULT;
@@ -229,15 +226,10 @@ The hmm_range struct has 2 fields, default_flags and pfn_flags_mask, that specif
fault or snapshot policy for the whole range instead of having to set them
for each entry in the pfns array.
For instance, if the device flags for range.flags are::
For instance if the device driver wants pages for a range with at least read
permission, it sets::
range.flags[HMM_PFN_VALID] = (1 << 63);
range.flags[HMM_PFN_WRITE] = (1 << 62);
and the device driver wants pages for a range with at least read permission,
it sets::
range->default_flags = (1 << 63);
range->default_flags = HMM_PFN_REQ_FAULT;
range->pfn_flags_mask = 0;
and calls hmm_range_fault() as described above. This will fill fault all pages
@@ -246,18 +238,18 @@ in the range with at least read permission.
Now let's say the driver wants to do the same except for one page in the range for
which it wants to have write permission. Now driver set::
range->default_flags = (1 << 63);
range->pfn_flags_mask = (1 << 62);
range->pfns[index_of_write] = (1 << 62);
range->default_flags = HMM_PFN_REQ_FAULT;
range->pfn_flags_mask = HMM_PFN_REQ_WRITE;
range->pfns[index_of_write] = HMM_PFN_REQ_WRITE;
With this, HMM will fault in all pages with at least read (i.e., valid) and for the
address == range->start + (index_of_write << PAGE_SHIFT) it will fault with
write permission i.e., 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 page
that is mapped with CPU write permission no matter what values are set
in default_flags or pfn_flags_mask.
After hmm_range_fault completes the flag bits are set to the current state of
the page tables, ie HMM_PFN_VALID | HMM_PFN_WRITE will be set if the page is
writable.
Represent and manage device memory from core kernel point of view