+ mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier.patch added to mm-unstable branch

+ mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier.patch added to mm-unstable branch

[Andrew Morton]

The patch titled
     Subject: mm/hmm: make CONFIG_HMM_MIRROR select CONFIG_MMU_NOTIFIER
has been added to the -mm mm-unstable branch.  Its filename is
     mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier.patch

This patch will later appear in the mm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Andrew Morton <akpm@linux-foundation.org>
Subject: mm/hmm: make CONFIG_HMM_MIRROR select CONFIG_MMU_NOTIFIER
Date: Mon Jul 27 05:31:14 PM PDT 2026

hmm doesn't currently build well with MMU_NOTIFIER=n:

With microblaze
https://download.01.org/0day-ci/archive/20260702/202607021433.DYT5fDqE-lkp@intel.com/config
(CONFIG_MMU_NOTIFIER=n):

mm/hmm.c: In function 'hmm_range_fault_unlocked_timeout':
mm/hmm.c:804:25: error: implicit declaration of function 'mmu_interval_read_begin'; did you mean 'mmu_interval_check_retry'? [-Wimplicit-function-declaration]
  804 |                         mmu_interval_read_begin(range->notifier);
      |                         ^~~~~~~~~~~~~~~~~~~~~~~
      |                         mmu_interval_check_retry

Quoting Stanislav:

:  Documentation/mm/hmm.rst explicitly states:
: 
:  "Address space mirroring's main objective is to allow duplication of a
:  range of CPU page table into a device page table; HMM helps keep both
:  synchronized.  A device driver that wants to mirror a process address
:  space must start with the registration of a mmu_interval_notifier"
: 
:  I think making CONFIG_HMM_MIRROR dependent on the CONFIG_MMU_NOTIFIER
:  is the right thing to do.

So select MMU_NOTIFIER if hmm.c is to be compiled.

Cc: David Hildenbrand <david@kernel.org>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Cc: Stanislav Kinsburskii <skinsburskii@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/Kconfig |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/Kconfig~mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier
+++ a/mm/Kconfig
@@ -1250,6 +1250,7 @@ config ZONE_DEVICE
 config HMM_MIRROR
 	bool
 	depends on MMU
+	select MMU_NOTIFIER
 
 config GET_FREE_REGION
 	bool
_

Patches currently in -mm which might be from akpm@linux-foundation.org are

mm-mincore-use-walk_page_range_vma-in-do_mincore-fix.patch
csky-implement-flush_cache_vmap-in-c.patch
mm-annotate-data-race-in-cpu_needs_drain-fix.patch
mm-zsmalloc-encode-class-index-in-obj-value-for-lockless-class-lookup-fix.patch
mm-zsmalloc-drop-pool-lock-from-zs_free-on-64-bit-systems-fix.patch
mm-zsmalloc-drop-pool-lock-from-zs_free-on-64-bit-systems-fix-fix.patch
mm-rmap-use-huge_ptep_get-in-try_to_migrate_one-checkpatch-fixes.patch
mm-mprotect-use-huge_ptep_get-for-hugetlb-fix.patch
mm-drop-stale-folio_ref_count==1-check-in-do_swap_page-reuse-logic-fix.patch
alloc_tag-add-ioctl-to-proc-allocinfo-fix.patch
mm-hmm-make-config_hmm_mirror-select-config_mmu_notifier.patch
mm-vma-add-and-use-vma__pgoff-fix.patch
drivers-media-v4l2-core-v4l2-vp9c-reduce-inlining.patch