[PATCH] fs/proc/task_mmu: do not warn on seeing non-migration pmd entry

[Dev Jain]

pagemap_pmd_range_thp() warns if a non-present PMD is not a migration
entry. This became false once device-private entries at the PMD level were
added.

One can hit the warning by patching hmm-tests.c with the following:

diff --git a/tools/testing/selftests/mm/hmm-tests.c 
b/tools/testing/selftests/mm/hmm-tests.c
index e1c8a679a4cf3..7f0a3384f3c5f 100644
--- a/tools/testing/selftests/mm/hmm-tests.c
+++ b/tools/testing/selftests/mm/hmm-tests.c
@@ -209,6 +209,37 @@ static int hmm_dmirror_cmd(int fd,
        return 0;
 }

+static int hmm_read_self_pagemap(void *addr, unsigned long npages,
+                                unsigned long page_size)
+{
+       const size_t entry_size = sizeof(uint64_t);
+       const off_t offset = ((uintptr_t)addr / page_size) * entry_size;
+       uint64_t *entries;
+       ssize_t nread;
+       int fd;
+
+       entries = malloc(npages * entry_size);
+       if (!entries)
+               return -ENOMEM;
+
+       fd = open("/proc/self/pagemap", O_RDONLY);
+       if (fd < 0) {
+               free(entries);
+               return -errno;
+       }
+
+       nread = pread(fd, entries, npages * entry_size, offset);
+       close(fd);
+       free(entries);
+
+       if (nread < 0)
+               return -errno;
+       if ((size_t)nread != npages * entry_size)
+               return -EIO;
+
+       return 0;
+}
+
 static void hmm_buffer_free(struct hmm_buffer *buffer)
 {
        if (buffer == NULL)
@@ -2314,6 +2345,10 @@ TEST_F(hmm, migrate_anon_huge_fault)
        ASSERT_EQ(ret, 0);
        ASSERT_EQ(buffer->cpages, npages);

+       /* Exercise pagemap on a PMD device-private entry. */
+       ret = hmm_read_self_pagemap(buffer->ptr, npages, self->page_size);
+       ASSERT_EQ(ret, 0);
+
        /* Check what the device read. */
        for (i = 0, ptr = buffer->mirror; i < size / sizeof(*ptr); ++i)
                ASSERT_EQ(ptr[i], i);


Therefore, remove the stale migration-only assertion.

Fixes: a30b48bf1b24 ("mm/migrate_device: implement THP migration of zone device 
pages")
Cc: sta...@vger.kernel.org
Signed-off-by: Dev Jain <dev.j...@arm.com>
---
Applies on mm-unstable (404fb4f38e8f).

 fs/proc/task_mmu.c | 1 -
 1 file changed, 1 deletion(-)

diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
index 1e3a15bf46f4e..58938e62154d9 100644
--- a/fs/proc/task_mmu.c
+++ b/fs/proc/task_mmu.c
@@ -2129,7 +2129,6 @@ static int pagemap_pmd_range_thp(pmd_t *pmdp, unsigned 
long addr,
                        flags |= PM_SOFT_DIRTY;
                if (pmd_swp_uffd_wp(pmd))
                        flags |= PM_UFFD_WP;
-               VM_WARN_ON_ONCE(!pmd_is_migration_entry(pmd));
                page = softleaf_to_page(entry);
        }
 
-- 
2.43.0