[PATCH v7 20/24] powerpc: book3s64: convert to pin_user_pages() and put_user_page()

John Hubbard
2019-11-21T07:16:59Z

1. Convert from get_user_pages() to pin_user_pages().

2. As required by pin_user_pages(), release these pages via
put_user_page(). In this case, do so via put_user_pages_dirty_lock().

That has the side effect of calling set_page_dirty_lock(), instead
of set_page_dirty(). This is probably more accurate.

As Christoph Hellwig put it, "set_page_dirty() is only safe if we are
dealing with a file backed page where we have reference on the inode it
hangs off." [1]

3. Release each page in mem->hpages[] (instead of mem->hpas[]), because
that is the array that pin_longterm_pages() filled in. This is more
accurate and should be a little safer from a maintenance point of
view.

[1] https://lore.kernel.org/r/20190723153640.GB720@lst.de

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
---
arch/powerpc/mm/book3s64/iommu_api.c | 12 +++++-------
1 file changed, 5 insertions(+), 7 deletions(-)

diff --git a/arch/powerpc/mm/book3s64/iommu_api.c b/arch/powerpc/mm/book3s64/iommu_api.c
index 56cc84520577..196383e8e5a9 100644
--- a/arch/powerpc/mm/book3s64/iommu_api.c
+++ b/arch/powerpc/mm/book3s64/iommu_api.c
@@ -103,7 +103,7 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
for (entry = 0; entry < entries; entry += chunk) {
unsigned long n = min(entries - entry, chunk);

- ret = get_user_pages(ua + (entry << PAGE_SHIFT), n,
+ ret = pin_user_pages(ua + (entry << PAGE_SHIFT), n,
FOLL_WRITE | FOLL_LONGTERM,
mem->hpages + entry, NULL);
if (ret == n) {
@@ -167,9 +167,8 @@ static long mm_iommu_do_alloc(struct mm_struct *mm, unsigned long ua,
return 0;

free_exit:
- /* free the reference taken */
- for (i = 0; i < pinned; i++)
- put_page(mem->hpages[i]);
+ /* free the references taken */
+ put_user_pages(mem->hpages, pinned);

vfree(mem->hpas);
kfree(mem);
@@ -212,10 +211,9 @@ static void mm_iommu_unpin(struct mm_iommu_table_group_mem_t *mem)
if (!page)
continue;

- if (mem->hpas[i] & MM_IOMMU_TABLE_GROUP_PAGE_DIRTY)
- SetPageDirty(page);
+ put_user_pages_dirty_lock(&mem->hpages[i], 1,
+ MM_IOMMU_TABLE_GROUP_PAGE_DIRTY);

- put_page(page);
mem->hpas[i] = 0;
}
}
--
2.24.0