[PATCH mm-unstable v1 12/20] RDMA/siw: remove FOLL_FORCE usage

David Hildenbrand
2022-11-16T10:26:51Z

GUP now supports reliable R/O long-term pinning in COW mappings, such
that we break COW early. MAP_SHARED VMAs only use the shared zeropage so
far in one corner case (DAXFS file with holes), which can be ignored
because GUP does not support long-term pinning in fsdax (see
check_vma_flags()).

Consequently, FOLL_FORCE | FOLL_WRITE | FOLL_LONGTERM is no longer required
for reliable R/O long-term pinning: FOLL_LONGTERM is sufficient. So stop
using FOLL_FORCE, which is really only for ptrace access.

Cc: Bernard Metzler <bmt@zurich.ibm.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
drivers/infiniband/sw/siw/siw_mem.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/sw/siw/siw_mem.c b/drivers/infiniband/sw/siw/siw_mem.c
index 61c17db70d65..b2b33dd3b4fa 100644
--- a/drivers/infiniband/sw/siw/siw_mem.c
+++ b/drivers/infiniband/sw/siw/siw_mem.c
@@ -368,7 +368,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
struct mm_struct *mm_s;
u64 first_page_va;
unsigned long mlock_limit;
- unsigned int foll_flags = FOLL_WRITE;
+ unsigned int foll_flags = FOLL_LONGTERM;
int num_pages, num_chunks, i, rv = 0;

if (!can_do_mlock())
@@ -391,8 +391,8 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)

mmgrab(mm_s);

- if (!writable)
- foll_flags |= FOLL_FORCE;
+ if (writable)
+ foll_flags |= FOLL_WRITE;

mmap_read_lock(mm_s);

@@ -423,8 +423,7 @@ struct siw_umem *siw_umem_get(u64 start, u64 len, bool writable)
while (nents) {
struct page **plist = &umem->page_chunk[i].plist[got];

- rv = pin_user_pages(first_page_va, nents,
- foll_flags | FOLL_LONGTERM,
+ rv = pin_user_pages(first_page_va, nents, foll_flags,
plist, NULL);
if (rv < 0)
goto out_sem_up;
--
2.38.1