[PATCH mm-unstable v1 11/20] RDMA/usnic: remove FOLL_FORCE usage

David Hildenbrand
2022-11-16T10:38:59Z

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: Christian Benvenuti <benve@cisco.com>
Cc: Nelson Escobar <neescoba@cisco.com>
Cc: Jason Gunthorpe <jgg@ziepe.ca>
Cc: Leon Romanovsky <leon@kernel.org>
Signed-off-by: David Hildenbrand <david@redhat.com>
---
drivers/infiniband/hw/usnic/usnic_uiom.c | 9 ++++-----
1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/infiniband/hw/usnic/usnic_uiom.c b/drivers/infiniband/hw/usnic/usnic_uiom.c
index 67923ced6e2d..c301b3be9f30 100644
--- a/drivers/infiniband/hw/usnic/usnic_uiom.c
+++ b/drivers/infiniband/hw/usnic/usnic_uiom.c
@@ -85,6 +85,7 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
int dmasync, struct usnic_uiom_reg *uiomr)
{
struct list_head *chunk_list = &uiomr->chunk_list;
+ unsigned int gup_flags = FOLL_LONGTERM;
struct page **page_list;
struct scatterlist *sg;
struct usnic_uiom_chunk *chunk;
@@ -96,7 +97,6 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
int off;
int i;
dma_addr_t pa;
- unsigned int gup_flags;
struct mm_struct *mm;

/*
@@ -131,8 +131,8 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
goto out;
}

- gup_flags = FOLL_WRITE;
- gup_flags |= (writable) ? 0 : FOLL_FORCE;
+ if (writable)
+ gup_flags |= FOLL_WRITE;
cur_base = addr & PAGE_MASK;
ret = 0;

@@ -140,8 +140,7 @@ static int usnic_uiom_get_pages(unsigned long addr, size_t size, int writable,
ret = pin_user_pages(cur_base,
min_t(unsigned long, npages,
PAGE_SIZE / sizeof(struct page *)),
- gup_flags | FOLL_LONGTERM,
- page_list, NULL);
+ gup_flags, page_list, NULL);

if (ret < 0)
goto out;
--
2.38.1