On 2020-05-05 12:14, Souptick Joarder wrote:
Currently {get|pin}_user_pages_fast() have 3 return value 0, -errno
and no of pinned pages. The only case where these two functions will
return 0, is for nr_pages <= 0, which doesn't find a valid use case.
But if at all any, then a -ERRNO will be returned instead of 0, which
means {get|pin}_user_pages_fast() will have 2 return values -errno &
no of pinned pages.
Update all the callers which deals with return value 0 accordingly.
Hmmm, seems a little shaky. In order to do this safely, I'd recommend
first changing gup_fast/pup_fast so so that they return -EINVAL if
the caller specified nr_pages==0, and of course auditing all callers,
to ensure that this won't cause problems.
The gup.c documentation would also need updating in a couple of comment
blocks, above get_user_pages_remote(), and __get_user_pages(), because
those talk about a zero return value.
This might be practical without slowing down the existing code, because
there is already a check in place, so just tweaking it like this (untested)
won't change performance at all:
diff --git a/mm/gup.c b/mm/gup.c
index 11fda538c9d9..708eed79ae29 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2787,7 +2787,7 @@ static int internal_get_user_pages_fast(unsigned long start,
int nr_pages,
end = start + len;
if (end <= start)
- return 0;
+ return -EINVAL;
if (unlikely(!access_ok((void __user *)start, len)))
return -EFAULT;
...although I might be missing some other things that need a similar change,
so you should look carefully for yourself.
Once that change (and anything I missed) is in place, then you could go
ahead and stop handling ret==0 cases at the call sites.
thanks,
--
John Hubbard
NVIDIA
Signed-off-by: Souptick Joarder <jrdr.linux@xxxxxxxxx>
---
arch/ia64/kernel/err_inject.c | 2 +-
drivers/platform/goldfish/goldfish_pipe.c | 2 +-
drivers/staging/gasket/gasket_page_table.c | 4 ++--
drivers/tee/tee_shm.c | 2 +-
mm/gup.c | 6 +++---
net/rds/rdma.c | 2 +-
6 files changed, 9 insertions(+), 9 deletions(-)
diff --git a/arch/ia64/kernel/err_inject.c b/arch/ia64/kernel/err_inject.c
index 8b5b8e6b..fd72218 100644
--- a/arch/ia64/kernel/err_inject.c
+++ b/arch/ia64/kernel/err_inject.c
@@ -143,7 +143,7 @@ static DEVICE_ATTR(name, 0644, show_##name, store_##name)
int ret;
ret = get_user_pages_fast(virt_addr, 1, FOLL_WRITE, NULL);
- if (ret<=0) {
+ if (ret < 0) {
#ifdef ERR_INJ_DEBUG
printk("Virtual address %lx is not existing.\n",virt_addr);
#endif
diff --git a/drivers/platform/goldfish/goldfish_pipe.c b/drivers/platform/goldfish/goldfish_pipe.c
index 1ab207e..831449d 100644
--- a/drivers/platform/goldfish/goldfish_pipe.c
+++ b/drivers/platform/goldfish/goldfish_pipe.c
@@ -277,7 +277,7 @@ static int goldfish_pin_pages(unsigned long first_page,
ret = pin_user_pages_fast(first_page, requested_pages,
!is_write ? FOLL_WRITE : 0,
pages);
- if (ret <= 0)
+ if (ret < 0)
return -EFAULT;
if (ret < requested_pages)
*iter_last_page_size = PAGE_SIZE;
diff --git a/drivers/staging/gasket/gasket_page_table.c b/drivers/staging/gasket/gasket_page_table.c
index f6d7157..1d08e1d 100644
--- a/drivers/staging/gasket/gasket_page_table.c
+++ b/drivers/staging/gasket/gasket_page_table.c
@@ -489,11 +489,11 @@ static int gasket_perform_mapping(struct gasket_page_table *pg_tbl,
ret = get_user_pages_fast(page_addr - offset, 1,
FOLL_WRITE, &page);
- if (ret <= 0) {
+ if (ret < 0) {
dev_err(pg_tbl->device,
"get user pages failed for addr=0x%lx, offset=0x%lx [ret=%d]\n",
page_addr, offset, ret);
- return ret ? ret : -ENOMEM;
+ return ret;
}
++pg_tbl->num_active_pages;
diff --git a/drivers/tee/tee_shm.c b/drivers/tee/tee_shm.c
index bd679b7..2706a1f 100644
--- a/drivers/tee/tee_shm.c
+++ b/drivers/tee/tee_shm.c
@@ -230,7 +230,7 @@ struct tee_shm *tee_shm_register(struct tee_context *ctx, unsigned long addr,
if (rc > 0)
shm->num_pages = rc;
if (rc != num_pages) {
- if (rc >= 0)
+ if (rc > 0)
rc = -ENOMEM;
ret = ERR_PTR(rc);
goto err;
diff --git a/mm/gup.c b/mm/gup.c
index 50681f0..8d293ed 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2760,7 +2760,7 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
end = start + len;
if (end <= start)
- return 0;
+ return -EINVAL;
if (unlikely(!access_ok((void __user *)start, len)))
return -EFAULT;
@@ -2805,8 +2805,8 @@ static int internal_get_user_pages_fast(unsigned long start, int nr_pages,
* calling get_user_pages().
*
* Returns number of pages pinned. This may be fewer than the number requested.
- * If nr_pages is 0 or negative, returns 0. If no pages were pinned, returns
- * -errno.
+ * If nr_pages is 0 or negative, returns -errno. If no pages were pinned,
+ * returns -errno.
*/
int get_user_pages_fast(unsigned long start, int nr_pages,
unsigned int gup_flags, struct page **pages)
diff --git a/net/rds/rdma.c b/net/rds/rdma.c
index a7ae118..44b96e6 100644
--- a/net/rds/rdma.c
+++ b/net/rds/rdma.c
@@ -161,7 +161,7 @@ static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages,
gup_flags |= FOLL_WRITE;
ret = pin_user_pages_fast(user_addr, nr_pages, gup_flags, pages);
- if (ret >= 0 && ret < nr_pages) {
+ if (ret > 0 && ret < nr_pages) {
unpin_user_pages(pages, ret);
ret = -EFAULT;
}
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