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drivers/mic/scif: convert get_user_pages() --> pin_user_pages()

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This code was using get_user_pages*(), in a "Case 2" scenario
(DMA/RDMA), using the categorization from [1]. That means that it's
time to convert the get_user_pages*() + put_page() calls to
pin_user_pages*() + unpin_user_pages() calls.

There is some helpful background in [2]: basically, this is a small
part of fixing a long-standing disconnect between pinning pages, and
file systems' use of those pages.

Note that this effectively changes the code's behavior as well: it now
ultimately calls set_page_dirty_lock(), instead of SetPageDirty(). 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." [3]

[1] Documentation/core-api/pin_user_pages.rst

[2] "Explicit pinning of user-space pages":
    https://lwn.net/Articles/807108/

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

Signed-off-by: John Hubbard <jhubbard@nvidia.com>
Link: https://lore.kernel.org/r/20200518041307.1987328-1-jhubbard@nvidia.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
John Hubbard 2020-05-17 21:13:07 -07:00 committed by Greg Kroah-Hartman
parent 6a0953ce7d
commit 5459ceedb3
1 changed files with 13 additions and 13 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

26
drivers/misc/mic/scif/scif_rma.c
View File

@ -113,14 +113,17 @@ static int scif_destroy_pinned_pages(struct scif_pinned_pages *pin)
int writeable = pin->prot & SCIF_PROT_WRITE;
int kernel = SCIF_MAP_KERNEL & pin->map_flags;
for (j = 0; j < pin->nr_pages; j++) {
if (pin->pages[j] && !kernel) {
if (writeable)
SetPageDirty(pin->pages[j]);
put_page(pin->pages[j]);
if (kernel) {
for (j = 0; j < pin->nr_pages; j++) {
if (pin->pages[j] && !kernel) {
if (writeable)
set_page_dirty_lock(pin->pages[j]);
put_page(pin->pages[j]);
}
}
}
} else
unpin_user_pages_dirty_lock(pin->pages, pin->nr_pages,
writeable);
scif_free(pin->pages,
pin->nr_pages * sizeof(*pin->pages));
scif_free(pin, sizeof(*pin));
@ -1375,7 +1378,7 @@ retry:
}
}
pinned_pages->nr_pages = get_user_pages_fast(
pinned_pages->nr_pages = pin_user_pages_fast(
(u64)addr,
nr_pages,
(prot & SCIF_PROT_WRITE) ? FOLL_WRITE : 0,
@ -1385,11 +1388,8 @@ retry:
if (ulimit)
__scif_dec_pinned_vm_lock(mm, nr_pages);
/* Roll back any pinned pages */
for (i = 0; i < pinned_pages->nr_pages; i++) {
if (pinned_pages->pages[i])
put_page(
pinned_pages->pages[i]);
}
unpin_user_pages(pinned_pages->pages,
pinned_pages->nr_pages);
prot &= ~SCIF_PROT_WRITE;
try_upgrade = false;
goto retry;