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| author | York Jasper Niebuhr <yjnworkstation@gmail.com> | 2023-11-11 21:48:59 +0300 |
|---|---|---|
| committer | Andrew Morton <akpm@linux-foundation.org> | 2023-12-11 03:51:39 +0300 |
| commit | 932b59e3beaefefb1a0bd65f1bb3f9e2000d7315 (patch) | |
| tree | 945384e2b149af740329e30b1be43cb8413acaf6 /mm/process_vm_access.c | |
| parent | 69e583eaca579d50ffc699b1f4358258e75fa008 (diff) | |
| download | linux-932b59e3beaefefb1a0bd65f1bb3f9e2000d7315.tar.xz | |
mm: fix process_vm_rw page counts
1. There is a "-1" missing in the page number calculation in
process_vm_rw_core. While this can't break anything, it can cause
unnecessary allocations in certain cases:
Consider handling an iovec ranging over PVM_MAX_PP_ARRAY_COUNT pages
that is also aligned to a page boundary. While pp_stack could hold
references to such an amount of pinned pages, nr_pages yields
(PVM_MAX_PP_ARRAY + 1) in process_vm_rw_core. Consequently, a larger
buffer is allocated with kmalloc for no reason.
For any page boundary aligned iovec that is a multiple of PAGE_SIZE
and larger than PVM_MAX_PP_ARRAY_COUNT pages, nr_pages will be too big
by 1 and thus kmalloc allocates excess space for one more pointer.
2. max_pages_per_loop is constant and there is no reason to have it as
a variable. A macro does the job just fine and saves memory.
3. Replaced "sizeof(struct pages *)" with "sizeof(struct page *)" to
have matching types for allocation and prevent confusion.
Link: https://lkml.kernel.org/r/20231111184859.44264-1-yjnworkstation@gmail.com
Signed-off-by: York Jasper Niebuhr <yjnworkstation@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Diffstat (limited to 'mm/process_vm_access.c')
| -rw-r--r-- | mm/process_vm_access.c | 15 |
1 files changed, 8 insertions, 7 deletions
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c index 0523edab03a6..b308e96cd05a 100644 --- a/mm/process_vm_access.c +++ b/mm/process_vm_access.c @@ -53,7 +53,10 @@ static int process_vm_rw_pages(struct page **pages, } /* Maximum number of pages kmalloc'd to hold struct page's during copy */ -#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2) +#define PVM_MAX_KMALLOC_PAGES 2 + +/* Maximum number of pages that can be stored at a time */ +#define PVM_MAX_USER_PAGES (PVM_MAX_KMALLOC_PAGES * PAGE_SIZE / sizeof(struct page *)) /** * process_vm_rw_single_vec - read/write pages from task specified @@ -79,8 +82,6 @@ static int process_vm_rw_single_vec(unsigned long addr, unsigned long start_offset = addr - pa; unsigned long nr_pages; ssize_t rc = 0; - unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES - / sizeof(struct pages *); unsigned int flags = 0; /* Work out address and page range required */ @@ -92,7 +93,7 @@ static int process_vm_rw_single_vec(unsigned long addr, flags |= FOLL_WRITE; while (!rc && nr_pages && iov_iter_count(iter)) { - int pinned_pages = min(nr_pages, max_pages_per_loop); + int pinned_pages = min_t(unsigned long, nr_pages, PVM_MAX_USER_PAGES); int locked = 1; size_t bytes; @@ -171,7 +172,7 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter, iov_len = rvec[i].iov_len; if (iov_len > 0) { nr_pages_iov = ((unsigned long)rvec[i].iov_base - + iov_len) + + iov_len - 1) / PAGE_SIZE - (unsigned long)rvec[i].iov_base / PAGE_SIZE + 1; nr_pages = max(nr_pages, nr_pages_iov); @@ -184,8 +185,8 @@ static ssize_t process_vm_rw_core(pid_t pid, struct iov_iter *iter, if (nr_pages > PVM_MAX_PP_ARRAY_COUNT) { /* For reliability don't try to kmalloc more than 2 pages worth */ - process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES, - sizeof(struct pages *)*nr_pages), + process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES * PAGE_SIZE, + sizeof(struct page *)*nr_pages), GFP_KERNEL); if (!process_pages) |