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authorAlistair Popple <apopple@nvidia.com>2021-06-30 18:54:25 -0700
committerLinus Torvalds <torvalds@linux-foundation.org>2021-07-01 11:06:03 -0700
commitb756a3b5e7ead8f6f4b03cea8ac22478ce04c8a8 (patch)
treefc6e3f788e1144e48ddc15475dc18d44448d6e22 /include/linux/rmap.h
parent9a5cc85c407402ae66128d31f0422a3a7ffa5c5c (diff)
downloadlwn-b756a3b5e7ead8f6f4b03cea8ac22478ce04c8a8.tar.gz
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mm: device exclusive memory access
Some devices require exclusive write access to shared virtual memory (SVM) ranges to perform atomic operations on that memory. This requires CPU page tables to be updated to deny access whilst atomic operations are occurring. In order to do this introduce a new swap entry type (SWP_DEVICE_EXCLUSIVE). When a SVM range needs to be marked for exclusive access by a device all page table mappings for the particular range are replaced with device exclusive swap entries. This causes any CPU access to the page to result in a fault. Faults are resovled by replacing the faulting entry with the original mapping. This results in MMU notifiers being called which a driver uses to update access permissions such as revoking atomic access. After notifiers have been called the device will no longer have exclusive access to the region. Walking of the page tables to find the target pages is handled by get_user_pages() rather than a direct page table walk. A direct page table walk similar to what migrate_vma_collect()/unmap() does could also have been utilised. However this resulted in more code similar in functionality to what get_user_pages() provides as page faulting is required to make the PTEs present and to break COW. [dan.carpenter@oracle.com: fix signedness bug in make_device_exclusive_range()] Link: https://lkml.kernel.org/r/YNIz5NVnZ5GiZ3u1@mwanda Link: https://lkml.kernel.org/r/20210616105937.23201-8-apopple@nvidia.com Signed-off-by: Alistair Popple <apopple@nvidia.com> Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com> Reviewed-by: Christoph Hellwig <hch@lst.de> Cc: Ben Skeggs <bskeggs@redhat.com> Cc: Hugh Dickins <hughd@google.com> Cc: Jason Gunthorpe <jgg@nvidia.com> Cc: John Hubbard <jhubbard@nvidia.com> Cc: "Matthew Wilcox (Oracle)" <willy@infradead.org> Cc: Peter Xu <peterx@redhat.com> Cc: Ralph Campbell <rcampbell@nvidia.com> Cc: Shakeel Butt <shakeelb@google.com> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Diffstat (limited to 'include/linux/rmap.h')
-rw-r--r--include/linux/rmap.h4
1 files changed, 4 insertions, 0 deletions
diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index b0ea9d98302f..83fb86133fe1 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -194,6 +194,10 @@ int page_referenced(struct page *, int is_locked,
void try_to_migrate(struct page *page, enum ttu_flags flags);
void try_to_unmap(struct page *, enum ttu_flags flags);
+int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
+ unsigned long end, struct page **pages,
+ void *arg);
+
/* Avoid racy checks */
#define PVMW_SYNC (1 << 0)
/* Look for migarion entries rather than present PTEs */