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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> |
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| .. | ||
| .gitignore | ||
| active_mm.rst | ||
| arch_pgtable_helpers.rst | ||
| balance.rst | ||
| cleancache.rst | ||
| free_page_reporting.rst | ||
| frontswap.rst | ||
| highmem.rst | ||
| hmm.rst | ||
| hugetlbfs_reserv.rst | ||
| hwpoison.rst | ||
| index.rst | ||
| ksm.rst | ||
| memory-model.rst | ||
| mmu_notifier.rst | ||
| numa.rst | ||
| overcommit-accounting.rst | ||
| page_frags.rst | ||
| page_migration.rst | ||
| page_owner.rst | ||
| remap_file_pages.rst | ||
| slub.rst | ||
| split_page_table_lock.rst | ||
| swap_numa.rst | ||
| transhuge.rst | ||
| unevictable-lru.rst | ||
| z3fold.rst | ||
| zsmalloc.rst | ||
| zswap.rst | ||