While reviewing Baoquan's recent changes to permit vread() access to vm_map_ram regions of vmalloc allocations, Willy pointed out [1] that it would be nice to refactor vread() as a whole, since its only user is read_kcore() and the existing form of vread() necessitates the use of a bounce buffer. This patch series does exactly that, as well as adjusting how we read the kernel text section to avoid the use of a bounce buffer in this case as well. This has been tested against the test case which motivated Baoquan's changes in the first place [2] which continues to function correctly, as do the vmalloc self tests. [1] https://lore.kernel.org/all/Y8WfDSRkc%2FOHP3oD@xxxxxxxxxxxxxxxxxxxx/ [2] https://lore.kernel.org/all/87ilk6gos2.fsf@xxxxxxxxxx/T/#u v8: - Make zero_iter() static. v7: - Keep trying to fault in memory until the vmalloc read operation completes. https://lore.kernel.org/all/cover.1679511146.git.lstoakes@xxxxxxxxx/ v6: - Correct copy_page_to_iter_nofault() to handle -EFAULT case correctly. https://lore.kernel.org/all/cover.1679496827.git.lstoakes@xxxxxxxxx/ v5: - Do not rename fpos to ppos in read_kcore_iter() to avoid churn. - Fix incorrect commit messages after prior revisions altered the approach. - Replace copy_page_to_iter_atomic() with copy_page_to_iter_nofault() and adjust it to be able to handle compound pages. This uses copy_to_user_nofault() which ensures page faults are disabled during copy which kmap_local_page() was not doing. - Only try to fault in pages if we are unable to copy in the first place and try only once to avoid any risk of spinning. - Do not zero memory in aligned_vread_iter() if we couldn't copy it. - Fix mistake in zeroing missing or unpopulated blocks in vmap_ram_vread_iter(). https://lore.kernel.org/linux-mm/cover.1679494218.git.lstoakes@xxxxxxxxx/ v4: - Fixup mistake in email client which orphaned patch emails from the cover letter. https://lore.kernel.org/all/cover.1679431886.git.lstoakes@xxxxxxxxx v3: - Revert introduction of mutex/rwsem in vmalloc - Introduce copy_page_to_iter_atomic() iovec function - Update vread_iter() and descendent functions to use only this - Fault in user pages before calling vread_iter() - Use const char* in vread_iter() and descendent functions - Updated commit messages based on feedback - Extend vread functions to always check how many bytes we could copy. If at any stage we are unable to copy/zero, abort and return the number of bytes we did copy. https://lore.kernel.org/all/cover.1679354384.git.lstoakes@xxxxxxxxx/ v2: - Fix ordering of vread_iter() parameters - Fix nommu vread() -> vread_iter() https://lore.kernel.org/all/cover.1679209395.git.lstoakes@xxxxxxxxx/ v1: https://lore.kernel.org/all/cover.1679183626.git.lstoakes@xxxxxxxxx/ Lorenzo Stoakes (4): fs/proc/kcore: avoid bounce buffer for ktext data fs/proc/kcore: convert read_kcore() to read_kcore_iter() iov_iter: add copy_page_to_iter_nofault() mm: vmalloc: convert vread() to vread_iter() fs/proc/kcore.c | 85 +++++++-------- include/linux/uio.h | 2 + include/linux/vmalloc.h | 3 +- lib/iov_iter.c | 48 +++++++++ mm/nommu.c | 10 +- mm/vmalloc.c | 234 +++++++++++++++++++++++++--------------- 6 files changed, 243 insertions(+), 139 deletions(-) -- 2.39.2
