> From: Alistair Popple <[email protected]> > Sent: Thursday, February 25, 2021 11:18 PM > To: [email protected]; [email protected]; > [email protected]; [email protected] > Cc: [email protected]; [email protected]; dri- > [email protected]; John Hubbard <[email protected]>; Ralph > Campbell <[email protected]>; [email protected]; Jason Gunthorpe > <[email protected]>; [email protected]; [email protected]; Alistair Popple > <[email protected]> > Subject: [PATCH v3 5/8] 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. > > Signed-off-by: Alistair Popple <[email protected]> > --- > Documentation/vm/hmm.rst | 15 ++++ > include/linux/rmap.h | 3 + > include/linux/swap.h | 4 +- > include/linux/swapops.h | 44 ++++++++++- > mm/hmm.c | 5 ++ > mm/memory.c | 108 +++++++++++++++++++++++++- > mm/mprotect.c | 8 ++ > mm/page_vma_mapped.c | 9 ++- > mm/rmap.c | 163 +++++++++++++++++++++++++++++++++++++++ > 9 files changed, 352 insertions(+), 7 deletions(-) ... > +int make_device_exclusive_range(struct mm_struct *mm, unsigned long start, > + unsigned long end, struct page **pages) { > + long npages = (end - start) >> PAGE_SHIFT; > + long i;
Nit: you should use unsigned long for 'i' and 'npages' to match start/end.
