Hello,
This was a well known issue for more than a decade, but until a few
months ago we relied on the compiler to stick to atomic accesses and
updates while walking and updating pagetables.
However now the 64bit native_set_pte finally uses WRITE_ONCE and
gup_pmd_range uses READ_ONCE as well.
This convert more racy VM places to avoid depending on the expected
compiler behavior to achieve kernel runtime correctness.
It mostly guarantees gcc to do atomic updates at 64bit granularity
(practically not needed) and it also prevents gcc to emit code that
risks getting confused if the memory unexpectedly changes under it
(unlikely to ever be needed).
The list of vm_start/end/pgoff to update isn't complete, I covered the
most obvious places, but before wasting too much time at doing a full
audit I thought it was safer to post it and get some comment. More
updates can be posted incrementally anyway.
Andrea Arcangeli (2):
coredump: use READ_ONCE to read mm->flags
mm: use READ/WRITE_ONCE to access anonymous vmas
vm_start/vm_end/vm_pgoff
fs/coredump.c | 2 +-
mm/gup.c | 23 +++++++++++++----------
mm/internal.h | 3 ++-
mm/memory.c | 2 +-
mm/mmap.c | 16 ++++++++--------
mm/rmap.c | 3 ++-
mm/vmacache.c | 3 ++-
7 files changed, 29 insertions(+), 23 deletions(-)
