| Message ID | 20220331042137.6F5B6C340F0@smtp.kernel.org |
|---|---|
| State | New |
| Headers | show |
| Series | + mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0.patch added to -mm tree | expand |
--- a/mm/mremap.c~mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0 +++ a/mm/mremap.c @@ -486,6 +486,9 @@ unsigned long move_page_tables(struct vm pmd_t *old_pmd, *new_pmd; pud_t *old_pud, *new_pud; + if (!len) + return 0; + old_end = old_addr + len; flush_cache_range(vma, old_addr, old_end);
The patch titled Subject: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) has been added to the -mm tree. Its filename is mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0.patch This patch should soon appear at https://ozlabs.org/~akpm/mmots/broken-out/mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0.patch and later at https://ozlabs.org/~akpm/mmotm/broken-out/mm-avoid-pointless-invalidate_range_start-end-on-mremapold_size=0.patch Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next and is updated there every 3-4 working days ------------------------------------------------------ From: Paolo Bonzini <pbonzini@redhat.com> Subject: mmmremap.c: avoid pointless invalidate_range_start/end on mremap(old_size=0) If an mremap() syscall with old_size=0 ends up in move_page_tables(), it will call invalidate_range_start()/invalidate_range_end() unnecessarily, i.e. with an empty range. This causes a WARN in KVM's mmu_notifier. In the past, empty ranges have been diagnosed to be off-by-one bugs, hence the WARNing. Given the low (so far) number of unique reports, the benefits of detecting more buggy callers seem to outweigh the cost of having to fix cases such as this one, where userspace is doing something silly. In this particular case, an early return from move_page_tables() is enough to fix the issue. Link: https://lkml.kernel.org/r/20220329173155.172439-1-pbonzini@redhat.com Reported-by: syzbot+6bde52d89cfdf9f61425@syzkaller.appspotmail.com Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Cc: Sean Christopherson <seanjc@google.com> Cc: <stable@vger.kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> --- mm/mremap.c | 3 +++ 1 file changed, 3 insertions(+)