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a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=kj9zAlcOel0A:10 a=6UeiqGixMTsA:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=yPCof4ZbAAAA:8 a=VwQbUJbxAAAA:8 a=GDoLJOjFvT-abBd5_6wA:9 a=CjuIK1q_8ugA:10 X-Proofpoint-ORIG-GUID: oRrUKbIQEZ0EA_eaIOvoSZscAEcdokxP X-Proofpoint-Spam-Details-Enc: AW1haW4tMjUxMTE1MDAzMiBTYWx0ZWRfXzxYdvfD3Okgs 6c3+zBj5/AcRwkHmAAejb9AUVY71jrjWfnv3ubCWORDVoGIvQTeQ9Mmtm62tJ+xGvL6vDEWNRc2 P1MJOSExmmAzRluR2vVSh1/u/uuinc8+ApzjKf/0A9xUSdbpP30rFT4UyD2o9VPhWakULCXG6NV KM5X8oPI+1j4sS00cMlf4mtO0uhUWfSOGYRwq/nmdtdXlRrWyPhy77P//rjB2RqFE0NI16O3xZf q9hJl3W1YgjjsfVTY9okWUS2Zptv6mdPfDZ4Yr8rpaUhj5PPjnPvmHLqVLlXuc3KUfUSoNBzDes cy3g1MChNn5SXqPQHtO3P94tkshjxjAK88cG2U+RKDuBfdkqv0Oz3FvspRBMsRLiGFmj2HppZhm YLmQ6+fejDBHrNv7yP3ykOInWDyAxQ== On Mon, Nov 17, 2025 at 04:11:47PM +0100, David Hildenbrand (Red Hat) wrote: > On 07.11.25 17:11, Lorenzo Stoakes wrote: > > Currently, if a user needs to determine if guard regions are present in a > > range, they have to scan all VMAs (or have knowledge of which ones might > > have guard regions). > > > > Since commit 8e2f2aeb8b48 ("fs/proc/task_mmu: add guard region bit to > > pagemap") and the related commit a516403787e0 ("fs/proc: extend the > > PAGEMAP_SCAN ioctl to report guard regions"), users can use either > > /proc/$pid/pagemap or the PAGEMAP_SCAN functionality to perform this > > operation at a virtual address level. > > > > This is not ideal, and it gives no visibility at a /proc/$pid/smaps level > > that guard regions exist in ranges. > > > > This patch remedies the situation by establishing a new VMA flag, > > VM_MAYBE_GUARD, to indicate that a VMA may contain guard regions (it is > > uncertain because we cannot reasonably determine whether a > > MADV_GUARD_REMOVE call has removed all of the guard regions in a VMA, and > > additionally VMAs may change across merge/split). > > > > We utilise 0x800 for this flag which makes it available to 32-bit > > architectures also, a flag that was previously used by VM_DENYWRITE, which > > was removed in commit 8d0920bde5eb ("mm: remove VM_DENYWRITE") and hasn't > > bee reused yet. > > > > We also update the smaps logic and documentation to identify these VMAs. > > > > Another major use of this functionality is that we can use it to identify > > that we ought to copy page tables on fork. > > > > We do not actually implement usage of this flag in mm/madvise.c yet as we > > need to allow some VMA flags to be applied atomically under mmap/VMA read > > lock in order to avoid the need to acquire a write lock for this purpose. > > > > Reviewed-by: Pedro Falcato > > Reviewed-by: Vlastimil Babka > > Signed-off-by: Lorenzo Stoakes > > --- > > Documentation/filesystems/proc.rst | 5 +++-- > > fs/proc/task_mmu.c | 1 + > > include/linux/mm.h | 3 +++ > > include/trace/events/mmflags.h | 1 + > > mm/memory.c | 4 ++++ > > tools/testing/vma/vma_internal.h | 1 + > > 6 files changed, 13 insertions(+), 2 deletions(-) > > > > diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst > > index 0b86a8022fa1..8256e857e2d7 100644 > > --- a/Documentation/filesystems/proc.rst > > +++ b/Documentation/filesystems/proc.rst > > @@ -553,7 +553,7 @@ otherwise. > > kernel flags associated with the particular virtual memory area in two letter > > encoded manner. The codes are the following: > > - == ======================================= > > + == ============================================================= > > rd readable > > wr writeable > > ex executable > > @@ -591,7 +591,8 @@ encoded manner. The codes are the following: > > sl sealed > > lf lock on fault pages > > dp always lazily freeable mapping > > - == ======================================= > > + gu maybe contains guard regions (if not set, definitely doesn't) > > + == ============================================================= > > > In general LGTM, BUT in the context of this patch where the flag is never > set, that's not entirely correct ;) It made sense after staring at patch #5. Yeah I realise that's a bit of compromise but I think relatively benign in order to split up the series sensibly :) > > Acked-by: David Hildenbrand (Red Hat) Thanks! > > -- > Cheers > > David Cheers, Lorenzo