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a=z/mQ4Ysz8XfWz/Q5cLBRGdckG28=:19 a=lCpzRmAYbLLaTzLvsPZ7Mbvzbb8=:19 a=xqWC_Br6kY4A:10 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=GoEa3M9JfhUA:10 a=VkNPw1HP01LnGYTKEx00:22 a=jiCTI4zE5U7BLdzWsZGv:22 a=x4eqshVgHu-cdnggieHk:22 a=VwQbUJbxAAAA:8 a=pGLkceISAAAA:8 a=968KyxNXAAAA:8 a=Wow7f_iewQhk52Bz9CoA:9 a=QEXdDO2ut3YA:10 a=WmVTiCyuxqgg3mnwYu6p:22 X-Proofpoint-ORIG-GUID: Avdi0c7mkLzSs38m9LUOmJI5zlCUcB-o X-Proofpoint-GUID: Avdi0c7mkLzSs38m9LUOmJI5zlCUcB-o X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDE2MDAzOSBTYWx0ZWRfX9VCzD9uA+x7Q CfWl5qYVHcyy/wOh2k8StXO9pKrXzOnHBq/N4sggZxDAiF+afLPNIQjyZcbDLZAWeXh2qx7y4ic NjKNSs6WvTRFlyIWcAwmuK/j2/99yhc7QunP980c5MkNI6Aeg1Fp0zyTpdDaPcGtuR452O4+zNr +3sOZ4LJ8iVjnzTzPgO551DuPA4DdH1U+kt4bm3wfxMCZEMmB3dwp9nu/i5rTNPVfnne8wFItmH AHC8WvQKQX4XgSN3ufYs12XyNkqqSuXhF6pnhojrDcl2yEYxnSShn/gN9e5vA+lYMHGVzsS15Jc +jHubM+oe0BuGkWEeqI00Ts76J6qY1rzxA0prP+/PZXO6vU1CSdO901bFnocgRBnJVw3CDDA03K MJqIjmw1vAbYItawl52CPMKVK9yZ4KNw6CuJ4Vgb/eJv+ryy4dCjHcxJYSDYvi3UKSNA2fCPWET VRBGXHb79ZyWLFmduDw== X-Proofpoint-Spam-Info: AW1haW4tMjYxMDE2MDAzOSBTYWx0ZWRfX0OFdsAHF8xyM enAVvBb4SxuRjflnwDTI/RFNICHg4qgW4brPsBhxit/kv7+j3m9GVcZ/3O7BSvp0EToCxfTPip+ PLd3MRrH/YGN+MzlQLo40NqvKi9NsOrT0tqWN+AqIFUKOBAlF/t5 On 16/10/2026 06:49, Muchun Song wrote: > Static pmem Device DAX namespaces reserve space for namespace metadata before > the user-visible data range, and may also include padding needed to satisfy the > Device DAX alignment. __dax_pmem_probe() adjusts the dax_region range to start > at the > > Static pmem Device DAX namespaces reserve space for namespace metadata > before the user-visible data range, and may also include padding needed > to satisfy the Device DAX alignment. __dax_pmem_probe() adjusts the > dax_region range to start at the data range, but the dev_pagemap range > still starts at the beginning of the namespace. > > That is not valid for compound devmap mappings whose memmap is stored in > system RAM. Compound page initialization requires the start PFN to be > naturally aligned to the compound page size, because the head and tail > struct pages are initialized according to that geometry. If the pgmap > starts before the aligned data range, memmap_init_zone_device() can build > compound page metadata from an unaligned PFN. > > The resulting struct page layout is inconsistent with the Device DAX > mapping. A later mmap fault can then resolve the user-visible PFN through > invalid compound page metadata and hit a kernel panic while inserting the > DAX folio. > > Fix this by advancing the pgmap start to the aligned Device DAX data > range for non-altmap compound mappings. Leave base-page namespaces > unchanged, and leave the altmap path unchanged because > memmap_init_zone_device() already skips the altmap reservation itself. > > Fixes: 14606001efb4 ("device-dax: compound devmap support") > Cc: > Reported-by: Ritesh Harjani (IBM) > Closes: https://lore.kernel.org/r/wlrkqqvg.ritesh.list@gmail.com > Assisted-by: LLM > Signed-off-by: Muchun Song > ---> drivers/dax/pmem.c | 7 +++++++ > 1 file changed, 7 insertions(+) > > diff --git a/drivers/dax/pmem.c b/drivers/dax/pmem.c > index bee93066a849..d3a9b85107b0 100644 > --- a/drivers/dax/pmem.c > +++ b/drivers/dax/pmem.c > @@ -51,6 +51,13 @@ static struct dev_dax *__dax_pmem_probe(struct device *dev) > /* adjust the dax_region range to the start of data */ > range = pgmap.range; > range.start += offset; > + /* > + * When the memmap is stored in RAM, exclude metadata and alignment > + * padding from compound page initialization. Otherwise, the pgmap > + * may start before the naturally aligned Device DAX data range. > + */ > + if (!pgmap_altmap(&pgmap) && le32_to_cpu(pfn_sb->align) > PAGE_SIZE) > + pgmap.range.start = range.start; Should we need to check here for pgmap.type == MEMORY_DEVICE_GENERIC ? Considering the dedup is not quite applicable for FSDAX.