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List-Subscribe: List-Unsubscribe: Andrew - to be clear, this should be a hotfix against 6.16-rc1 :>) Thanks! On Mon, Jun 09, 2025 at 12:18:40PM +0200, Vlastimil Babka wrote: > On 6/9/25 11:24 AM, Lorenzo Stoakes wrote: > > Nested file systems, that is those which invoke call_mmap() within their > > own f_op->mmap() handlers, may encounter underlying file systems which > > provide the f_op->mmap_prepare() hook introduced by commit > > c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file callback"). > > > > We have a chicken-and-egg scenario here - until all file systems are > > converted to using .mmap_prepare(), we cannot convert these nested > > handlers, as we can't call f_op->mmap from an .mmap_prepare() hook. > > > > So we have to do it the other way round - invoke the .mmap_prepare() hook > > from an .mmap() one. > > > > in order to do so, we need to convert VMA state into a struct vm_area_desc > > descriptor, invoking the underlying file system's f_op->mmap_prepare() > > callback passing a pointer to this, and then setting VMA state accordingly > > and safely. > > > > This patch achieves this via the compat_vma_mmap_prepare() function, which > > we invoke from call_mmap() if f_op->mmap_prepare() is specified in the > > passed in file pointer. > > > > We place the fundamental logic into mm/vma.c where VMA manipulation > > belongs. We also update the VMA userland tests to accommodate the changes. > > > > The compat_vma_mmap_prepare() function and its associated machinery is > > temporary, and will be removed once the conversion of file systems is > > complete. > > > > Signed-off-by: Lorenzo Stoakes > > Reported-by: Jann Horn > > Closes: https://lore.kernel.org/linux-mm/CAG48ez04yOEVx1ekzOChARDDBZzAKwet8PEoPM4Ln3_rk91AzQ@mail.gmail.com/ > > Fixes: c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file callback"). > > So this is a hotfix for 6.16-rc1 but doesn't need cc: stable. > Also probably nothing wraps yet the filesystems with .mmap_prepare? But > good to have this handled within 6.16. Only secretmem uses this so unaffected BUT I want to make changes to filesystems in 6.17 which is blocked by this problem (I actually have a bunch of changes queued up ready), so it's really important to get this hotfixed. Also, given the change in use of callback is going to touch a ton of filesystems this is important for backporting purposes, in case anything needs backporting there. So from that point of view it's important to have it in 6.16 also. > > Reviewed-by: Vlastimil Babka > Thanks!