Re: [PATCH 6.17.y] mm/truncate: unmap large folio on split failure

[Greg KH <gregkh@linuxfoundation.org>]

On Thu, Nov 20, 2025 at 04:52:21PM +0000, Kiryl Shutsemau wrote:
> Accesses within VMA, but beyond i_size rounded up to PAGE_SIZE are
> supposed to generate SIGBUS.
> 
> This behavior might not be respected on truncation.
> 
> During truncation, the kernel splits a large folio in order to reclaim
> memory.  As a side effect, it unmaps the folio and destroys PMD mappings
> of the folio.  The folio will be refaulted as PTEs and SIGBUS semantics
> are preserved.
> 
> However, if the split fails, PMD mappings are preserved and the user will
> not receive SIGBUS on any accesses within the PMD.
> 
> Unmap the folio on split failure.  It will lead to refault as PTEs and
> preserve SIGBUS semantics.
> 
> Make an exception for shmem/tmpfs that for long time intentionally mapped
> with PMDs across i_size.
> 
> Link: https://lkml.kernel.org/r/20251027115636.82382-3-kirill@shutemov.name
> Fixes: b9a8a4195c7d ("truncate,shmem: Handle truncates that split large folios")
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Cc: Baolin Wang <baolin.wang@linux.alibaba.com>
> Cc: Christian Brauner <brauner@kernel.org>
> Cc: "Darrick J. Wong" <djwong@kernel.org>
> Cc: Dave Chinner <david@fromorbit.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Hugh Dickins <hughd@google.com>
> Cc: Johannes Weiner <hannes@cmpxchg.org>
> Cc: Liam Howlett <liam.howlett@oracle.com>
> Cc: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Rapoport <rppt@kernel.org>
> Cc: Rik van Riel <riel@surriel.com>
> Cc: Shakeel Butt <shakeel.butt@linux.dev>
> Cc: Suren Baghdasaryan <surenb@google.com>
> Cc: Vlastimil Babka <vbabka@suse.cz>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> (cherry picked from commit fa04f5b60fda62c98a53a60de3a1e763f11feb41)
> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
> ---

Does not apply to 6.17.y at all :(

Did you forget to apply this on top of other commits?

thanks,

greg k-h