Re: [PATCH 2/2] mm/truncate: Unmap large folio on split failure

[Kiryl Shutsemau <kirill@shutemov.name>]

On Tue, Oct 21, 2025 at 11:47:11AM +0200, David Hildenbrand wrote:
> On 21.10.25 11:44, David Hildenbrand wrote:
> > On 21.10.25 08:35, Kiryl Shutsemau wrote:
> > > From: Kiryl Shutsemau <kas@kernel.org>
> > > 
> > > 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.
> > 
> > Was the discussion on the old patch set already done? I can spot that
> > you send this series 20min after asking Dave

Based on feedback from Dave and Christoph on this patchset as well as
comments form Matthew and Darrick ont the report thread I see that my
idea to relax SIGBUS semantics for large folios will not fly :/

But if you want to weigh in...

> Also, please send a proper patch series including cover letter that
> describes the changes since the last RFC.

There is no change besides Signed-off-bys.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov