Re: [PATCHv2 1/2] mm/memory: Do not populate page table entries beyond i_size

[David Hildenbrand <david@redhat.com>]

On 23.10.25 22:49, Andrew Morton wrote:
> On Thu, 23 Oct 2025 10:32:50 +0100 Kiryl Shutsemau <kirill@shutemov.name> wrote:
> 
>> From: Kiryl Shutsemau <kas@kernel.org>
>>
>> Accesses within VMA, but beyond i_size rounded up to PAGE_SIZE are
>> supposed to generate SIGBUS.
>>
>> Recent changes attempted to fault in full folio where possible. They did
>> not respect i_size, which led to populating PTEs beyond i_size and
>> breaking SIGBUS semantics.
>>
>> Darrick reported generic/749 breakage because of this.
>>
>> However, the problem existed before the recent changes. With huge=always
>> tmpfs, any write to a file leads to PMD-size allocation. Following the
>> fault-in of the folio will install PMD mapping regardless of i_size.
>>
>> Fix filemap_map_pages() and finish_fault() to not install:
>>    - PTEs beyond i_size;
>>    - PMD mappings across i_size;
>>
>> Signed-off-by: Kiryl Shutsemau <kas@kernel.org>
>> Fixes: 19773df031bc ("mm/fault: try to map the entire file folio in finish_fault()")
> 
> Sep 28 2025
> 
>> Fixes: 357b92761d94 ("mm/filemap: map entire large folio faultaround")
> 
> Sep 28 2025
> 
>> Fixes: 800d8c63b2e9 ("shmem: add huge pages support")
> 
> Jul 26 2016
> 
> eek, what's this one doing here?  Are we asking -stable maintainers
> to backport this patch into nine years worth of kernels?
> 
> I'll remove this Fixes: line for now...

Ehm, why? It sure is a fix for that. We can indicate to which stable 
versions we want to have ti backported.

And yes, it might be all stable kernels.

-- 
Cheers

David / dhildenb