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Mon, 13 Apr 2026 05:53:05 -0700 (PDT) Received: from x1.local ([142.189.10.167]) by smtp.gmail.com with ESMTPSA id af79cd13be357-8ddb8d6dd41sm864313685a.25.2026.04.13.05.53.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 13 Apr 2026 05:53:04 -0700 (PDT) Date: Mon, 13 Apr 2026 08:53:03 -0400 From: Peter Xu To: Mike Rapoport Cc: David CARLIER , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Andrea Arcangeli Subject: Re: [PATCH v4] mm/userfaultfd: detect VMA replacement after copy retry in mfill_copy_folio_retry() Message-ID: References: <20260331134158.622084-1-devnexen@gmail.com> <20260331200148.cc0c95deaf070579a68af041@linux-foundation.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On Sun, Apr 12, 2026 at 06:46:17PM +0300, Mike Rapoport wrote: > > Personally this is least of a concern to me. Hugetlbfs is so specially > > managed in userapps, so it is even less likely to trigger the same bug with > > VM_SOFTDIRTY changes or other ways. > > I'm not sure I follow you here. How changes of VM_SOFTDIRTY can crash the > kernel in UFFDIO_COPY? It was confusing indeed that I used as example, sorry. SOFTDIRTY only case isn't a bug, even if it'll also be captured by "vma changes" when we detect that. I just wanted to say I concerned much less on arbitrary hugetlbfs vmas appearing than most of the rest, where it can crash the kernel even after the change (e.g. mapped one shmem inode, remapped to another different shmem inode, or SHARED->PRIVATE, as others pointed out elsewhere). > > > Again, I'm open to any suggestion on replacing the vma snapshot logic as > > long as all possible issues got reported will be properly fixed, especially > > in the latest mainline. I don't worry much on backporting yet; if this bug > > existed for 10 years and nobody yet reported, to me we can always evaluate > > the effort to backport or skip. However, a proper fix in mainline is IMHO > > more important. > > Totally agree, a fix in mainline is much more important than backporting. Thanks, -- Peter Xu