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Wed, 01 Apr 2026 22:59:26 -0700 (PDT) MIME-Version: 1.0 References: <20260331134158.622084-1-devnexen@gmail.com> <20260331200148.cc0c95deaf070579a68af041@linux-foundation.org> In-Reply-To: From: David CARLIER Date: Thu, 2 Apr 2026 06:59:13 +0100 X-Gm-Features: AQROBzBgRWyqJogYNVMiyiFDybYk9gqvdSpOKXfZ0-indKq42_N1Bv98LXessEg Message-ID: Subject: Re: [PATCH v4] mm/userfaultfd: detect VMA replacement after copy retry in mfill_copy_folio_retry() To: Mike Rapoport Cc: Peter Xu , Andrew Morton , linux-mm@kvack.org, linux-kernel@vger.kernel.org, Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka Content-Type: text/plain; charset="UTF-8" X-Stat-Signature: 6n853d4z67q1ass3zigtj38rjpcsobk7 X-Rspamd-Queue-Id: 40F444000B X-Rspam-User: X-Rspamd-Server: rspam03 X-HE-Tag: 1775109567-234196 X-HE-Meta: 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 jy/CVJ06 peGQHIap4LYTdAD7xkg/K0otGxy9D9xLR/bhYoXpVjDxaiTSPdSbwC9sauazXmhHNnlr88H1PZ7C4ATwjZrymLcwA4yLQu7o7kd0gbPSWEjMe1p4= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Understood on all points. Will rework patch 1 to a simple ops comparison with -ENOENT, drop vma_snapshot entirely. Will cc MEMORY MAPPING folks. Holding off until after -rc1, will resend both then. Cheers. On Thu, 2 Apr 2026 at 05:02, Mike Rapoport wrote: > > On Wed, Apr 01, 2026 at 03:22:03PM -0400, Peter Xu wrote: > > > > The other thing is I just noticed the err code was changed to -EINVAL for > > snapshot changed cases, sorry I didn't follow previously as closely on the > > discussion. I think it should be -EAGAIN. It's because the userapp can't > > resolve -EINVAL failures and app will crash. In a VMA change use case, we > > should return -EAGAIN to imply the app to retry, rather than crashing. > > No. The return value should express that the VMA is invalid. -EINVAL could > work, but looking now at the manual -ENOENT would be even better: > > ENOENT (since Linux 4.11) > The faulting process has changed its virtual memory layout > simultaneously with an outstanding UFFDIO_COPY operation. > > > Thanks, > > -- > > Peter Xu > > -- > Sincerely yours, > Mike.