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b=sA83lo8ok1wmkMwr/ZGIZ2goQzDlXsCzamAyzAIvL99C/9JgPHezFE7D66o/bZT2x bDrZTOW0okeCLy7Oz1Rc/YwS38s+MHW24zMItGUNVTWAOWQGdgay1X67hb4ldKC93M JGP5NjPB3AW1W33lmewtdx4LUpUtIGzhW8OAc3fc= Date: Mon, 17 Aug 2026 15:35:01 -0700 From: Andrew Morton To: Foxie Flakey , rppt@kernel.org, peterx@redhat.com, linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] userfaultfd: reset err to be 0 when move_pages_ptes succeeded Message-Id: <20260817153501.ee2ee77976e1cd5b1e1c813b@linux-foundation.org> In-Reply-To: <20260817152605.5d2bee3fbf1a2bace4c0eff1@linux-foundation.org> References: <9c936a9f-ed27-e510-872f-5b3b8c680975@gmail.com> <20260817152605.5d2bee3fbf1a2bace4c0eff1@linux-foundation.org> X-Mailer: Sylpheed 3.8.0beta1 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Rspam-User: X-Stat-Signature: w99ga6ocmbyot49mpicozkr7wugq5e3a X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 24FDC40003 X-HE-Tag: 1787006102-112456 X-HE-Meta: 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 Fqiid/sB jXUyueBPoSztUjllun7tTuieziCPK66JUJ5lhgIvNnkPcW2VOGoBOnhytUaLTMDa/RsPp3usToZSE+4Bxn0Q7DxSQxdmAP9fqO8WcGXFZAMIs90JILi1eh9uQZTKg7EX2nWHzm6384CEiiRLzkAC+BPq3S+SUgdtgD3PfPV2VT3GAUfeU8Qc+iJT5mTR1KrMj9sw5qRTM2wMDxH5iI2V4B+HNwYI+XVRFGwsFa/e2XhkczwTQA58OJg2ISQQWyXOMHHJZHCpUay+phH4AGraeLabjLBd8ZYCJk08Yt9HwEyTQPihTjq2Y8tOhuswB1EOUTejptrj8LFp4brhLRyKrebtbRWyfQ7Te0UMk Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, 17 Aug 2026 15:26:05 -0700 Andrew Morton wrote: > > That behaviour manifested into this at userspace > > > > Source: [ .. unmapped .. ][ .. mapped ..] > > Destination: [ .. mapped .. ][ .. unmapped ..] > > ^ ^ > > \ Kernel moved this far in actuality > > What is reported to userspace on struct > > uffdio_move's move field > > > > When the previous behaviour is > > Source: [ .. unmapped .. ][ .. mapped ..] > > Destination: [ .. mapped .. ][ .. unmapped ..] > > ^ > > Reported to user space via uffdio_move's > > move field Also... I assume the above illuminates lack of coverage in the uffd selftests. Is it hard to add a case to detect this?