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Karpov" Date: Thu, 9 Apr 2026 18:54:08 +0300 X-Gm-Features: AQROBzBmxDixh3DrVoiXKIPzHCcdgrsRneVlA9XfDga7WmsEQ-NmJ1QJsl6YSiA Message-ID: Subject: Re: [PATCH v2] userfaultfd: allow registration of ranges below mmap_min_addr To: Mike Rapoport Cc: Pedro Falcato , harry@kernel.org, akpm@linux-foundation.org, Liam.Howlett@oracle.com, ljs@kernel.org, vbabka@kernel.org, jannh@google.com, peterx@redhat.com, brauner@kernel.org, viro@zeniv.linux.org.uk, jack@suse.cz, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, usama.arif@linux.dev Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable X-Rspamd-Queue-Id: 89F2912000D X-Stat-Signature: sxjgf1mury9sb4t99tw9uwau1kofz6qy X-Rspam-User: X-Rspamd-Server: rspam04 X-HE-Tag: 1775750062-488260 X-HE-Meta: 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 /NQGU9Ri 4ZjEeaJk6QINPShXy3YKT5d4wtYPbZC/XSBmtW/C8clDuYMcz5sswe2+fSTbUf56IcBFEqZqNGGip78N8ZBX+jJydgEJC7+639BzxLlMPe9FAN12xiHMYCmG2qATDNuz7KmIB/aIq3gkbg4b94QXkaXraJ0VG3HxcJU+WGO3+Fb3DChoeZfVKqLsUTd5nvT8T7HhcPquPcosUX+1q8kLwLcoN3drEOdd/iPHV2onblSpfaaPpCVwpLdgr8EmWkA1GZcG4+YHtKa9BDDm8sGhDLsj8JlTFyl6sntF8nSfM7u7e3zNEjHZDIIjq+8p4hVskfbL70/p7/pqN++KtCwf15Xc+Abqvv2S2RI7F498x4xst5tJ/NROArfzcP4bWjBn6A4JMsEHpcOPablaggPIwihSxXcd42I0tCdtBYkjbJXhbTTyi0+C5p0rJceP4Uee0FU4/XfoIUiyW0VzS1rtOaQXDfw== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 9, 2026 at 6:17=E2=80=AFPM Mike Rapoport wrot= e: > On Thu, Apr 09, 2026 at 01:30:07PM +0100, Pedro Falcato wrote: > > This looks relatively safe. However, I'm not sure if we want this in st= able. > > This has been broken for 11 years now, with no complaints. > > I believe Denis has a new usecase that wasn't there for those 11 years :) > > Denis, can you share more details about your usecase for us to better > understand importance of backporting this to stable? Hello Mike. Actually, there is nothing new about the use case. We simply started using UFFD instead of the classic mprotect approach in the binary translator to track application writes. During development, we encountered this bug. The translator cannot control where the translated application chooses to map its memory and if the app requires a low-address area, UFFD fails, whereas mprotect would work just fine. I believe this is a genuine logic bug rather= than an improvement, and I would appreciate including the fix in stable.