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Wed, 21 Oct 2026 04:55:51 -0400 (EDT) Date: Wed, 21 Oct 2026 09:55:50 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Lance Yang , samarth.colleges@gmail.com, akpm@linux-foundation.org, xu.xin@linux.dev, chengming.zhou@linux.dev, peterx@redhat.com, rppt@kernel.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, stable@vger.kernel.org Subject: Re: [PATCH v2] mm/ksm: keep soft-dirty and uffd-wp when merging a page Message-ID: References: <20261020055518.36087-1-lance.yang@linux.dev> <3da45e6d-2b46-4fff-9ff3-241f70d68296@kernel.org> <68f17ee7-d272-4475-8a59-645442e2c210@kernel.org> X-Archived-By: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <68f17ee7-d272-4475-8a59-645442e2c210@kernel.org> X-Rspamd-Queue-Id: AB14280006 X-Rspam-User: X-Stat-Signature: ftgozp3m4madzi7ftgycad8xpd8cg4mq X-Spam-Status: No, score=-6.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_PASS,SPF_PASS autolearn=no autolearn_force=no version=4.0.1 X-Rspamd-Server: rspam03 X-HE-Tag: 1792572957-811452 X-HE-Meta: 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 SINrqPH4 PV0hEqVegnOYxcBRJUysPdY8xI1OjcCpqtlud6MaAS84NFUsgsYPCTSyJfGKbfN9GAUh+6/zHD81NnjCxlwR791B+HALECFHKT0o41aL2vWCsU2p60bfbzZe26bM0atN48ex+3ZYQ8m6VtFViDP35+DIdoEJwl8DgVEkLKCY2CkpxNs89HJ/cHunNeoZSEjf+vrGs0eDRxxakarc+mqOf77cYE6IdpIyjiwKyHccY+F4HGzYUGbDmFEJmskN9MnpzbU06bPvDEjBEMhZ/CogM4c6GsaeWrln9xTgxEtPsDrrMJTlkX927A74z52bVEhUqo6Ln0IwtW7r5wxv6NPVQt1dHNnQrP0lU5zz5NMk0Bm0Z2keHdfbGmSIHOA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: X-Spam-Checker-Version: SpamAssassin 4.0.1 (2024-03-26) on aws-us-west-2-korg-listserv-alma10-1 On Wed, Oct 21, 2026 at 10:21:53AM +0200, David Hildenbrand (Arm) wrote: > > +1. Did it ever actually work there :) Why not just skip them and > > call it a day :D > > I think QEMU just always sets MADV_MERGABLE and later activates uffd. So that > needs some care to not disable them. So let's rather try to get it fixed properly. > > Can you send out proper patches? Thanks! +1. Lance's direction is right. Unsharing is not an access: do_wp_page() already skips the uffd-wp fault on FAULT_FLAG_UNSHARE, and RWP should do the same. -- Kiryl Shutsemau / Kirill A. Shutemov