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Wed, 22 Apr 2026 05:27:03 -0400 (EDT) Date: Wed, 22 Apr 2026 10:27:02 +0100 From: Kiryl Shutsemau To: "David Hildenbrand (Arm)" Cc: Andrew Morton , Peter Xu , Lorenzo Stoakes , Mike Rapoport , Suren Baghdasaryan , Vlastimil Babka , "Liam R . Howlett" , Zi Yan , Jonathan Corbet , Shuah Khan , Sean Christopherson , Paolo Bonzini , linux-mm@kvack.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-kselftest@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC, PATCH 00/12] userfaultfd: working set tracking for VM guest memory Message-ID: References: <55019037-4f1c-4d9c-83ee-3a844d8f3d5e@kernel.org> <1a499781-1115-44bc-adbf-2ac3769354ca@kernel.org> <4c635703-3d8d-4cfa-bb98-7f6f5fcbe547@kernel.org> <34f75083-29a3-4860-8a6e-94551d37ac6a@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Stat-Signature: mbhg5p33pyeanhcgwcn7w9x674b7piwa X-Rspam-User: X-Rspamd-Server: rspam02 X-Rspamd-Queue-Id: EE1AFC000C X-HE-Tag: 1776850026-826934 X-HE-Meta: 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 RBU67ADT FiT2GYjMe0Xu13gJ4EbHa/+/XHCW4EMnulQ59Z7qg5AIaWny4NNHUQ2VBK3WgbkQq0QDB9MY8QBrCpV0sXS/dWIno+M/md23ZCUyadjec6540tYO/pnbamdta6+jBMSDRL99Ed3CulFCKq1oxEHqiauZ5EcrxJJVW0Q590gxlMROmv6p9QYIZg5IqYpyxTyWId7GvSpXM6Ydr7hiKD6cWi20nIwF8sMd8efF9XFSC4KQvGQ/43HNp0+uXVA== Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 21, 2026 at 03:33:27PM +0100, Kiryl Shutsemau wrote: > > 3) Some other stuff needs a second thought, like > > > > diff --git a/mm/gup.c b/mm/gup.c > > index 8e7dc2c6ee738..08fc18f1290d4 100644 > > --- a/mm/gup.c > > +++ b/mm/gup.c > > @@ -695,7 +695,8 @@ static inline bool can_follow_write_pmd(pmd_t pmd, struct page *page, > > /* ... and a write-fault isn't required for other reasons. */ > > if (pmd_needs_soft_dirty_wp(vma, pmd)) > > return false; > > - return !userfaultfd_huge_pmd_wp(vma, pmd); > > + return !userfaultfd_huge_pmd_wp(vma, pmd) && > > + !userfaultfd_huge_pmd_rwp(vma, pmd); > > } > > > > How can a pte be writable and prot_none at the same time? Maybe just confused AI > > output that you should carefully double check before sending that out officially. > > Note that this path is for !pmd_write() case to begin with. It serves > FOLL_FORCE case. I believe this check is correct: we don't want to allow > to write to such pages even with FOLL_FORCE. > > But looking around, I missed gup_can_follow_protnone() modification. It > has to return false for RWP. With gup_can_follow_protnone() fixed, the checks in can_follow_write_pmd/pte() are redundant. Will drop them. -- Kiryl Shutsemau / Kirill A. Shutemov