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Thu, 3 Sep 2026 07:27:03 +0000 (UTC) X-Farcaster-Flow-ID: 31c43739-7d7e-4b18-a143-798b81c75300 Received: from EX19D001UWA001.ant.amazon.com (10.13.138.214) by EX19MTAUWA001.ant.amazon.com (10.250.64.218) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.45; Thu, 3 Sep 2026 07:27:03 +0000 Received: from b0f1d8753182.ant.amazon.com (10.106.83.23) by EX19D001UWA001.ant.amazon.com (10.13.138.214) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_128_CBC_SHA) id 15.2.2562.46; Thu, 3 Sep 2026 07:26:57 +0000 From: Takahiro Itazuri To: Yosry Ahmed , Sean Christopherson , Brendan Jackman CC: Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , "David Hildenbrand" , Vlastimil Babka , "Mike Rapoport" , Wei Xu , Johannes Weiner , Zi Yan , Lorenzo Stoakes , , , , Sumit Garg , Will Deacon , , Roy Patrick , Andy Lutomirski , David Kaplan , Thomas Gleixner , Patrick Bellasi , Reiji Watanabe , Nikita Kalyazin , Ackerley Tng , "Takahiro Itazuri" , Subject: Re: [PATCH v3 03/26] mm: introduce AS_NO_DIRECT_MAP Date: Thu, 3 Sep 2026 08:26:26 +0100 Message-ID: <20260903072625.62694-2-itazur@amazon.com> X-Mailer: git-send-email 2.43.1 In-Reply-To: References: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain X-Originating-IP: [10.106.83.23] X-ClientProxiedBy: EX19D032UWB004.ant.amazon.com (10.13.139.136) To EX19D001UWA001.ant.amazon.com (10.13.138.214) X-Rspam-User: X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: 9CEF3180007 X-Stat-Signature: nwiad16en7yfjnhgywgr1kw3nqu71axy X-HE-Tag: 1788420427-383399 X-HE-Meta: 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 whA3l/ER 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Some of you on the KVM side already know this, but for those on the MM side who may not, I am taking over the guest_memfd direct-map removal series. I have finally caught up with this thread, and I sincerely apologize for joining so late; other commitments kept me from catching up sooner. On Fri, 7 Aug 2026 15:48:24 -0700, Yosry Ahmed wrote: > > I'm not ok punting on that, i.e. whatever we come up with needs to land= alongside > > AS_NO_DIRECT_MAP, or at least before guest_memfd tries to use AS_NO_DIR= ECT_MAP. > > Yup, I meant the latter. > > > The only way KVM can use AS_NO_DIRECT_MAP without GUP is with a massive= list of > > caveats and addendums on things the VMM and guest can't do. I'm not ok= merging > > guest_memfd support for AS_NO_DIRECT_MAP with such a list. > > This series is not adding the support in guest_memfd, just adding the > generic AS_NO_DIRECT_MAP and using it for secretmem. Followup work is > needed to plumb it for guest_memfd anyway, and I am proposing that we > also punt the GUP story to that (when we have an actual user). My reading of the discussion is that the generic AS_NO_DIRECT_MAP support can land with GUP rejecting such mappings, provided that a generic GUP-like access mechanism is in place before guest_memfd starts using AS_NO_DIRECT_MAP. As far as I know, Brendan is no longer at Google. I do not know whether he plans to continue the ALLOC_UNMAPPED / mermap work, or whether someone else at Google has taken it over. If that work is not already underway, I would like to respin the AS_NO_DIRECT_MAP introduction and secretmem adoption as a standalone MM series, separate from ALLOC_UNMAPPED and mermap. The AS_NO_DIRECT_MAP changes originated in the guest_memfd direct-map removal series, and splitting the MM and KVM parts was already requested during review. The proposed MM series would include: - the folio direct-map helpers; - the AS_NO_DIRECT_MAP flag and filemap lifecycle; - the current GUP and build-ID rejections, while keeping the mlock check specific to secretmem; and - the secretmem conversion. I would leave ALLOC_UNMAPPED, freetypes, mermap, the allocator fast path, and the KVM / guest_memfd integration out of that series. This would not change the requirement discussed by Sean and Yosry above: the GUP-like access problem would still need to be resolved before enabling AS_NO_DIRECT_MAP for guest_memfd. Please let me know if this work is already being continued; if not, does the standalone MM series described above sound reasonable? Thanks, Takahiro