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Thu, 05 Mar 2026 03:16:08 -0800 (PST) Date: Thu, 05 Mar 2026 11:16:07 +0000 In-Reply-To: <6206d021-e6c2-4899-b426-cacd71ebd5ef@kernel.org> Mime-Version: 1.0 References: <20260225-page_alloc-unmapped-v1-0-e8808a03cd66@google.com> <6206d021-e6c2-4899-b426-cacd71ebd5ef@kernel.org> X-Mailer: aerc 0.21.0 Message-ID: Subject: Re: [PATCH RFC 00/19] mm: Add __GFP_UNMAPPED From: Brendan Jackman To: "Vlastimil Babka (SUSE)" , Brendan Jackman , Borislav Petkov , Dave Hansen , Peter Zijlstra , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , Wei Xu , Johannes Weiner , Zi Yan Cc: , , , , Sumit Garg , , , Will Deacon , , "Kalyazin, Nikita" , , "Itazuri, Takahiro" , Andy Lutomirski , David Kaplan , Thomas Gleixner , Yosry Ahmed Content-Type: text/plain; charset="UTF-8" X-Rspam-User: X-Rspamd-Server: rspam11 X-Rspamd-Queue-Id: 049671A0018 X-Stat-Signature: 94b66uiyhqo6i4ybu9bu77hgi6kzwbnq X-HE-Tag: 1772709369-910540 X-HE-Meta: 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 Hl1/58PA mur9wCqpZavA9GImC7jzTd0e9FuMJBD6baA6x8L8+3M7V9aJUuOBtb9im5gDOROOTOkCS3nLBXBCPqTS4yWSUAqdsyQU2Aee4FkQ4EJJ8WTaG0qlx8kmmPlVpzQJ6FnctF/1+KOyNlnuQDF36mI1mWt4eaXwG6Rc7POcjAyw+imQMglydrySApF7ouZNpJ7C47mfPBO/dpMv5VZmLGl9pcI4IuuSr4tMwDjkZvSKNLRovmLLixbMH4uj9Us8S0u9SdCXN7q9LYCXq6DIgEyyscMPukwrvmvJDPpYlavyM3b0WMOHcDaato/ZHDsfCUsUQfncU Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hey Vlastimil, sorry for the delay I've been unexpectedly out of office. On Mon Mar 2, 2026 at 3:36 PM UTC, Vlastimil Babka (SUSE) wrote: > On 2/25/26 17:34, Brendan Jackman wrote: >> .:: What? Why? >> .:: Why [RFC]? >> >> I really wanted to stop sending RFC and start sending PATCHes but >> getting this series out has taken months longer than I expected, so it's >> time to get something on the list. The known issues here are: >> >> 1. __GFP_UNMAPPED isn't useful yet until guest_memfd unmapping support >> [0] gets merged. >> >> 2. Apparently while implementing the mm-local region, I totally forgot >> that KPTI existed on 32-bit systems. I expect the 0-day bot to fire a >> failure on that patch. > I don't think you mentioned (at least in the cover letter) the mm resistance > to add new gfp flags due to number of them being uncomfortably close to 32 > already. But I see you've put the new one behind a config. Together with > point 2 I wonder if this is where we can start making some flags and > associated functionality 64-bit only and change gfp_t to unsigned long? Yeah, making __GFP_UNMAPPED 64bit-only would be fine with me. Ultimately the fact that we have KPTI for 32-bit makes it sound like we would also want ASI for 32-bit, so I guess I would still want to add a GFP flag to support that on 32-bit. But that's a pretty futuristic problem, I would say we should focus on __GFP_UNMAPPED in isolation right now. (Just to be clear regarding point 2 - that bug still matters, even if __GFP_UNMAPPED itself is 64-bit only the mm-local region is separate and needs to be correct on 32-bit).