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[35.190.207.78]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-499c33098besm53780005e9.0.2026.08.23.09.52.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 23 Aug 2026 09:52:50 -0700 (PDT) Date: Sun, 23 Aug 2026 16:52:47 +0000 From: Adrian =?utf-8?Q?Barna=C5=9B?= To: Ard Biesheuvel Cc: linux-kernel@vger.kernel.org, Ard Biesheuvel , Catalin Marinas , Will Deacon , Steven Rostedt , Masami Hiramatsu , Mark Rutland , Andrew Morton , Mike Rapoport , Luis Chamberlain , Petr Pavlu , Daniel Gomez , Sami Tolvanen , Aaron Tomlin , Ryan Roberts , Kevin Brodsky , linux-arm-kernel@lists.infradead.org, linux-trace-kernel@vger.kernel.org, linux-mm@kvack.org, linux-modules@vger.kernel.org Subject: Re: [RFC PATCH 5/9] arm64: mm: Permit permissions changes on huge vmappings Message-ID: References: <20260822135323.795946-11-ardb+git@google.com> <20260822135323.795946-16-ardb+git@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <20260822135323.795946-16-ardb+git@google.com> X-Rspam-User: X-Stat-Signature: b616qzmgfiwxgq13ezdnnrrrbbuqcb4o X-Rspamd-Server: rspam09 X-Rspamd-Queue-Id: 5F4B640005 X-HE-Tag: 1787503973-639756 X-HE-Meta: U2FsdGVkX18dt5Xr9n2R4r/pLHjyZbSmJ/2OI6y1TsFMTUQPMQQkMRMVOWoKfN/7vgxN0pH1o41F67cNCkk/7gfqSX5KYaRgbnMWyOu2BvihKj3oy+Afu3z4UdJekjFKCgUbFTN/nM2RYBsMrivHoBr7IhemIjcXJ9Pkfy7xfjLBi5qc0Tk45EWp06sVXdCl3XQyRITpXQWh9THE4muUmnoNeZXRBK8zvUejhkHZgrsLuQBnnWdM3DY6PX3klPnEep3BjpMylbyo03mgNFwn700Q9z30Tf2kpFHg/UQaqWDB0BpRkh2zdOy+7oI7p2pr1ZhfmPBa/nVer3W9LUAlPrQLTc/eeM6YEd8CzxdUmFYRjOe8amIziPnLsv9C3DGOCMHmHopBsH0ZjRtPaNH7qoF4nkw5P5Kn/kB8Cd5z74xDg6iR3jMp7enDdDArnecFrHTBgHMESoAoqNK+fAfJwdmpAb8flJBiachrEyag+VfhER6U7J9/HvT/CGKJQf9rKD4rZ/ZTniXLYmiM4a4mUG9F30THt74OF+auneB5iT3R85QhivxWdrdOj2EgJktGiutQLoOD3N/SkezWZt0vhHovcmU0fK0UzVJuRzQRgv1Ir8SZt33AGFuVAnBWT4qzXvnBNwkf9ZJwreOlTZTV97q9aqSH3MPuQ64IlNt1eKZzfrVyX2E0qSidFiPSQb7rNHqjuxLBZH0rN+VT2TQFzYfk4JTLtWPqB5LfD5xMjVhv8iaHq+7b3UMz/WF3mlJVlkF3hG5gff3Nfc4tV60fzkzbon+/r/FvB3QZeXu/2xcaB+x4yqM4ACPgbvK7+SYgkNEBV3MCcWZqnC12Jvqjk8QBH4xxMc4cjbR0av6ramfHKLD/qEBb+QHYPzfJhfebX6QXMIVxtyhchrkZZD2k0a9KnRBOqMN3UvoYd6c/1zUy2xuJWGI/c0gYDWSpaSRgkeCzums+PUvDuYG+t5W fG2nQOId 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 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: Hi Ard On Sat, Aug 22, 2026 at 03:53:27PM +0200, Ard Biesheuvel wrote: >From: Ard Biesheuvel > >Allow permission changes on huge vmappings in cases where no splitting >is needed (i.e., the region is aligned sufficiently), or when the system >has support for splitting live mappings. > >Signed-off-by: Ard Biesheuvel >--- > arch/arm64/mm/pageattr.c | 13 ++++++++++--- > 1 file changed, 10 insertions(+), 3 deletions(-) > >diff --git a/arch/arm64/mm/pageattr.c b/arch/arm64/mm/pageattr.c >index bbe98ac9ad8c..20ff9cb273c1 100644 >--- a/arch/arm64/mm/pageattr.c >+++ b/arch/arm64/mm/pageattr.c >@@ -169,8 +169,6 @@ static int change_memory_common(unsigned long addr, int numpages, > * we are operating on does not result in such splitting. > * > * Let's restrict ourselves to mappings created by vmalloc (or vmap). >- * Disallow VM_ALLOW_HUGE_VMAP mappings to guarantee that only page >- * mappings are updated and splitting is never needed. > * > * So check whether the [addr, addr + size) interval is entirely > * covered by precisely one VM area that has the VM_ALLOC flag set. >@@ -179,7 +177,16 @@ static int change_memory_common(unsigned long addr, int numpages, > if (!area || > ((unsigned long)kasan_reset_tag((void *)end) > > (unsigned long)kasan_reset_tag(area->addr) + area->size) || >- ((area->flags & (VM_ALLOC | VM_ALLOW_HUGE_VMAP)) != VM_ALLOC)) >+ !(area->flags & VM_ALLOC)) >+ return -EINVAL; >+ >+ /* >+ * Disallow VM_ALLOW_HUGE_VMAP mappings unless the region is PMD >+ * aligned, or splitting live huge mappings is supported. >+ */ >+ if ((area->flags & VM_ALLOW_HUGE_VMAP) && >+ ((start % PMD_SIZE) || (size % PMD_SIZE)) && If I understand the intention here correctly, I don't think it is valid. Even if it is PMD-sized and PMD-aligned, it would still cause a split because the loop below is not using page order, but performs attribute changes page by page. Best regards, Adrian