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b=WeNxs0kkEZTOSayX6k8SqjOWRMZrokZFwAHLQyFciN4Akkj37P02YgRmGi/jEKLQj OZ0JYqIWL3JODmbUhux7WPSTUPcgacvDpAhSrr8wVADnrRFQGOqTqg3nx7XKyPHB9Q wu6rHrJ/QkV0/n2rY9vKmcSABJEnEtBQ8Hy4VFaiXW9676QLCF+cgANsS4/OsRJIoP KHdjEctL7UQo2970NOWNI2mjch6/U0a5wic2XoLpqSWdJqDp2Lv71i3F+ceG5+kpJA XgWKlt7GFvydVEizWjUz+9Dd6ED15kZ8IYhOu7xToyH2GIwIMt+mP2639Zpp6UHikV 3zYAFhvKwMxrw== Message-ID: <42a5cd12-9569-4719-bd6e-95dc0100c065@kernel.org> Date: Thu, 9 Jul 2026 11:58:03 +0200 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 00/18] Another attempt at HVO support on arm64 To: James Houghton , Will Deacon , Catalin Marinas , Muchun Song , Oscar Salvador Cc: Nikos Nikoleris , Linu Cherian , Mark Rutland , Andrew Morton , Ryan Roberts , Nanyong Sun , Yu Zhao , Frank van der Linden , David Rientjes , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org References: <20260708031129.3503195-1-jthoughton@google.com> From: "David Hildenbrand (Arm)" Content-Language: en-US Autocrypt: addr=david@kernel.org; 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charset=UTF-8 Content-Transfer-Encoding: 7bit X-Rspamd-Server: rspam06 X-Rspamd-Queue-Id: 888D1C0002 X-Stat-Signature: 41hkn7c3hrfdq9gmbqzgf3uwh6nekcui X-Rspam-User: X-HE-Tag: 1783591090-668894 X-HE-Meta: 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 /OvBlG3a t3GnH/1DsSq6t+yld6AvUqqlV27OO6MXiCfoshIgyKaX7Z4KNH7NvMf+VAHJBWWsQfABQIGIiBkPH8NGDQkK/eSFp5fT5WzwcLBNRn9wOS0gnC7sisX/4vxCKPIrny92BOroVwYiiCFQMsp6M3HVrN353hCbAGLMlPKTEqOA+Y+/7YKUgSNfyQ7ExVatM7vbMK2MMLGkkt9+NG1tKQE/rjNsSoecObc0GXSHCmc4zg8sB4mUUh5a5Do/hGCyxEXxkvHogOIj7VvcSt7kZsYm0k6N5gKlafVhHxS0t Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: > -- The AF trick -- > > The trick is that translations with the AF unset cannot be cached in the > TLB (see Rule R_DWZCQ in the Arm ARM), so they can be atomically updated > without needing a full break-before-make sequence. > > So the PTE update sequence becomes: > 1. Atomically clear the AF on the existing PTE. > 2. Invalidate the TLB. > 3. cmpxchg the AF=0 PTE with the new PTE. If this fails, goto 1. > > If there is a CPU on the system that does not support hardware access > flag updates, clearing the AF is problematic, as those CPUs might fault > on the vmemmap usage. Therefore, HVO compatbility checks all CPUs for HW > AF updates. Pretty nice trick, I hope this will fly :) -- Cheers, David