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From: Oliver Upton To: Yu Zhao Cc: James Houghton , Andrew Morton , Paolo Bonzini , David Matlack , Marc Zyngier , Sean Christopherson , Jonathan Corbet , James Morse , Suzuki K Poulose , Zenghui Yu , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , "H. Peter Anvin" , Steven Rostedt , Masami Hiramatsu , Mathieu Desnoyers , Shaoqin Huang , Gavin Shan , Ricardo Koller , Raghavendra Rao Ananta , Ryan Roberts , David Rientjes , Axel Rasmussen , linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-mm@kvack.org, linux-trace-kernel@vger.kernel.org Subject: Re: [PATCH v3 6/7] KVM: arm64: Participate in bitmap-based PTE aging Message-ID: References: <20240401232946.1837665-1-jthoughton@google.com> <20240401232946.1837665-7-jthoughton@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Migadu-Flow: FLOW_OUT X-Rspamd-Queue-Id: 4F8B61C0022 X-Rspam-User: X-Rspamd-Server: rspam04 X-Stat-Signature: 7mt136edyzfknkktydw9jr45ishyxzon X-HE-Tag: 1712041235-84461 X-HE-Meta: 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 oHBCZc0G 4drA/xmwRbVv+WP6oyqiR12N5vFH9GicPRwYRBAbhZ9/y9I13Sax53LD7DkTviS8eI0OZSnxfKuoLmNSgRu0rgn5v28Ro0C+Y5fDjy88ug7PQCWGrkkOwJ7w9CdTUPCyXIEBXyzU5va4KHVo= X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Tue, Apr 02, 2024 at 12:06:56AM -0400, Yu Zhao wrote: > On Mon, Apr 1, 2024 at 7:30 PM James Houghton wrote: > > Suggested-by: Yu Zhao > > Thanks but I did not suggest this. Entirely up to you, but I would still want to credit everyone who contributed to a feature even if the underlying implementation has changed since the original attempt. > What I have in v2 is RCU based. I hope Oliver or someone else can help > make that work. Why? If there's data to show that RCU has a material benefit over taking the MMU lock for read then I'm all for it. Otherwise, the work required to support page-table walkers entirely outside of the MMU lock isn't justified. In addition to ensuring that page table teardown is always RCU-safe, we'd need to make sure all of the walkers that take the write lock are prepared to handle races. > Otherwise we can just drop this for now and revisit > later. I really wouldn't get hung up on the locking as the make-or-break for whether arm64 supports this MMU notifier. -- Thanks, Oliver