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a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1677142991; bh=A6FgptrrYUoOz1tvlLQnDnjqNkLOWOvmXcwfXX55TRM=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=Sxh03O33j2ejJ4jpoNj45YBc0t3nTQjBMx6/t1CIuoWEq6bq6RJ5MbkMXBaziU7XB jBiG0NPfBzCsygzhwl7U70Ww5RfkjSnt+X2BTV6rjwgAaGTiYqUcba9/0pT+io/mCD qZjDVFRaRc9HIBivB+ue1JGVXAtvvm1UbhzqMGcLED1yhWHHCkwegOuY4HGxgzRiCg f0Bo1SH/aireTElW18d3BAsiBz7JJnD51MrXyy0cHzXaSpbqcVGW4LFW+QXo/O27ev dYaWcQfX+BrgYmW9lN4LpflDeWLq0Uvns/HwiYnDQcTdPzrAi97W/g4IH1TOpboAVX U2MKuHMptf1ug== Received: from sofa.misterjones.org ([185.219.108.64] helo=goblin-girl.misterjones.org) by disco-boy.misterjones.org with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.95) (envelope-from ) id 1pV7VM-00CaNM-TI; Thu, 23 Feb 2023 09:03:08 +0000 Date: Thu, 23 Feb 2023 09:03:08 +0000 Message-ID: <86a614ycs3.wl-maz@kernel.org> From: Marc Zyngier To: Yu Zhao Cc: Will Deacon , Jonathan Corbet , Michael Larabel , kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-mm@google.com, Andrew Morton , Paolo Bonzini Subject: Re: [PATCH mm-unstable v1 3/5] kvm/arm64: add kvm_arch_test_clear_young() In-Reply-To: References: <20230217041230.2417228-1-yuzhao@google.com> <20230217041230.2417228-4-yuzhao@google.com> <86lekwy8d7.wl-maz@kernel.org> User-Agent: Wanderlust/2.15.9 (Almost Unreal) SEMI-EPG/1.14.7 (Harue) FLIM-LB/1.14.9 (=?UTF-8?B?R29qxY0=?=) APEL-LB/10.8 EasyPG/1.0.0 Emacs/28.2 (aarch64-unknown-linux-gnu) MULE/6.0 (HANACHIRUSATO) MIME-Version: 1.0 (generated by SEMI-EPG 1.14.7 - "Harue") Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable X-SA-Exim-Connect-IP: 185.219.108.64 X-SA-Exim-Rcpt-To: yuzhao@google.com, will@kernel.org, corbet@lwn.net, michael@michaellarabel.com, kvmarm@lists.linux.dev, kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, linuxppc-dev@lists.ozlabs.org, x86@kernel.org, linux-mm@google.com, akpm@linux-foundation.org, pbonzini@redhat.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-Rspam-User: X-Rspamd-Queue-Id: 01E148000E X-Rspamd-Server: rspam01 X-Stat-Signature: ia934qsk5ptpwmons1x4uwagu7wc9h73 X-HE-Tag: 1677142992-787283 X-HE-Meta: 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 AZPGgCCI d+5sAKilVLRGTbhDQyTS24Q9jMAmwnB6wO9gDI/9TgzpFU7pG1KoX9E4z4K3hGPzJNlpIs9gwWNc8jHoC0VUNSm0j1VphQGM2S7ns/TiDjvUoSmJDpdX+a20z1Su/xFbBfwQ2BjOHfgkJ+8IbMz8V/tVl6UPFaeJqSa9Bh79YYQieaPwQbTg1WPLqpQpk42ZcXN52MFHu8tiL1wA6YXnlVQVd7f19IbykzVK7RvdIGeZ2mWoDabwBcQfDZ39UoTkmvo9Pd2mNnR0muxSORHld2PuIbPDlxtBotjikv2siNctnBv20lA8zlC2MV2fUcvBhj94QcpdMcSfjLyJB1HPZmzBPIvv8p049rNu2sKwpHt3heu2noVGYDZcxJDwhJwiZGGRdH1oA/1+niSYOxZ0lhbkicM78cIMp4FikWjDbNRV4nl2z60Ik7UPbPA== 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: On Thu, 23 Feb 2023 03:58:47 +0000, Yu Zhao wrote: >=20 > On Fri, Feb 17, 2023 at 2:00=E2=80=AFAM Marc Zyngier wro= te: > > > > On Fri, 17 Feb 2023 04:21:28 +0000, > > Yu Zhao wrote: > > > > > > On Thu, Feb 16, 2023 at 9:12 PM Yu Zhao wrote: > > > > > > > > This patch adds kvm_arch_test_clear_young() for the vast majority of > > > > VMs that are not pKVM and run on hardware that sets the accessed bit > > > > in KVM page tables. > > > > I'm really interested in how you can back this statement. 90% of the > > HW I have access to is not FEAT_HWAFDB capable, either because it > > predates the feature or because the feature is too buggy to be useful. >=20 > This is my expericen too -- most devices are pre v8.2. And yet you have no issue writing the above. Puzzling. >=20 > > Do you have numbers? >=20 > Let's do a quick market survey by segment. The following only applies > to ARM CPUs: >=20 > 1. Phones: none of the major Android phone vendors sell phones running > VMs; no other major Linux phone vendors. Maybe you should have a reality check and look at what your own employer is shipping. > 2. Laptops: only a very limited number of Chromebooks run VMs, namely > ACRVM. No other major Linux laptop vendors. Again, your employer disagree. > 3. Desktops: no major Linux desktop vendors. My desktop disagree (I send this from my arm64 desktop VM ). > 4. Embedded/IoT/Router: no major Linux vendors run VMs (Android Auto > can be a VM guest on QNX host). This email is brought to you via a router VM on an arm64 box. > 5. Cloud: this is where the vast majority VMs come from. Among the > vendors available to the general public, Ampere is the biggest player. > Here [1] is a list of its customers. The A-bit works well even on its > EVT products (Neoverse cores). Just the phone stuff dwarfs the number of cloud hosts. Hopefully your patches are better than your market analysis... M. --=20 Without deviation from the norm, progress is not possible.