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spf=none smtp.mailfrom=linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=merlin.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:Message-ID:References:In-Reply-To:Subject:To:From: Date:MIME-Version:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=JzLNooes4XWHzS+RUw6PyqEav++LvP3R8rgz4q5cOJk=; b=y8F/yhwho+74uRGckNsTL+zBQ TZgPIePDb6mhVttcw1KHumrfB04B6cTBp+Cb5jAbe/5LlehclIZIjM/kdWo3wHQMi1TooLM0RjmYc a4AWEItQdjCvQzVphizGaD27GLdWOyxBAwHwAYjpWYljfmuB+WJyK/kY0HhJQJE9IEYjYSGr+JhST Qd88uqIvqp+MiUFKtk5ywh4nu76sOtNzfxHYjhQd27TK3Ub2C6HFq934UGyrtpJQvBRJeS0UesloB hmi9rqSh8S4WeP7EUoJsIcJLDHtLxm8MZO1Nxxh+f1rgsivCDFyGnrQJY0JG4MzHmEQALqpwq28XQ 6x8L5p+jQ==; Received: from localhost ([::1] helo=merlin.infradead.org) by merlin.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkNKz-0004cS-4B; Wed, 02 Dec 2020 08:18:09 +0000 Received: from mail.kernel.org ([198.145.29.99]) by merlin.infradead.org with esmtps (Exim 4.92.3 #3 (Red Hat Linux)) id 1kkNKw-0004bd-I4 for linux-arm-kernel@lists.infradead.org; Wed, 02 Dec 2020 08:18:07 +0000 Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8CE08221FA; Wed, 2 Dec 2020 08:18:05 +0000 (UTC) Received: from disco-boy.misterjones.org ([51.254.78.96] helo=www.loen.fr) by disco-boy.misterjones.org with esmtpsa (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_128_GCM_SHA256 (Exim 4.94) (envelope-from ) id 1kkNKt-00FHEK-BO; Wed, 02 Dec 2020 08:18:03 +0000 MIME-Version: 1.0 Date: Wed, 02 Dec 2020 08:18:03 +0000 From: Marc Zyngier To: Will Deacon Subject: Re: [PATCH v4 03/14] KVM: arm64: Kill 32-bit vCPUs on systems with mismatched EL0 support In-Reply-To: <20201201165707.GF27783@willie-the-truck> References: <20201124155039.13804-1-will@kernel.org> <20201124155039.13804-4-will@kernel.org> <9bd06b193e7fb859a1207bb1302b7597@kernel.org> <20201127115304.GB20564@willie-the-truck> <583c4074bbd4cf8b8085037745a5d1c0@kernel.org> <20201127172434.GA984327@google.com> <9de8639549040b4478b312503fd5a23f@kernel.org> <20201201165707.GF27783@willie-the-truck> User-Agent: Roundcube Webmail/1.4.9 Message-ID: <5e59a8f5bc84403ce2c8f26aa874cb1b@kernel.org> X-Sender: maz@kernel.org X-SA-Exim-Connect-IP: 51.254.78.96 X-SA-Exim-Rcpt-To: will@kernel.org, qperret@google.com, linux-arm-kernel@lists.infradead.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, catalin.marinas@arm.com, gregkh@linuxfoundation.org, peterz@infradead.org, morten.rasmussen@arm.com, qais.yousef@arm.com, surenb@google.com, tj@kernel.org, lizefan@huawei.com, hannes@cmpxchg.org, mingo@redhat.com, juri.lelli@redhat.com, vincent.guittot@linaro.org, kernel-team@android.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201202_031806_758061_37CE1065 X-CRM114-Status: GOOD ( 20.26 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Juri Lelli , kernel-team@android.com, Vincent Guittot , Quentin Perret , Peter Zijlstra , Catalin Marinas , Johannes Weiner , linux-kernel@vger.kernel.org, Qais Yousef , Ingo Molnar , Li Zefan , Greg Kroah-Hartman , Tejun Heo , Suren Baghdasaryan , Morten Rasmussen , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 2020-12-01 16:57, Will Deacon wrote: > On Fri, Nov 27, 2020 at 06:16:35PM +0000, Marc Zyngier wrote: >> On 2020-11-27 17:24, Quentin Perret wrote: >> > On Friday 27 Nov 2020 at 17:14:11 (+0000), Marc Zyngier wrote: >> >> [...] >> >> > > Yeah, the sanitized read feels better, if only because that is >> > > what we are going to read in all the valid cases, unfortunately. >> > > read_sanitised_ftr_reg() is sadly not designed to be called on >> > > a fast path, meaning that 32bit guests will do a bsearch() on >> > > the ID-regs every time they exit... >> > > >> > > I guess we will have to evaluate how much we loose with this. >> > >> > Could we use the trick we have for arm64_ftr_reg_ctrel0 to speed this >> > up? >> >> Maybe. I want to first verify whether this has any measurable impact. >> Another possibility would be to cache the last >> read_sanitised_ftr_reg() >> access, just to see if that helps. There shouldn't be that many code >> paths hammering it. > > We don't have huge numbers of ID registers, so the bsearch shouldn't be > too expensive. However, I'd like to remind myself why we can't index > into > the feature register array directly as we _should_ know all of this > stuff > at compile time, right? Simply because it's not indexed by ID reg. It's just an ordered collection, similar to the for sys_reg emulation in KVM. You can compute the index ahead of time, but just not at compile time. At least not with the way the arm64_ftr_regs array is built. M. -- Jazz is not dead. It just smells funny... _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel