From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7F38CC63697 for ; Thu, 19 Nov 2020 16:58:30 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id CDF8E24655 for ; Thu, 19 Nov 2020 16:58:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CDF8E24655 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 52D2B4B564; Thu, 19 Nov 2020 11:58:29 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id Gkc89xT+ddtL; Thu, 19 Nov 2020 11:58:28 -0500 (EST) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 368664B4FD; Thu, 19 Nov 2020 11:58:28 -0500 (EST) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 730D14B488 for ; Thu, 19 Nov 2020 11:58:26 -0500 (EST) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id fhzz9nN0cV7w for ; Thu, 19 Nov 2020 11:58:25 -0500 (EST) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 317874B4B3 for ; Thu, 19 Nov 2020 11:58:25 -0500 (EST) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id D5D0A1595; Thu, 19 Nov 2020 08:58:24 -0800 (PST) Received: from [192.168.2.21] (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id AFC743F718; Thu, 19 Nov 2020 08:58:23 -0800 (PST) From: James Morse Subject: Re: [RFC PATCH v3 04/16] arm64: Introduce CPU SPE feature To: Alexandru Elisei References: <20201027172705.15181-1-alexandru.elisei@arm.com> <20201027172705.15181-5-alexandru.elisei@arm.com> Message-ID: <418e3bf6-159c-6d1f-2b84-2fdb10c3cddd@arm.com> Date: Thu, 19 Nov 2020 16:58:22 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: <20201027172705.15181-5-alexandru.elisei@arm.com> Content-Language: en-GB Cc: maz@kernel.org, linux-arm-kernel@lists.infradead.org, will@kernel.org, kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu Hi Alex, On 27/10/2020 17:26, Alexandru Elisei wrote: > Detect Statistical Profiling Extension (SPE) support using the cpufeatures > framework. The presence of SPE is reported via the ARM64_SPE capability. > > The feature will be necessary for emulating SPE in KVM, because KVM needs > that all CPUs have SPE hardware to avoid scheduling a VCPU on a CPU without > support. For this reason, the feature type ARM64_CPUCAP_SYSTEM_FEATURE has > been selected to disallow hotplugging a CPU which doesn't support SPE. Can you mention the existing driver in the commit message? Surprisingly it doesn't use cpufeature at all. It looks like arm_spe_pmu_dev_init() goes out of its way to support mismatched systems. (otherwise the significance of the new behaviour isn't clear!) I read it as: the host is fine with mismatched systems, and the existing drivers supports this. But KVM is not. After this patch you can't make the system mismatched 'late'. Thanks, James _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm