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=-5.5 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 B0EAAC4338F for ; Fri, 23 Jul 2021 15:49:52 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 31A3E60EB6 for ; Fri, 23 Jul 2021 15:49:52 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 31A3E60EB6 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id A303A4B162; Fri, 23 Jul 2021 11:49:51 -0400 (EDT) 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 wmxJKi6TBXk5; Fri, 23 Jul 2021 11:49:49 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 919664B14F; Fri, 23 Jul 2021 11:49:49 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id A45EA4B14C for ; Fri, 23 Jul 2021 11:49:48 -0400 (EDT) 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 H+XXTuiLjCeP for ; Fri, 23 Jul 2021 11:49:47 -0400 (EDT) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 5DB2C4B0FC for ; Fri, 23 Jul 2021 11:49:47 -0400 (EDT) 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 D4649139F; Fri, 23 Jul 2021 08:49:46 -0700 (PDT) Received: from [10.57.8.76] (unknown [10.57.8.76]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 0262A3F73D; Fri, 23 Jul 2021 08:49:44 -0700 (PDT) Subject: Re: [PATCH v2 3/3] kvm/arm: Align the VMID allocation with the arm64 ASID one To: Will Deacon References: <20210616155606.2806-1-shameerali.kolothum.thodi@huawei.com> <20210616155606.2806-4-shameerali.kolothum.thodi@huawei.com> <20210721163138.GD11003@willie-the-truck> <20210722095010.GA12012@willie-the-truck> <43b32e77-52b1-8524-63a1-c99578c2dd1d@arm.com> <20210722153814.GA12566@willie-the-truck> From: Vladimir Murzin Message-ID: <53f9359d-d3ac-5a3c-1e29-9fb7e9fda22c@arm.com> Date: Fri, 23 Jul 2021 16:49:46 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0 MIME-Version: 1.0 In-Reply-To: <20210722153814.GA12566@willie-the-truck> Content-Language: en-US Cc: "jean-philippe@linaro.org" , "catalin.marinas@arm.com" , Linuxarm , "linux-kernel@vger.kernel.org" , "maz@kernel.org" , "kvmarm@lists.cs.columbia.edu" , "linux-arm-kernel@lists.infradead.org" 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 Will, On 7/22/21 4:38 PM, Will Deacon wrote: > Hi Vladimir, > > On Thu, Jul 22, 2021 at 04:22:26PM +0100, Vladimir Murzin wrote: >> On 7/22/21 10:50 AM, Will Deacon wrote: >>> As an aside: I'm more and more inclined to rip out the CnP stuff given >>> that it doesn't appear to being any benefits, but does have some clear >>> downsides. Perhaps something for next week. >> >> Can you please clarify what do you mean by "it doesn't appear to being any >> benefits"? IIRC, Cortex-A65 implements CnP hint and I've heard that some >> payloads seen improvement... > > Has anybody taped that out? I'd have thought building an SMT design in 2021 > is a reasonably courageous thing to do. As you said three can be niche for that... > > The issue I'm getting at is that modern cores seem to advertise CnP even > if they ignore it internally, maybe because of some big/little worries? Should we employ CPU errata framework for such cores to demote CnP? > That would be fine if it didn't introduce complexity and overhead to the > kernel, but it does and therefore I think we should rip it out (or at > least stick it behind a "default n" config option if there are some niche > users). "default n" still better then no code at all :) Cheers Vladimir > > There are also open questions as to exactly what CnP does because the > architecture is not clear at all (for example TTBRx_EL1.CnP is permitted > to be cached in a TLB). > > CHeers, > > Will > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm