From mboxrd@z Thu Jan 1 00:00:00 1970 From: Julien Grall Subject: Re: [PATCH 06/14] KVM: arm/arm64: Factor out VMID into struct kvm_vmid Date: Fri, 22 Feb 2019 11:42:46 +0000 Message-ID: <44bd2df6-8011-c77f-a83a-95c3529287c0@arm.com> References: <20190124140032.8588-1-christoffer.dall@arm.com> <20190124140032.8588-7-christoffer.dall@arm.com> <1978ee57-c7bd-e55a-4e77-ad0b4b62d1d1@arm.com> <20190222091848.21f7f8e6@why.wild-wind.fr.eu.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Cc: "kvm@vger.kernel.org" , nd , Christoffer Dall , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" To: Marc Zyngier Return-path: In-Reply-To: <20190222091848.21f7f8e6@why.wild-wind.fr.eu.org> Content-Language: en-US List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org List-Id: kvm.vger.kernel.org Hi Marc, On 22/02/2019 09:18, Marc Zyngier wrote: > On Thu, 21 Feb 2019 11:02:56 +0000 > Julien Grall wrote: > > Hi Julien, > >> Hi Christoffer, >> >> On 24/01/2019 14:00, Christoffer Dall wrote: >>> Note that to avoid mapping the kvm_vmid_bits variable into hyp, we >>> simply forego the masking of the vmid value in kvm_get_vttbr and rely on >>> update_vmid to always assign a valid vmid value (within the supported >>> range). >> >> [...] >> >>> - kvm->arch.vmid = kvm_next_vmid; >>> + vmid->vmid = kvm_next_vmid; >>> kvm_next_vmid++; >>> - kvm_next_vmid &= (1 << kvm_vmid_bits) - 1; >>> - >>> - /* update vttbr to be used with the new vmid */ >>> - pgd_phys = virt_to_phys(kvm->arch.pgd); >>> - BUG_ON(pgd_phys & ~kvm_vttbr_baddr_mask(kvm)); >>> - vmid = ((u64)(kvm->arch.vmid) << VTTBR_VMID_SHIFT) & VTTBR_VMID_MASK(kvm_vmid_bits); >>> - kvm->arch.vttbr = kvm_phys_to_vttbr(pgd_phys) | vmid | cnp; >>> + kvm_next_vmid &= (1 << kvm_get_vmid_bits()) - 1; >> >> The arm64 version of kvm_get_vmid_bits does not look cheap. Indeed it required >> to read the sanitized value of SYS_ID_AA64MMFR1_EL1 that is implemented using >> the function bsearch. >> >> So wouldn't it be better to keep kvm_vmid_bits variable for use in update_vttbr()? > > How often does this happen? Can you measure this overhead at all? > > My understanding is that we hit this path on rollover only, having IPIed > all CPUs and invalidated all TLBs. I seriously doubt you can observe > any sort of overhead at all, given that it is so incredibly rare. But > feel free to prove me wrong! That would happen on roll-over and the first time you allocate VMID for the VM. I am planning to run some test with 3-bit VMIDs and provide them next week. Cheers, -- Julien Grall 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=-1.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, URIBL_BLOCKED autolearn=ham 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 306B9C43381 for ; Fri, 22 Feb 2019 11:42:56 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 00AF52075B for ; Fri, 22 Feb 2019 11:42:55 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="suIDCgC5" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 00AF52075B Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-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=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=9KfVYyGmzGLuUmQf35K+uwwzS7D8NwzoYN68jqBuBA8=; b=suIDCgC5wxMVy0z4wGsnXrZST GAoBadI1sKrSYRuJLsmqRntTF0AKV/2dkv16mup3VS5YPoAPbH+9+e3A3fYI3iTAAoh4rRG+KdNmX vUGP3s9gGRXmcMz/0wp7PT0jpZf+JP8ubC6WQiC1SfNslcvLBvragCh6N0PS8AlEDahFdrnZcsvAD /S0ovesO4ZKa9DpYQSyWPs7OXCkXvvE27ryAk60OXFg7gstmBwtpORCpbtacpQ1ktwcagAKuowdkr cI5dCla9OUWSBjOlqLPSStpw5GXO+dGACx1dQTtDcHqKsa4YsFAxhRd1cpTn4Inz4vfyXxXItLYYx VTPxQ/iKA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gx9EC-0006eq-KL; Fri, 22 Feb 2019 11:42:52 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1gx9E9-0006eJ-Dr for linux-arm-kernel@lists.infradead.org; Fri, 22 Feb 2019 11:42:50 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id ECFD715AB; Fri, 22 Feb 2019 03:42:48 -0800 (PST) Received: from [10.1.196.50] (e108454-lin.cambridge.arm.com [10.1.196.50]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id D8A953F5C1; Fri, 22 Feb 2019 03:42:47 -0800 (PST) Subject: Re: [PATCH 06/14] KVM: arm/arm64: Factor out VMID into struct kvm_vmid To: Marc Zyngier References: <20190124140032.8588-1-christoffer.dall@arm.com> <20190124140032.8588-7-christoffer.dall@arm.com> <1978ee57-c7bd-e55a-4e77-ad0b4b62d1d1@arm.com> <20190222091848.21f7f8e6@why.wild-wind.fr.eu.org> From: Julien Grall Message-ID: <44bd2df6-8011-c77f-a83a-95c3529287c0@arm.com> Date: Fri, 22 Feb 2019 11:42:46 +0000 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.5.1 MIME-Version: 1.0 In-Reply-To: <20190222091848.21f7f8e6@why.wild-wind.fr.eu.org> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190222_034249_471633_AED7B7B4 X-CRM114-Status: GOOD ( 17.15 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "kvm@vger.kernel.org" , nd , Christoffer Dall , "linux-arm-kernel@lists.infradead.org" , "kvmarm@lists.cs.columbia.edu" Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi Marc, On 22/02/2019 09:18, Marc Zyngier wrote: > On Thu, 21 Feb 2019 11:02:56 +0000 > Julien Grall wrote: > > Hi Julien, > >> Hi Christoffer, >> >> On 24/01/2019 14:00, Christoffer Dall wrote: >>> Note that to avoid mapping the kvm_vmid_bits variable into hyp, we >>> simply forego the masking of the vmid value in kvm_get_vttbr and rely on >>> update_vmid to always assign a valid vmid value (within the supported >>> range). >> >> [...] >> >>> - kvm->arch.vmid = kvm_next_vmid; >>> + vmid->vmid = kvm_next_vmid; >>> kvm_next_vmid++; >>> - kvm_next_vmid &= (1 << kvm_vmid_bits) - 1; >>> - >>> - /* update vttbr to be used with the new vmid */ >>> - pgd_phys = virt_to_phys(kvm->arch.pgd); >>> - BUG_ON(pgd_phys & ~kvm_vttbr_baddr_mask(kvm)); >>> - vmid = ((u64)(kvm->arch.vmid) << VTTBR_VMID_SHIFT) & VTTBR_VMID_MASK(kvm_vmid_bits); >>> - kvm->arch.vttbr = kvm_phys_to_vttbr(pgd_phys) | vmid | cnp; >>> + kvm_next_vmid &= (1 << kvm_get_vmid_bits()) - 1; >> >> The arm64 version of kvm_get_vmid_bits does not look cheap. Indeed it required >> to read the sanitized value of SYS_ID_AA64MMFR1_EL1 that is implemented using >> the function bsearch. >> >> So wouldn't it be better to keep kvm_vmid_bits variable for use in update_vttbr()? > > How often does this happen? Can you measure this overhead at all? > > My understanding is that we hit this path on rollover only, having IPIed > all CPUs and invalidated all TLBs. I seriously doubt you can observe > any sort of overhead at all, given that it is so incredibly rare. But > feel free to prove me wrong! That would happen on roll-over and the first time you allocate VMID for the VM. I am planning to run some test with 3-bit VMIDs and provide them next week. Cheers, -- Julien Grall _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel