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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS 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 91D32C43144 for ; Fri, 29 Jun 2018 13:10:21 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 47C3B27F29 for ; Fri, 29 Jun 2018 13:10:21 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 47C3B27F29 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S936487AbeF2NKT (ORCPT ); Fri, 29 Jun 2018 09:10:19 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:58310 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S933132AbeF2NKR (ORCPT ); Fri, 29 Jun 2018 09:10:17 -0400 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 38882818F037; Fri, 29 Jun 2018 13:10:17 +0000 (UTC) Received: from vitty.brq.redhat.com.redhat.com (unknown [10.43.2.155]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 46B2F21565E1; Fri, 29 Jun 2018 13:10:15 +0000 (UTC) From: Vitaly Kuznetsov To: Roman Kagan Cc: kvm@vger.kernel.org, x86@kernel.org, Paolo Bonzini , Radim =?utf-8?B?S3LEjW3DocWZ?= , "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , "Michael Kelley \(EOSG\)" , Mohammed Gamal , Cathy Avery , Wanpeng Li , linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 2/5] KVM: x86: hyperv: introduce vp_index_to_vcpu_idx mapping References: <20180628135313.17468-1-vkuznets@redhat.com> <20180628135313.17468-3-vkuznets@redhat.com> <20180629101134.GA15656@rkaganb.sw.ru> <87y3exdh2o.fsf@vitty.brq.redhat.com> <20180629111227.GB15656@rkaganb.sw.ru> <87tvplddrr.fsf@vitty.brq.redhat.com> <20180629125216.GC15656@rkaganb.sw.ru> Date: Fri, 29 Jun 2018 15:10:14 +0200 In-Reply-To: <20180629125216.GC15656@rkaganb.sw.ru> (Roman Kagan's message of "Fri, 29 Jun 2018 15:52:16 +0300") Message-ID: <87h8lld9hl.fsf@vitty.brq.redhat.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 2.78 on 10.11.54.6 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 29 Jun 2018 13:10:17 +0000 (UTC) X-Greylist: inspected by milter-greylist-4.5.16 (mx1.redhat.com [10.11.55.8]); Fri, 29 Jun 2018 13:10:17 +0000 (UTC) for IP:'10.11.54.6' DOMAIN:'int-mx06.intmail.prod.int.rdu2.redhat.com' HELO:'smtp.corp.redhat.com' FROM:'vkuznets@redhat.com' RCPT:'' Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Roman Kagan writes: > On Fri, Jun 29, 2018 at 01:37:44PM +0200, Vitaly Kuznetsov wrote: >> The problem we're trying to solve here is: with PV TLB flush and IPI we >> need to walk through the supplied list of VP_INDEXes and get VCPU >> ids. Usually they match. But in case they don't [...] > > Why wouldn't they *in practice*? Only if the userspace wanted to be > funny and assigned VP_INDEXes randomly? I'm not sure we need to > optimize for this case. Can someone please remind me why we allow userspace to change it in the first place? > > Note that the userspace can actually do nasty things with these > VP_INDEXes, like, say, have them non-unique. We need to be resilent to > it, but don't need to optimize for it. > > I think I'd rather have a warning in kvm_hv_set_msr if the VP_INDEX > being assigned is not equal to the vcpu index, and start worrying about > optimization only if this warning starts being triggered by real > hypervisor applications. > > Anyway I don't see an urgent need to bloat this patchset with optimizing > this translation; it can be done separately, if needed. Sure, I can use get_vcpu_by_vpidx() in the patchset pretending that is's always fast and if we find a valid case where it is not - we'll just optimize it later. Sounds sane to me. -- Vitaly