From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762430AbbA3PKk (ORCPT ); Fri, 30 Jan 2015 10:10:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:7388 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750851AbbA3PKj (ORCPT ); Fri, 30 Jan 2015 10:10:39 -0500 Message-ID: <54CB9EE3.3030804@redhat.com> Date: Fri, 30 Jan 2015 16:10:27 +0100 From: Paolo Bonzini User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= CC: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Nadav Amit , Gleb Natapov Subject: Re: [PATCH 7/8] KVM: x86: avoid logical_map when it is invalid References: <1422568135-28402-1-git-send-email-rkrcmar@redhat.com> <1422568135-28402-8-git-send-email-rkrcmar@redhat.com> <54CB5101.4010701@redhat.com> <20150130145631.GB27414@potion.redhat.com> In-Reply-To: <20150130145631.GB27414@potion.redhat.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 30/01/2015 15:56, Radim Krčmář wrote: > 2015-01-30 10:38+0100, Paolo Bonzini: >> On 29/01/2015 22:48, Radim Krčmář wrote: >>> + if (hweight8(new->mode) != 1) >> >> Better (more optimized): >> >> if (new->mode & (new->mode - 1)) > > True, hweight needs to have X86_FEATURE_POPCNT to be efficient ... > > Do you know of a difference with it? > new->mode & (new->mode - 1) | hweight8(new->mode) != 1 > lea -0x1(%rax),%edi | popcnt %edi,%eax > test %eax,%edi | cmp $1,%eax x & (x - 1) is really hweight8(new->mode) > 1. So if new->mode == 0 it would have a different result. >> Please add a comment to kvm_irq_delivery_to_apic_fast to explain what >> you are doing. > > Would naming it kvm_apic_need_slow_delivery(), or something, be enough? Or kvm_apic_map_valid() perhaps? Paolo >>> + if (hweight8(map->mode) != 1) { >>> + /* Not deliverable with optimized map. */ >>> + ret = false; >>> + goto out; >>> + } >> >> Put this before the computation of cid and mda. The cid and mda are all >> wrong with a mixed map, and the result of the "if" before is influenced >> by the wrong cid. Fixed by patch 8, but better get it right here. > > Will do, > > thanks. >