From mboxrd@z Thu Jan 1 00:00:00 1970 From: Pavel Fedin Subject: RE: [PATCH v2 01/15] KVM: arm/arm64: VGIC: don't track used LRs in the distributor Date: Fri, 02 Oct 2015 15:39:44 +0300 Message-ID: <00f301d0fd0f$6b21ac10$41650430$@samsung.com> References: <1436538111-4294-1-git-send-email-andre.przywara@arm.com> <1436538111-4294-2-git-send-email-andre.przywara@arm.com> <00cb01d0fcf8$6a906000$3fb12000$@samsung.com> <560E5D2F.1000401@arm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: 'Marc Zyngier' , christoffer.dall@linaro.org, eric.auger@linaro.org, linux-arm-kernel@lists.infradead.org, kvm@vger.kernel.org To: 'Andre Przywara' , kvmarm@lists.cs.columbia.edu Return-path: Received: from mailout3.w1.samsung.com ([210.118.77.13]:17295 "EHLO mailout3.w1.samsung.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750846AbbJBMjt (ORCPT ); Fri, 2 Oct 2015 08:39:49 -0400 Received: from eucpsbgm2.samsung.com (unknown [203.254.199.245]) by mailout3.w1.samsung.com (Oracle Communications Messaging Server 7.0.5.31.0 64bit (built May 5 2014)) with ESMTP id <0NVL00AIAF6AVL20@mailout3.w1.samsung.com> for kvm@vger.kernel.org; Fri, 02 Oct 2015 13:39:46 +0100 (BST) In-reply-to: <560E5D2F.1000401@arm.com> Content-language: ru Sender: kvm-owner@vger.kernel.org List-ID: Hello! > Can't you use the ELRSR bitmap instead? The idea of lr_used sounds like > a moot optimization to me. This perfectly works on 4.2, but will break HW interrupt forwarding on 4.3. If you look at 4.3 __kvm_vgic_sync_hwstate(), you'll notice that for HW interrupts lr_used and elrsr_ptr will diverge at this point, and this function actually brings them into sync. And it relies on lr_used for the loop to operate correctly (no idea why we use "for" loop here with extra check instead of "for_each_set_bit(lr, vgic_cpu->lr_used, vgic->nr_lr)", looks stupid to me). Kind regards, Pavel Fedin Expert Engineer Samsung Electronics Research center Russia