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=-3.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 A7FC8C4338F for ; Thu, 12 Aug 2021 13:36:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7BEBE6101E for ; Thu, 12 Aug 2021 13:36:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237318AbhHLNgq (ORCPT ); Thu, 12 Aug 2021 09:36:46 -0400 Received: from foss.arm.com ([217.140.110.172]:43226 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232356AbhHLNgm (ORCPT ); Thu, 12 Aug 2021 09:36:42 -0400 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 45EB51042; Thu, 12 Aug 2021 06:36:17 -0700 (PDT) Received: from e113632-lin (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5CE103F70D; Thu, 12 Aug 2021 06:36:16 -0700 (PDT) From: Valentin Schneider To: Marc Zyngier Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Thomas Gleixner , Lorenzo Pieralisi , Vincenzo Frascino Subject: Re: [PATCH v3 02/13] genirq: Define ack_irq() and eoi_irq() helpers In-Reply-To: <87a6ln9k7i.wl-maz@kernel.org> References: <20210629125010.458872-1-valentin.schneider@arm.com> <20210629125010.458872-3-valentin.schneider@arm.com> <87a6ln9k7i.wl-maz@kernel.org> Date: Thu, 12 Aug 2021 14:36:11 +0100 Message-ID: <877dgq9450.mognet@arm.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/08/21 08:49, Marc Zyngier wrote: > On Tue, 29 Jun 2021 13:49:59 +0100, > Valentin Schneider wrote: >> +void eoi_irq(struct irq_desc *desc) >> +{ >> + desc->irq_data.chip->irq_eoi(&desc->irq_data); >> + >> + if (desc->irq_data.chip->flags & IRQCHIP_AUTOMASKS_FLOW) >> + irq_state_clr_flow_masked(desc); > > I just realised that this has a good chance to result in a mess with > KVM, and specially the way we let the vGIC deactivate an interrupt > directly from the guest, without any SW intervention (the magic HW bit > in the LRs). > I didn't think to consider those. It can't ever be simple, can it... > With this, interrupts routed to a guest (such as the timers) will > always have the IRQD_IRQ_FLOW_MASKED flag set, which will never be > cleared. > > I wonder whether this have a chance to interact badly with > mask/unmask, or with the rest of the flow... > Isn't it the other way around? That is, eoi_irq() will clear IRQD_IRQ_FLOW_MASKED regardless of what happens within chip->irq_eoi(), so we would end up with !IRQD_IRQ_FLOW_MASKED even if the (physical) IRQ remains Active (irqd_is_forwarded_to_vcpu() case). This does not entirely match reality (if the IRQ is still Active then it is still "flow-masked"), but AFAICT this doesn't impact our handling of forwarded IRQs: IRQD_IRQ_FLOW_MASKED is only really relevant from ack_irq() to eoi_irq(), and deactivation-from-the-guest (propagated via LR.HW=1) happens after that.