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=-2.3 required=3.0 tests=DKIM_INVALID,DKIM_SIGNED, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_2 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 9C348C43331 for ; Wed, 1 Apr 2020 10:28:10 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 28FED20787 for ; Wed, 1 Apr 2020 10:28:09 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (1024-bit key) header.d=kernel.org header.i=@kernel.org header.b="fnoHwQbV" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 28FED20787 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id A66B24B0CE; Wed, 1 Apr 2020 06:28:09 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@kernel.org Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id MK-RKkVex8Oo; Wed, 1 Apr 2020 06:28:08 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 9F4DC4B0D1; Wed, 1 Apr 2020 06:28:08 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id D6B074B0BF for ; Wed, 1 Apr 2020 06:28:07 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id quztL5N-UOJT for ; Wed, 1 Apr 2020 06:28:06 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id B35424B0BA for ; Wed, 1 Apr 2020 06:28:06 -0400 (EDT) Received: from disco-boy.misterjones.org (disco-boy.misterjones.org [51.254.78.96]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 8AACD20678; Wed, 1 Apr 2020 10:28:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1585736885; bh=ZGIFCj7egJvoPFEFYXQPBwun/lzoQ4tkiFuG/7SntGo=; h=Date:From:To:Cc:Subject:In-Reply-To:References:From; b=fnoHwQbV/Vrntb3eTwRTe1ELFyq1lZ0qBZBP5bKg8eVlicaVTKIGXwbAjsx8lRuu+ sOtHc9u6WqP7rgTmSMlnHfIvg3h/WbQJgQYOFz/QmIsRhzOrngo9fDYFaTmpQJuoSz hI+E2NpYeLGgUxSuSCqMue/ercrKBbSVRoRX6cXo= Received: from 78.163-31-62.static.virginmediabusiness.co.uk ([62.31.163.78] helo=why) by disco-boy.misterjones.org with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1jJabL-00HTVP-97; Wed, 01 Apr 2020 11:28:03 +0100 Date: Wed, 1 Apr 2020 11:27:57 +0100 From: Marc Zyngier To: Zenghui Yu Subject: Re: [PATCH] KVM: arm64: vgic-v3: Clear pending bit in guest memory after synchronization Message-ID: <20200401112757.6716cbf3@why> In-Reply-To: References: <20200331031245.1562-1-yuzenghui@huawei.com> <20200331090709.17d2087d@why> Organization: Approximate X-Mailer: Claws Mail 3.17.5 (GTK+ 2.24.32; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-SA-Exim-Connect-IP: 62.31.163.78 X-SA-Exim-Rcpt-To: yuzenghui@huawei.com, kvmarm@lists.cs.columbia.edu, eric.auger@redhat.com, andre.przywara@arm.com, james.morse@arm.com, julien.thierry.kdev@gmail.com, suzuki.poulose@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, wanghaibin.wang@huawei.com X-SA-Exim-Mail-From: maz@kernel.org X-SA-Exim-Scanned: No (on disco-boy.misterjones.org); SAEximRunCond expanded to false Cc: andre.przywara@arm.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Tue, 31 Mar 2020 17:11:37 +0800 Zenghui Yu wrote: Hi Zenghui, > Hi Marc, > > On 2020/3/31 16:07, Marc Zyngier wrote: > > Hi Zenghui, [...] > >> > > I've been thinking about this, and I wonder why we don't simply clear > > the whole pending table instead of carefully wiping it one bit at a > > time. My reasoning is that if a LPI isn't mapped, then it cannot be made > > pending the first place. > > A writing to GICR_CTLR.EnableLPIs can happen in parallel with MAPTI/INT > command sequence, where the new LPI is mapped to *this* vcpu and made > pending, wrong? I think commit 7d8b44c54e0c had described it in detail. I'm not sure this commit is relevant here. It describes how the configuration is picked up by MAPTI, not how the pending bit got there the first place. > But thinking that we cache the pending bit in pending_latch (instead of > writing the corresponding bit in guest memory) when a LPI is made > pending, it seems to be safe to clear the whole pending table here. Yes, and this is my worry. The spec is pretty vague about what the behaviour of the redistributor is when something is set in the pending table. At the moment, we treat these bits as if they had been generated by a translation, but we do so inconsistently: we only pick these bits up and generate a LPI if there is a mapping at the ITS level. If these bits are relevant, we should forward a LPI to the CPU. It feels we're in UNPREDICTIBLE land... > > > > > And I think there is a similar issue in vgic_v3_lpi_sync_pending_status(). > > Why sync something back from the pending table when the LPI wasn't > > mapped yet? > > vgic_v3_lpi_sync_pending_status() can be called on the ITE restore path: > vgic_its_restore_ite/vgic_add_lpi/vgic_v3_lpi_sync_pending_status. > We should rely on it to sync the pending bit from guest memory (which > was saved on the source side). The fact that we have *two* paths to restore pending bits is pretty annoying. There is certainly some scope for simplification here. Thanks, M. -- Jazz is not dead. It just smells funny... _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm