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Tue, 20 Jul 2021 18:15:53 -0700 (PDT) Received: from google.com ([2409:10:2e40:5100:808c:1a13:1159:8184]) by smtp.gmail.com with ESMTPSA id x18sm23934960pfh.48.2021.07.20.18.15.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jul 2021 18:15:52 -0700 (PDT) Date: Wed, 21 Jul 2021 10:15:47 +0900 From: Sergey Senozhatsky To: Marc Zyngier Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support Message-ID: References: <20210709043713.887098-1-senozhatsky@chromium.org> <20210709043713.887098-5-senozhatsky@chromium.org> <874kcz33g5.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <874kcz33g5.wl-maz@kernel.org> X-Mailman-Approved-At: Wed, 21 Jul 2021 08:20:04 -0400 Cc: Joel Fernandes , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, Sergey Senozhatsky , Suleiman Souhlal , Will Deacon , kvmarm@lists.cs.columbia.edu, linux-arm-kernel@lists.infradead.org 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 (21/07/12 17:24), Marc Zyngier wrote: > > > > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > > { > > + kvm_update_vcpu_preempted(vcpu, true); > > This doesn't look right. With this, you are now telling the guest that > a vcpu that is blocked on WFI is preempted. This really isn't the > case, as it has voluntarily entered a low-power mode while waiting for > an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't > be running either. I suppose you are talking about kvm_vcpu_block(). Well, it checks kvm_vcpu_check_block() but then it simply schedule() out the vcpu process, which does look like "the vcpu is preempted". Once we sched_in() that vcpu process again we mark it as non-preempted, even though it remains in kvm wfx handler. Why isn't it right? Another call path is iret: __schedule() context_switch() prepare_task_switch() fire_sched_in_preempt_notifiers() kvm_sched_out() kvm_arch_vcpu_put() _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm 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=-2.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,FSL_HELO_FAKE,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 9FF7BC07E9B for ; Wed, 21 Jul 2021 01:17:26 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 668AB60FEA for ; 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Tue, 20 Jul 2021 18:15:52 -0700 (PDT) Date: Wed, 21 Jul 2021 10:15:47 +0900 From: Sergey Senozhatsky To: Marc Zyngier Cc: Sergey Senozhatsky , Will Deacon , Suleiman Souhlal , Joel Fernandes , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support Message-ID: References: <20210709043713.887098-1-senozhatsky@chromium.org> <20210709043713.887098-5-senozhatsky@chromium.org> <874kcz33g5.wl-maz@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <874kcz33g5.wl-maz@kernel.org> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210720_181555_662746_01D08F5D X-CRM114-Status: GOOD ( 13.40 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On (21/07/12 17:24), Marc Zyngier wrote: > > > > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > > { > > + kvm_update_vcpu_preempted(vcpu, true); > > This doesn't look right. With this, you are now telling the guest that > a vcpu that is blocked on WFI is preempted. This really isn't the > case, as it has voluntarily entered a low-power mode while waiting for > an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't > be running either. I suppose you are talking about kvm_vcpu_block(). Well, it checks kvm_vcpu_check_block() but then it simply schedule() out the vcpu process, which does look like "the vcpu is preempted". Once we sched_in() that vcpu process again we mark it as non-preempted, even though it remains in kvm wfx handler. Why isn't it right? Another call path is iret: __schedule() context_switch() prepare_task_switch() fire_sched_in_preempt_notifiers() kvm_sched_out() kvm_arch_vcpu_put() _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel 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=-4.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS 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 BAF9FC07E9B for ; Wed, 21 Jul 2021 01:16:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9078C61106 for ; Wed, 21 Jul 2021 01:16:37 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230025AbhGUAfq (ORCPT ); Tue, 20 Jul 2021 20:35:46 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:46694 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230030AbhGUAfR (ORCPT ); Tue, 20 Jul 2021 20:35:17 -0400 Received: from mail-pg1-x52b.google.com (mail-pg1-x52b.google.com [IPv6:2607:f8b0:4864:20::52b]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id ED63FC061762 for ; Tue, 20 Jul 2021 18:15:53 -0700 (PDT) Received: by mail-pg1-x52b.google.com with SMTP id o4so384912pgs.6 for ; Tue, 20 Jul 2021 18:15:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=chromium.org; s=google; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=UXoV+cGKQ4myvPfURbj+4IGhllQad57NXO7QIqiHQD4=; b=H3ES8RUOc7jcBhXKSSld1nbtEpTXLfbidaCzKfB/7XWZnxi/oMpreSNT8W9IF2UQFL j53LKazE8AZ9Zwuz9I4JcCE7RID2J6gT2zRjeiHMGJSJiWsWf5QNFSWGnQJdK6/c+m6e 281I99+7jaPLChAxNoOpxnsyI/mmQKcHRHYFI= X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=UXoV+cGKQ4myvPfURbj+4IGhllQad57NXO7QIqiHQD4=; b=CsqsA/uPn36X1wjyuUiwF/X1FHaoq1CIb+BrIpPBbwxRWJLPozoTsU/AT3+tQyfmVU AoNgKnN2pDemC+ZC28NdS4qdFyg0sAGf6Y/8/s2HbQBbVgFZ4yD1aw/wtihwKV9lX1R3 RrjsngYBnA69Nz5tleK6OkdiRHSiaTVoaooKib3/8YyMgIrDcyUjMIzZFm2mK3e4cMUh oDaMHToaicHJoghAIqYXC7+3K2FowwRWlW6Q7hLsuzLfeytsnXEMV/YLiw2s2U41bq1k n1nakTTHawtArNNZMlD/bdSUGrj32emhgYJWVJl+Do0Ql8I+gpD3voKsZ1+PO9P4OLz6 Kb5Q== X-Gm-Message-State: AOAM531tXpK2PBHMNfz6GXw7bstvF1Y0YTC4XeG9MYKGVxh0P24eFPW8 Q+ullMGWFtIbKwsyawKBNl/Ljw== X-Google-Smtp-Source: ABdhPJxfp5hGyASzFBCflJxvg/JXYrMBHZ4gp61qQS2+oVr0x7oYazVdBxY8Q9kTjoig37pYkCKYGg== X-Received: by 2002:a62:19c9:0:b029:32a:129f:542d with SMTP id 192-20020a6219c90000b029032a129f542dmr33857420pfz.8.1626830153493; Tue, 20 Jul 2021 18:15:53 -0700 (PDT) Received: from google.com ([2409:10:2e40:5100:808c:1a13:1159:8184]) by smtp.gmail.com with ESMTPSA id x18sm23934960pfh.48.2021.07.20.18.15.50 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 20 Jul 2021 18:15:52 -0700 (PDT) Date: Wed, 21 Jul 2021 10:15:47 +0900 From: Sergey Senozhatsky To: Marc Zyngier Cc: Sergey Senozhatsky , Will Deacon , Suleiman Souhlal , Joel Fernandes , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org Subject: Re: [PATCHv2 4/4] arm64: add host pv-vcpu-state support Message-ID: References: <20210709043713.887098-1-senozhatsky@chromium.org> <20210709043713.887098-5-senozhatsky@chromium.org> <874kcz33g5.wl-maz@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <874kcz33g5.wl-maz@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On (21/07/12 17:24), Marc Zyngier wrote: > > > > void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu) > > { > > + kvm_update_vcpu_preempted(vcpu, true); > > This doesn't look right. With this, you are now telling the guest that > a vcpu that is blocked on WFI is preempted. This really isn't the > case, as it has voluntarily entered a low-power mode while waiting for > an interrupt. Indeed, the vcpu isn't running. A physical CPU wouldn't > be running either. I suppose you are talking about kvm_vcpu_block(). Well, it checks kvm_vcpu_check_block() but then it simply schedule() out the vcpu process, which does look like "the vcpu is preempted". Once we sched_in() that vcpu process again we mark it as non-preempted, even though it remains in kvm wfx handler. Why isn't it right? Another call path is iret: __schedule() context_switch() prepare_task_switch() fire_sched_in_preempt_notifiers() kvm_sched_out() kvm_arch_vcpu_put()