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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 794F6C433FE for ; Tue, 30 Nov 2021 16:18:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238673AbhK3QV0 (ORCPT ); Tue, 30 Nov 2021 11:21:26 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53348 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238704AbhK3QUL (ORCPT ); Tue, 30 Nov 2021 11:20:11 -0500 Received: from mail-ed1-x536.google.com (mail-ed1-x536.google.com [IPv6:2a00:1450:4864:20::536]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 86496C061574; Tue, 30 Nov 2021 08:16:43 -0800 (PST) Received: by mail-ed1-x536.google.com with SMTP id g14so89072912edb.8; Tue, 30 Nov 2021 08:16:43 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=sender:message-id:date:mime-version:user-agent:subject :content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=mzJ6JGKckSdI9QVOm/WqgiUaO2eWSx9RlGb8CUcCl4w=; b=BGtDTNJa6yl+3sQvIYCTCRiKOhxJrICeiKUd60ghIrHc2JQUA+Eqx2tTD5dNTf3ZkG XWZUJ3n2XZoQGZ/95AZ8JD2PJM4Fxnr3T23YyBkCkacY9C1VdaMM/UVQx7kyizhGWIng 6um8VK7YEm4EcrQbDz/mH71PuCrfbNbLl4LRDoKILRik+pciV4t9X/JG9kU5vr/45n+Y JPywVfgr1/KmeuRNF+9Gcu3ECbqpdLhtH4T3lhTVNa5ruU4PPAGual4qZuYTPRXe2DRJ Anwb16sT8Yz+bYLJouW98HYyI8WWk4qFDE7zi9SRSvGASwtKDTQzoQOD75liaDJbMulJ nFMA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:sender:message-id:date:mime-version:user-agent :subject:content-language:to:cc:references:from:in-reply-to :content-transfer-encoding; bh=mzJ6JGKckSdI9QVOm/WqgiUaO2eWSx9RlGb8CUcCl4w=; b=tPYtuJzR5vqafd66Yk2WlpWNonnyCmATlzZRnzHxEWCPePdaQdKFimFTkXJdCbbo+I cdZSH5XOqnIoFxFuZmYcRHzubjhffORnTy9b8avNNlSDjeXX/oDap8dbTZ0niV4SCcPE nBNC27H8LbAToFWkux2JAOFzJY/O/ptDmHJL+mfs1DrYHioUia5LrnzTUCRF+3+/uP+J wQb4hhAXpwuLXA7dhufShfBPCAl4ksLIEeGMk3X1I8+Bvser1PbV+ehX+ntafwRHFJuj UcvpyDZFFIE41Ucl3hxa5tD0BZhNKbO1UWgm0mTsXu5beR3O7jbqcRtDaN5y+K+vZlqg wM6g== X-Gm-Message-State: AOAM533s42An43zgH6e3VLJ/UD9eZr7NQqWUQY/anWun5jQ/UocTRSED cJZ//Va8c+gs276h3wwVk1E= X-Google-Smtp-Source: ABdhPJw2yRCId66xKjvWGOtJo37/MAUXUgEWlbSJBwdXpQc8hXYzqfCbuoni1K2nh9m8fWU22U0H2w== X-Received: by 2002:a05:6402:5188:: with SMTP id q8mr86125381edd.181.1638289002148; Tue, 30 Nov 2021 08:16:42 -0800 (PST) Received: from ?IPV6:2001:b07:add:ec09:c399:bc87:7b6c:fb2a? ([2001:b07:add:ec09:c399:bc87:7b6c:fb2a]) by smtp.googlemail.com with ESMTPSA id hr17sm9270702ejc.57.2021.11.30.08.16.34 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 30 Nov 2021 08:16:41 -0800 (PST) Sender: Paolo Bonzini Message-ID: <1469b131-cd76-e8bb-304b-73c59e81cb3b@redhat.com> Date: Tue, 30 Nov 2021 17:16:29 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 Subject: Re: [PATCH 27/28] KVM: x86/mmu: Do remote TLB flush before dropping RCU in TDP MMU resched Content-Language: en-US To: Sean Christopherson Cc: Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Hou Wenlong , Ben Gardon References: <20211120045046.3940942-1-seanjc@google.com> <20211120045046.3940942-28-seanjc@google.com> From: Paolo Bonzini In-Reply-To: Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/30/21 16:45, Sean Christopherson wrote: >> Couldn't this sleep in kvm_make_all_cpus_request, whilst in an RCU read-side >> critical section? > No. And if kvm_make_all_cpus_request() can sleep, the TDP MMU is completely hosed > as tdp_mmu_zap_spte_atomic() and handle_removed_tdp_mmu_page() currently call > kvm_flush_remote_tlbs_with_range() while under RCU protection. > > kvm_make_all_cpus_request_except() disables preemption via get_cpu(), and > smp_call_function() doubles down on disabling preemption as the inner helpers > require preemption to be disabled, so anything below them should complain if > there's a might_sleep(). hv_remote_flush_tlb_with_range() takes a spinlock, so > nothing in there should be sleeping either. Yeah, of course you're right. Paolo