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 C306AC433F5 for ; Sat, 20 Nov 2021 04:53:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237753AbhKTE4E (ORCPT ); Fri, 19 Nov 2021 23:56:04 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54994 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S235688AbhKTEyn (ORCPT ); Fri, 19 Nov 2021 23:54:43 -0500 Received: from mail-pl1-x64a.google.com (mail-pl1-x64a.google.com [IPv6:2607:f8b0:4864:20::64a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 410E0C061398 for ; Fri, 19 Nov 2021 20:51:15 -0800 (PST) Received: by mail-pl1-x64a.google.com with SMTP id l14-20020a170903120e00b00143cc292bc3so5720337plh.1 for ; Fri, 19 Nov 2021 20:51:15 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=reply-to:date:in-reply-to:message-id:mime-version:references :subject:from:to:cc; bh=k4NHpd3E7FQzbwVOtcdF5b2uNcYEHobxgRNhAQdrHYQ=; b=R+xGNzJ/vyiSC7Df9o413MvDVFxJTTeMRZeyITgFauzdVqZSc6VXOc17nRygs8c2+b /4/A+WUHuA7gcYI5tI+HIGS/YB/HhNmaFIPsk7vzx/9DVa3kvR4vgQH2w9gGlrTRdUQs kiVX+LK8amz1r6Il5upaLUMyr5YfL1fZK+HlKlmzIk6IoIS5XgMgp4p+FjBSx9IAXCSb JlvdZMI1kg1bf1usOJtVa0X/mZWXVdZmTdgHMafPKv6IyVvZWgecT4d0D+jZK5rchKZH z6SP6HrbxbXZHG36efuvIXr4JBaBbnEl9YyBe+n5DWMFo9wMzEQ6VfDLEyF+M98y0PAP kl5Q== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:reply-to:date:in-reply-to:message-id :mime-version:references:subject:from:to:cc; bh=k4NHpd3E7FQzbwVOtcdF5b2uNcYEHobxgRNhAQdrHYQ=; b=1OPyhCqWIyx9O3dgxllZ9Fw38buH147T9sUjWj2NK4h791EURjYOUCTMqtBLMIaLys ZeKvic4s01ZhsV2RaYfNweMeuaW8IXlS68Z2Zjurz+kUG5z/C7BNcuvgv9wg4uI/BZwP WkFoaRk9Hlw4CNjkYg5bji/lq/gGGgRPVXhhEB9d2gBZHCXWhKDdRz0owolruvjvZl80 LevMTHHkUhFmzrdlZB7VpoCwfX1iiCy8EikcAkNd2s06dg1DUv5G3BkGBEyLXTSAXmoq mPmM6hKwp0z1T4U8IouWGcREwb6kwHqf9LnThrZWLOEVB3EcZnFx+McGItBy/gNbw7ms 34jQ== X-Gm-Message-State: AOAM53154hjMMWTmSTumsyLOihRYnyPwnVMZxlKJrWfMLTOgAiO4v0vg JvO0E2Mcg8MBT98jViTg8L8kW6Pcdv4= X-Google-Smtp-Source: ABdhPJwgT/yEVp7NlXrsEHaMuqvEPid69UudN0pRgbth0GHzfVfKZ1tPqnrZWw18DWTXLnGL3vO8zi+am/E= X-Received: from seanjc.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:3e5]) (user=seanjc job=sendgmr) by 2002:a62:9215:0:b0:49f:e38b:d043 with SMTP id o21-20020a629215000000b0049fe38bd043mr28037702pfd.86.1637383874643; Fri, 19 Nov 2021 20:51:14 -0800 (PST) Reply-To: Sean Christopherson Date: Sat, 20 Nov 2021 04:50:31 +0000 In-Reply-To: <20211120045046.3940942-1-seanjc@google.com> Message-Id: <20211120045046.3940942-14-seanjc@google.com> Mime-Version: 1.0 References: <20211120045046.3940942-1-seanjc@google.com> X-Mailer: git-send-email 2.34.0.rc2.393.gf8c9666880-goog Subject: [PATCH 13/28] KVM: x86/mmu: Drop RCU after processing each root in MMU notifier hooks From: Sean Christopherson To: Paolo Bonzini Cc: Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org, Hou Wenlong , Ben Gardon Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Drop RCU protection after processing each root when handling MMU notifier hooks that aren't the "unmap" path, i.e. aren't zapping. Temporarily drop RCU to let RCU do its thing between roots, and to make it clear that there's no special behavior that relies on holding RCU across all roots. Currently, the RCU protection is completely superficial, it's necessary only to make rcu_dereference() of SPTE pointers happy. A future patch will rely on holding RCU as a proxy for vCPUs in the guest, e.g. to ensure shadow pages aren't freed before all vCPUs do a TLB flush (or rather, acknowledge the need for a flush), but in that case RCU needs to be held until the flush is complete if and only if the flush is needed because a shadow page may have been removed. And except for the "unmap" path, MMU notifier events cannot remove SPs (don't toggle PRESENT bit, and can't change the PFN for a SP). Signed-off-by: Sean Christopherson --- arch/x86/kvm/mmu/tdp_mmu.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 06b500fab248..3ff7b4cd7d0e 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1079,18 +1079,19 @@ static __always_inline bool kvm_tdp_mmu_handle_gfn(struct kvm *kvm, lockdep_assert_held_write(&kvm->mmu_lock); - rcu_read_lock(); - /* * Don't support rescheduling, none of the MMU notifiers that funnel * into this helper allow blocking; it'd be dead, wasteful code. */ for_each_tdp_mmu_root(kvm, root, range->slot->as_id) { + rcu_read_lock(); + tdp_root_for_each_leaf_pte(iter, root, range->start, range->end) ret |= handler(kvm, &iter, range); + + rcu_read_unlock(); } - rcu_read_unlock(); return ret; } -- 2.34.0.rc2.393.gf8c9666880-goog