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=-18.3 required=3.0 tests=BAYES_00,DKIMWL_WL_MED, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_IN_DEF_DKIM_WL autolearn=unavailable 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 21CC5C433B4 for ; Mon, 12 Apr 2021 18:22:14 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EC00B61289 for ; Mon, 12 Apr 2021 18:22:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S244827AbhDLSW2 (ORCPT ); Mon, 12 Apr 2021 14:22:28 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49546 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229666AbhDLSW1 (ORCPT ); Mon, 12 Apr 2021 14:22:27 -0400 Received: from mail-il1-x12a.google.com (mail-il1-x12a.google.com [IPv6:2607:f8b0:4864:20::12a]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1B2D1C061574 for ; Mon, 12 Apr 2021 11:22:09 -0700 (PDT) Received: by mail-il1-x12a.google.com with SMTP id r5so3687632ilb.2 for ; Mon, 12 Apr 2021 11:22:09 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=pnS66VMnQJOfrQyl2K7TCo3s3dpgaNmmTPqQ0SzKz4s=; b=TqcrGz6KegN4pgqHPFivO3yGcoeZ9JJB6yZiEM5mAH0qxvLsR4SaGHWo0U+elcVTyI TSSKliuOOFqi3UJxhDqG7QSKqqO/9Vvx1mue/2PCnaDTlLpGSemF80v0dI143RexXv1j ady1yIvG8Zizv9go+vd2t3SqJ92h6aaa1kxViJfcAfqiAEyMtWO35CgIFHGfUqypuSgM LLYaLHfLyGEFQu/xArIC8HCiX4eCJnWv2LWr6FQcgDHl0ExNXTwCLJk9L+/GcXuLEeWu JJX+qm7lowNyE1UF6Sf229fqH1kvV8QIxPiwJy9vRjN//S/A0Do6mlTzid3FhRpUUW/d 6YgQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=pnS66VMnQJOfrQyl2K7TCo3s3dpgaNmmTPqQ0SzKz4s=; b=WegaV2g+Ct3jpzf/reS1IFNCSLiXDxYe2M3TgsmsEpIkea9kZZalnQ3HlkzbPwj8w2 a8d/JA8Q27MNpZk9E1tdh7ymrQaiIkPT3qkfko2XbwiR73L9RtNaoSlpOtmx+gB8++8F 2Tr+TWwCVE+jb3wHA438MNxbvj6BP7kWjKD8aCh20Kv/+bLLX0P3Ihdd9MsXfqMbOTI6 LAW3BNkmEkyQEj1QHWwPTMMqCXh0rLVPWc/UF1Wjef/iMPyIWPc3eIAoylXlmYFUoyBR qNLTliuiXFnuk3E0GXSgr+X3mtnwodvg99U25QX/K4UdE9TuH15T32V0gMCAsJU7Li4F n4cQ== X-Gm-Message-State: AOAM530GyivFC2fO2oXjfRDAki354CDHjGWlG+pSs7GQe+RmCvS6o2W6 h0k3TDNsK279EdW/aennKQBY1juIszwbYPLNsBS/LjNujc8= X-Google-Smtp-Source: ABdhPJwm+p1wkbZpFs/xEL+3HaD8HlLDy1XD8ohjBf6jJHtLg6V4pd8T8YN5xkFghqM9wK3gH/5Tb+0+prv0uWNCQzw= X-Received: by 2002:a05:6e02:1a49:: with SMTP id u9mr2895809ilv.306.1618251728283; Mon, 12 Apr 2021 11:22:08 -0700 (PDT) MIME-Version: 1.0 References: <20210401233736.638171-1-bgardon@google.com> <20210401233736.638171-10-bgardon@google.com> <4fc5960f-0b64-1cf5-d2c1-080d82d226a0@redhat.com> In-Reply-To: <4fc5960f-0b64-1cf5-d2c1-080d82d226a0@redhat.com> From: Ben Gardon Date: Mon, 12 Apr 2021 11:21:57 -0700 Message-ID: Subject: Re: [PATCH v2 09/13] KVM: x86/mmu: Allow zap gfn range to operate under the mmu read lock To: Paolo Bonzini Cc: LKML , kvm , Peter Xu , Sean Christopherson , Peter Shier , Peter Feiner , Junaid Shahid , Jim Mattson , Yulei Zhang , Wanpeng Li , Vitaly Kuznetsov , Xiao Guangrong Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Apr 2, 2021 at 12:53 AM Paolo Bonzini wrote: > > On 02/04/21 01:37, Ben Gardon wrote: > > +void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root, > > + bool shared) > > { > > gfn_t max_gfn = 1ULL << (shadow_phys_bits - PAGE_SHIFT); > > > > - lockdep_assert_held_write(&kvm->mmu_lock); > > + kvm_lockdep_assert_mmu_lock_held(kvm, shared); > > > > if (!refcount_dec_and_test(&root->tdp_mmu_root_count)) > > return; > > @@ -81,7 +92,7 @@ void kvm_tdp_mmu_put_root(struct kvm *kvm, struct kvm_mmu_page *root) > > list_del_rcu(&root->link); > > spin_unlock(&kvm->arch.tdp_mmu_pages_lock); > > > > - zap_gfn_range(kvm, root, 0, max_gfn, false, false); > > + zap_gfn_range(kvm, root, 0, max_gfn, false, false, shared); > > > > call_rcu(&root->rcu_head, tdp_mmu_free_sp_rcu_callback); > > Instead of patch 13, would it make sense to delay the zap_gfn_range and > call_rcu to a work item (either unconditionally, or only if > shared==false)? Then the zap_gfn_range would be able to yield and take > the mmu_lock for read, similar to kvm_tdp_mmu_zap_invalidated_roots. > > If done unconditionally, this would also allow removing the "shared" > argument to kvm_tdp_mmu_put_root, tdp_mmu_next_root and > for_each_tdp_mmu_root_yield_safe, so I would place that change before > this patch. > > Paolo > I tried that and it created problems. I believe the issue was that on VM teardown memslots would be freed and the memory reallocated before the root was torn down, resulting in a use-after free from mark_pfn_dirty. Perhaps this could be resolved by forcing memslot changes to wait until that work item was processed before returning. I can look into it but I suspect there will be a lot of "gotchas" involved.