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=-6.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=ham 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 EEA3CC5DF63 for ; Wed, 6 Nov 2019 18:04:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BCBCB217D7 for ; Wed, 6 Nov 2019 18:04:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="h75vWf1k" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1732404AbfKFSEf (ORCPT ); Wed, 6 Nov 2019 13:04:35 -0500 Received: from mail-oi1-f194.google.com ([209.85.167.194]:35563 "EHLO mail-oi1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726616AbfKFSEf (ORCPT ); Wed, 6 Nov 2019 13:04:35 -0500 Received: by mail-oi1-f194.google.com with SMTP id n16so21861179oig.2 for ; Wed, 06 Nov 2019 10:04:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=intel-com.20150623.gappssmtp.com; s=20150623; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=/0n4m9isT+Ck0ZHgj9nNKHVTcK5i7dBz9IQntg3gksQ=; b=h75vWf1kfqT7WCo9oPzlH2IwFP6eMdStUMP0AfAWnCe9OTYcu6TEsPQN+yx0WoqEfq E9HYz+A8UEG4Su4we8xTN//jPaDiLogimAXPPq7m0mNmordt3w8sFggaWtnyUYem3jnV 6YlDe2ZG+OUVXEku1BqAlx0/+2QNx95Nabu6PSJOBfwuZ+nVV7z5t51ZXYtFHS66k90N GVDBPQilrV8oMQ7DNQWzztigOCU2RVft+4pAWjC/QdLhQ/XhuHntvIeT7H1UOhmG8tMz llLeRyvDxLSm3aV446uh3sdLt05Xn/RhAJAmzbveqLU3H+9a7DKOraTRf5EWciCNfYOw VwtQ== 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=/0n4m9isT+Ck0ZHgj9nNKHVTcK5i7dBz9IQntg3gksQ=; b=P45mPpCZc6wRRTPKJuXn6wirCvqZe7D+czzLhDdRf7pjCqAjv5QdIGXjovd49QKrbC MacNtsQse+OJ4kupJNntKYs9qYhAw6+wl/X299IQyTU7AP7uW9t7vdGy4F8PkMuJvHSX lAV5b+xALHOWkWDeaZnGQZIThfRPsy8M5kuIGMnJYpzUIpzDLalQ4UhzbUrgaRs8nxKW Ruv4PNjqX9MdZbnxeSnzx5UyYaemU/ufAp9k/RmHQHnh5d9cGfKeAm4bYSmlVBrqSriN k19TC3sztB8KrmixIorLyKDPlCdIwi5TPCTRUIdc5c/NLwldHUZR/PSdlxPIIiGlLkeV A6CA== X-Gm-Message-State: APjAAAVRGV7eCO61fNIWfndRIgYdRFZ8+4OfWAYxdgc0aiaqp6vzumOj zrc42RK1tBuMTId/wI75NGsEzGrpESrsL1vfYQSE8Q== X-Google-Smtp-Source: APXvYqz322KPWE0McOPQ2HU7vzGL4faH1DPYPThcfro4U804rY+815CpZXkhVTFxQRmu8DE2tmavfFznwplkC4fdonI= X-Received: by 2002:aca:ead7:: with SMTP id i206mr3543339oih.0.1573063474058; Wed, 06 Nov 2019 10:04:34 -0800 (PST) MIME-Version: 1.0 References: <20191106170727.14457-1-sean.j.christopherson@intel.com> <20191106170727.14457-2-sean.j.christopherson@intel.com> In-Reply-To: <20191106170727.14457-2-sean.j.christopherson@intel.com> From: Dan Williams Date: Wed, 6 Nov 2019 10:04:22 -0800 Message-ID: Subject: Re: [PATCH 1/2] KVM: MMU: Do not treat ZONE_DEVICE pages as being reserved To: Sean Christopherson Cc: Paolo Bonzini , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , KVM list , Linux Kernel Mailing List , Adam Borowski , David Hildenbrand Content-Type: text/plain; charset="UTF-8" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Nov 6, 2019 at 9:07 AM Sean Christopherson wrote: > > Explicitly exempt ZONE_DEVICE pages from kvm_is_reserved_pfn() and > instead manually handle ZONE_DEVICE on a case-by-case basis. For things > like page refcounts, KVM needs to treat ZONE_DEVICE pages like normal > pages, e.g. put pages grabbed via gup(). But KVM needs special handling > in other flows where ZONE_DEVICE pages lack the underlying machinery, > e.g. when setting accessed/dirty bits and shifting refcounts for > transparent huge pages. > > This fixes a hang reported by Adam Borowski[*] in dev_pagemap_cleanup() > when running a KVM guest backed with /dev/dax memory, as KVM straight up > doesn't put any references to ZONE_DEVICE pages acquired by gup(). > > [*] http://lkml.kernel.org/r/20190919115547.GA17963@angband.pl > > Reported-by: Adam Borowski > Debugged-by: David Hildenbrand > Cc: Dan Williams > Cc: stable@vger.kernel.org > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/mmu.c | 8 ++++---- > include/linux/kvm_host.h | 1 + > virt/kvm/kvm_main.c | 19 +++++++++++++++---- > 3 files changed, 20 insertions(+), 8 deletions(-) > > diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c > index 24c23c66b226..bf82b1f2e834 100644 > --- a/arch/x86/kvm/mmu.c > +++ b/arch/x86/kvm/mmu.c > @@ -3306,7 +3306,7 @@ static void transparent_hugepage_adjust(struct kvm_vcpu *vcpu, > * here. > */ > if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn) && > - level == PT_PAGE_TABLE_LEVEL && > + !kvm_is_zone_device_pfn(pfn) && level == PT_PAGE_TABLE_LEVEL && > PageTransCompoundMap(pfn_to_page(pfn)) && > !mmu_gfn_lpage_is_disallowed(vcpu, gfn, PT_DIRECTORY_LEVEL)) { > unsigned long mask; > @@ -5914,9 +5914,9 @@ static bool kvm_mmu_zap_collapsible_spte(struct kvm *kvm, > * the guest, and the guest page table is using 4K page size > * mapping if the indirect sp has level = 1. > */ > - if (sp->role.direct && > - !kvm_is_reserved_pfn(pfn) && > - PageTransCompoundMap(pfn_to_page(pfn))) { > + if (sp->role.direct && !kvm_is_reserved_pfn(pfn) && > + !kvm_is_zone_device_pfn(pfn) && > + PageTransCompoundMap(pfn_to_page(pfn))) { > pte_list_remove(rmap_head, sptep); > > if (kvm_available_flush_tlb_with_range()) > diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h > index a817e446c9aa..4ad1cd7d2d4d 100644 > --- a/include/linux/kvm_host.h > +++ b/include/linux/kvm_host.h > @@ -966,6 +966,7 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu); > void kvm_vcpu_kick(struct kvm_vcpu *vcpu); > > bool kvm_is_reserved_pfn(kvm_pfn_t pfn); > +bool kvm_is_zone_device_pfn(kvm_pfn_t pfn); > > struct kvm_irq_ack_notifier { > struct hlist_node link; > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index b8534c6b8cf6..0a781b1fb8f0 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -151,12 +151,23 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm, > > bool kvm_is_reserved_pfn(kvm_pfn_t pfn) > { > + /* > + * ZONE_DEVICE pages currently set PG_reserved, but from a refcounting > + * perspective they are "normal" pages, albeit with slightly different > + * usage rules. > + */ > if (pfn_valid(pfn)) > - return PageReserved(pfn_to_page(pfn)); > + return PageReserved(pfn_to_page(pfn)) && > + !is_zone_device_page(pfn_to_page(pfn)); This is racy unless you can be certain that the pfn and resulting page has already been pinned by get_user_pages(). This is why I told David to steer clear of adding more is_zone_device_page() usage, it's difficult to audit. Without an existing pin the metadata to determine whether a page is ZONE_DEVICE or not could be in the process of being torn down. Ideally KVM would pass around a struct { struct page *page, unsigned long pfn } tuple so it would not have to do this "recall context" dance on every pfn operation.