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=-0.7 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 007BCC5DF60 for ; Tue, 5 Nov 2019 23:30:14 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 85E4421882 for ; Tue, 5 Nov 2019 23:30:13 +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="ax5HR98W" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 85E4421882 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 3AB756B0003; Tue, 5 Nov 2019 18:30:13 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id 35BCC6B0005; Tue, 5 Nov 2019 18:30:13 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 271A76B0006; Tue, 5 Nov 2019 18:30:13 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0161.hostedemail.com [216.40.44.161]) by kanga.kvack.org (Postfix) with ESMTP id 0E49F6B0003 for ; Tue, 5 Nov 2019 18:30:13 -0500 (EST) Received: from smtpin27.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay01.hostedemail.com (Postfix) with SMTP id B7C64180AD820 for ; Tue, 5 Nov 2019 23:30:12 +0000 (UTC) X-FDA: 76123819464.27.chair00_59084eaf8824f X-HE-Tag: chair00_59084eaf8824f X-Filterd-Recvd-Size: 7069 Received: from mail-ot1-f65.google.com (mail-ot1-f65.google.com [209.85.210.65]) by imf17.hostedemail.com (Postfix) with ESMTP for ; Tue, 5 Nov 2019 23:30:11 +0000 (UTC) Received: by mail-ot1-f65.google.com with SMTP id z6so19243155otb.2 for ; Tue, 05 Nov 2019 15:30:11 -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=R3DmgtbuDvl/nfkrniY8Ba73gr9pACG77rpNCqLOyTA=; b=ax5HR98WH4xqZvWHcyzuHRNGmZvT7I9m7xhGJ1uY8PDybcgBe1VmfyCLXrE48zy0BX vWcIHu6UYoH8HknqTIdU6Y+LYlECfapFpwLBsIAucTcvwTRYHtKiZpX6HfdTzXXEPEnk HWjqS+gQejFktk2XITcuM0n+yeF5sQPBkc+kK/6meBz8x9VvLBJ24hrRrJof+Z2QZCIS ZvRSXKB24+uJoWcJtAJmQHL6SW1XP2EN8QixZwZsl13dmEYE2GJMvXzgHqy355aGvDQ3 F0zrp/0LqNIWlZiKW6TlpU1rB2bmBt1brju1GqeiJ5NinFlVYYEE2UC84COw1zeJ61L+ MXMw== 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=R3DmgtbuDvl/nfkrniY8Ba73gr9pACG77rpNCqLOyTA=; b=PP+6EvxJERj3BybYqdJHvuyWvH3X5gi09J/5/S9Hybnrz/a5/882M4o78zpxzbszPz U7FmpOluC5+UT8mPmDyFOKUGUbH6j6vy+9/EMGEviLwSxpGOtKTL9oIGplQYJVl0kwtA 0AeSeYghKi5kB+s34zFWZvrgVNIJ0o93mbSVM5DthZxKDjmqUeDnN5q19dWX2ikG1Lhr wb4aKoDgReL/gGVcQpYnPFYXBop61mpjWpXnrYhSQiaplk9WisCrY3KTxjQ9s1aoRmDH 0ghNU02Ud7H2tYnDxeSa1zRgU9rn+TIP+P9BQ1CTwM02ZCKpvO8qMHjCI4pDtVGtibaD YXRg== X-Gm-Message-State: APjAAAVsuZMPxYZqV6JwCp/Jh16ycNlfMFGqN5ZYbb/dQ1JhXaGGfBq5 MsdRDtWNoGqJS3DLfIWeKMHw9zmvikfWvyN13ADPuQ== X-Google-Smtp-Source: APXvYqyxc+DmPQQN5aSk0dtRzKoWLg9GygXu/1AciWksnhJhFNdAydFP0T3vz9JQ5vwewxa4ElAmJqPI0FG8eQ5kblQ= X-Received: by 2002:a9d:5f11:: with SMTP id f17mr24157383oti.207.1572996611041; Tue, 05 Nov 2019 15:30:11 -0800 (PST) MIME-Version: 1.0 References: <20191024120938.11237-1-david@redhat.com> <20191024120938.11237-4-david@redhat.com> <01adb4cb-6092-638c-0bab-e61322be7cf5@redhat.com> <613f3606-748b-0e56-a3ad-1efaffa1a67b@redhat.com> <20191105160000.GC8128@linux.intel.com> <20191105231316.GE23297@linux.intel.com> In-Reply-To: <20191105231316.GE23297@linux.intel.com> From: Dan Williams Date: Tue, 5 Nov 2019 15:30:00 -0800 Message-ID: Subject: Re: [PATCH v1 03/10] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes To: Sean Christopherson Cc: David Hildenbrand , Linux Kernel Mailing List , Linux MM , Michal Hocko , Andrew Morton , kvm-ppc@vger.kernel.org, linuxppc-dev , KVM list , linux-hyperv@vger.kernel.org, devel@driverdev.osuosl.org, xen-devel , X86 ML , Alexander Duyck , Alexander Duyck , Alex Williamson , Allison Randal , Andy Lutomirski , "Aneesh Kumar K.V" , Anshuman Khandual , Anthony Yznaga , Benjamin Herrenschmidt , Borislav Petkov , Boris Ostrovsky , Christophe Leroy , Cornelia Huck , Dave Hansen , Haiyang Zhang , "H. Peter Anvin" , Ingo Molnar , "Isaac J. Manjarres" , Jim Mattson , Joerg Roedel , Johannes Weiner , Juergen Gross , KarimAllah Ahmed , Kees Cook , "K. Y. Srinivasan" , "Matthew Wilcox (Oracle)" , Matt Sickler , Mel Gorman , Michael Ellerman , Michal Hocko , Mike Rapoport , Mike Rapoport , Nicholas Piggin , Oscar Salvador , Paolo Bonzini , Paul Mackerras , Paul Mackerras , Pavel Tatashin , Pavel Tatashin , Peter Zijlstra , Qian Cai , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , Sasha Levin , Stefano Stabellini , Stephen Hemminger , Thomas Gleixner , Vitaly Kuznetsov , Vlastimil Babka , Wanpeng Li , YueHaibing , Adam Borowski Content-Type: text/plain; charset="UTF-8" X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Nov 5, 2019 at 3:13 PM Sean Christopherson wrote: > > On Tue, Nov 05, 2019 at 03:02:40PM -0800, Dan Williams wrote: > > On Tue, Nov 5, 2019 at 12:31 PM David Hildenbrand wrote: > > > > The scarier code (for me) is transparent_hugepage_adjust() and > > > > kvm_mmu_zap_collapsible_spte(), as I don't at all understand the > > > > interaction between THP and _PAGE_DEVMAP. > > > > > > The x86 KVM MMU code is one of the ugliest code I know (sorry, but it > > > had to be said :/ ). Luckily, this should be independent of the > > > PG_reserved thingy AFAIKs. > > > > Both transparent_hugepage_adjust() and kvm_mmu_zap_collapsible_spte() > > are honoring kvm_is_reserved_pfn(), so again I'm missing where the > > page count gets mismanaged and leads to the reported hang. > > When mapping pages into the guest, KVM gets the page via gup(), which > increments the page count for ZONE_DEVICE pages. But KVM puts the page > using kvm_release_pfn_clean(), which skips put_page() if PageReserved() > and so never puts its reference to ZONE_DEVICE pages. Oh, yeah, that's busted. > My transparent_hugepage_adjust() and kvm_mmu_zap_collapsible_spte() > comments were for a post-patch/series scenario wheren PageReserved() is > no longer true for ZONE_DEVICE pages. Ah, ok, for that David is preserving kvm_is_reserved_pfn() returning true for ZONE_DEVICE because pfn_to_online_page() will fail for ZONE_DEVICE.