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Tue, 5 Nov 2019 23:30:11 +0000 (UTC) X-Greylist: from auto-whitelisted by SQLgrey-1.7.6 Received: from mail-ot1-f66.google.com (mail-ot1-f66.google.com [209.85.210.66]) by fraxinus.osuosl.org (Postfix) with ESMTPS id D850585DF6 for ; Tue, 5 Nov 2019 23:30:11 +0000 (UTC) Received: by mail-ot1-f66.google.com with SMTP id z6so19243162otb.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=iZuUCiwHLr73i/qTo+yiSoMtgDIq2qWt4R7q0KpYfvqjKvSK+aFc9TClefuSnuObUx heH5P89C3z4zqnJRH7eFa7qy97xlbcN2VydIcFy8cmoNRLwckkQuWo4OaevCeu7BbHOT d+EgXEINnnuE6UAt2XWDKwlHZywvbcNQXsWAGMNxNrwcrIgENamtz1ckaR52wsGgMDKP 7DADZ2ZRQfPrcvXnCqVVRTJdFcL1tzGU+qr53O/i/VGlfYRBVLvfItHIEbrhhQleQJT+ XOynLrmZYfbx5JJ2MmdWQVCBcCW5ZO8D62qWT1q7JLkqYUc3cyHwIH3ScsrBq/tpKq1g WT+Q== X-Gm-Message-State: APjAAAW4pPQit9EbUhmms2f15ocIRfmdHY4C4v+0mYPoGKAng/SGwB6+ E4dvE6dE5XG0fz/5jPQ1L9PhPui/0TqoxCS7Zv00ag== 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 X-BeenThere: driverdev-devel@linuxdriverproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux Driver Project Developer List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-hyperv@vger.kernel.org, Michal Hocko , =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= , KVM list , David Hildenbrand , KarimAllah Ahmed , Benjamin Herrenschmidt , Dave Hansen , Alexander Duyck , Michal Hocko , Paul Mackerras , Linux MM , Pavel Tatashin , Paul Mackerras , Michael Ellerman , "H. Peter Anvin" , Wanpeng Li , Alexander Duyck , Thomas Gleixner , Kees Cook , devel@driverdev.osuosl.org, Stefano Stabellini , Stephen Hemminger , "Aneesh Kumar K.V" , Joerg Roedel , X86 ML , YueHaibing , "Matthew Wilcox \(Oracle\)" , Mike Rapoport , Peter Zijlstra , Ingo Molnar , Vlastimil Babka , Anthony Yznaga , Oscar Salvador , "Isaac J. Manjarres" , Juergen Gross , Anshuman Khandual , Haiyang Zhang , Sasha Levin , kvm-ppc@vger.kernel.org, Qian Cai , Alex Williamson , Mike Rapoport , Borislav Petkov , Nicholas Piggin , Andy Lutomirski , xen-devel , Boris Ostrovsky , Vitaly Kuznetsov , Allison Randal , Jim Mattson , Christophe Leroy , Mel Gorman , Adam Borowski , Cornelia Huck , Pavel Tatashin , Linux Kernel Mailing List , Johannes Weiner , Paolo Bonzini , Andrew Morton , linuxppc-dev Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: driverdev-devel-bounces@linuxdriverproject.org Sender: "devel" 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. _______________________________________________ devel mailing list devel@linuxdriverproject.org http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel