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From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: linux-hyperv@vger.kernel.org, "Michal Hocko" <mhocko@suse.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"KVM list" <kvm@vger.kernel.org>,
	"David Hildenbrand" <david@redhat.com>,
	"KarimAllah Ahmed" <karahmed@amazon.de>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Alexander Duyck" <alexander.duyck@gmail.com>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Pavel Tatashin" <pavel.tatashin@microsoft.com>,
	"Paul Mackerras" <paulus@samba.org>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
	"K. Y. Srinivasan" <kys@microsoft.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Kees Cook" <keescook@chromium.org>,
	devel@driverdev.osuosl.org,
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	"Ingo Molnar" <mingo@redhat.com>,
	"Vlastimil Babka" <vbabka@suse.cz>,
	"Anthony Yznaga" <anthony.yznaga@oracle.com>,
	"Oscar Salvador" <osalvador@suse.de>,
	"Isaac J. Manjarres" <isaacm@codeaurora.org>,
	"Matt Sickler" <Matt.Sickler@daktronics.com>,
	"Juergen Gross" <jgross@suse.com>,
	"Anshuman Khandual" <anshuman.khandual@arm.com>,
	"Haiyang Zhang" <haiyangz@microsoft.com>,
	"Sasha Levin" <sashal@kernel.org>,
	kvm-ppc@vger.kernel.org, "Qian Cai" <cai@lca.pw>,
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	xen-devel <xen-devel@lists.xenproject.org>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Vitaly Kuznetsov" <vkuznets@redhat.com>,
	"Allison Randal" <allison@lohutok.net>,
	"Jim Mattson" <jmattson@google.com>,
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	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v1 03/10] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes
Date: Tue, 5 Nov 2019 15:13:16 -0800	[thread overview]
Message-ID: <20191105231316.GE23297@linux.intel.com> (raw)
In-Reply-To: <CAPcyv4htPCeui80fOOno+7AFo3V-=VEiWkAv8j+-Kkad+UnFGQ@mail.gmail.com>

On Tue, Nov 05, 2019 at 03:02:40PM -0800, Dan Williams wrote:
> On Tue, Nov 5, 2019 at 12:31 PM David Hildenbrand <david@redhat.com> 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.

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.

  reply	other threads:[~2019-11-06  0:09 UTC|newest]

Thread overview: 43+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-24 12:09 [PATCH v1 00/10] mm: Don't mark hotplugged pages PG_reserved (including ZONE_DEVICE) David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 01/10] mm/memory_hotplug: Don't allow to online/offline memory blocks with holes David Hildenbrand
2019-11-05  1:30   ` Dan Williams
2019-11-05  9:31     ` David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 02/10] KVM: x86/mmu: Prepare kvm_is_mmio_pfn() for PG_reserved changes David Hildenbrand
2019-11-05  1:37   ` Dan Williams
2019-11-05 11:09     ` David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 03/10] KVM: Prepare kvm_is_reserved_pfn() " David Hildenbrand
2019-11-05  4:38   ` Dan Williams
2019-11-05  9:17     ` David Hildenbrand
2019-11-05  9:49       ` David Hildenbrand
2019-11-05 10:02         ` David Hildenbrand
2019-11-05 16:00           ` Sean Christopherson
2019-11-05 20:30             ` David Hildenbrand
2019-11-05 22:22               ` Sean Christopherson
2019-11-05 23:02               ` Dan Williams
2019-11-05 23:13                 ` Sean Christopherson [this message]
2019-11-05 23:30                   ` Dan Williams
2019-11-05 23:42                     ` Sean Christopherson
2019-11-05 23:43                     ` Dan Williams
2019-11-06  0:03                       ` Sean Christopherson
2019-11-06  0:08                         ` Dan Williams
2019-11-06  6:56                           ` David Hildenbrand
2019-11-06 16:09                             ` Sean Christopherson
2019-10-24 12:09 ` [PATCH v1 04/10] vfio/type1: Prepare is_invalid_reserved_pfn() " David Hildenbrand
2019-11-07 15:40   ` Dan Williams
2019-11-07 18:22     ` David Hildenbrand
2019-11-07 22:07       ` David Hildenbrand
2019-11-08  5:09         ` Dan Williams
2019-11-08  7:14           ` David Hildenbrand
2019-11-08 10:21             ` David Hildenbrand
2019-11-08 18:29               ` Dan Williams
2019-11-08 23:01                 ` David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 05/10] powerpc/book3s: Prepare kvmppc_book3s_instantiate_page() " David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 06/10] powerpc/64s: Prepare hash_page_do_lazy_icache() " David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 07/10] powerpc/mm: Prepare maybe_pte_to_page() " David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 08/10] x86/mm: Prepare __ioremap_check_ram() " David Hildenbrand
2019-10-24 12:09 ` [PATCH v1 09/10] mm/memory_hotplug: Don't mark pages PG_reserved when initializing the memmap David Hildenbrand
2019-11-04 22:44   ` Boris Ostrovsky
2019-11-05 10:18     ` David Hildenbrand
2019-11-05 16:06       ` Boris Ostrovsky
2019-10-24 12:09 ` [PATCH v1 10/10] mm/usercopy.c: Update comment in check_page_span() regarding ZONE_DEVICE David Hildenbrand
2019-11-01 19:24 ` [PATCH v1 00/10] mm: Don't mark hotplugged pages PG_reserved (including ZONE_DEVICE) David Hildenbrand

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