DriverDev-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Dan Williams <dan.j.williams@intel.com>
To: David Hildenbrand <david@redhat.com>
Cc: linux-hyperv@vger.kernel.org, "Michal Hocko" <mhocko@suse.com>,
	"Radim Krčmář" <rkrcmar@redhat.com>,
	"KVM list" <kvm@vger.kernel.org>,
	"Pavel Tatashin" <pavel.tatashin@microsoft.com>,
	"KarimAllah Ahmed" <karahmed@amazon.de>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Alexander Duyck" <alexander.duyck@gmail.com>,
	"Michal Hocko" <mhocko@kernel.org>,
	"Paul Mackerras" <paulus@ozlabs.org>,
	"Linux MM" <linux-mm@kvack.org>,
	"Paul Mackerras" <paulus@samba.org>,
	"Michael Ellerman" <mpe@ellerman.id.au>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	"Alexander Duyck" <alexander.h.duyck@linux.intel.com>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Kees Cook" <keescook@chromium.org>,
	devel@driverdev.osuosl.org,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Stephen Hemminger" <sthemmin@microsoft.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>,
	"Joerg Roedel" <joro@8bytes.org>, "X86 ML" <x86@kernel.org>,
	YueHaibing <yuehaibing@huawei.com>,
	"Matthew Wilcox (Oracle)" <willy@infradead.org>,
	"Mike Rapoport" <rppt@linux.ibm.com>,
	"Peter Zijlstra" <peterz@infradead.org>,
	"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>,
	"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>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Mike Rapoport" <rppt@linux.vnet.ibm.com>,
	"Borislav Petkov" <bp@alien8.de>,
	"Nicholas Piggin" <npiggin@gmail.com>,
	"Andy Lutomirski" <luto@kernel.org>,
	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>,
	"Christophe Leroy" <christophe.leroy@c-s.fr>,
	"Mel Gorman" <mgorman@techsingularity.net>,
	"Cornelia Huck" <cohuck@redhat.com>,
	"Pavel Tatashin" <pasha.tatashin@soleen.com>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Johannes Weiner" <hannes@cmpxchg.org>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Andrew Morton" <akpm@linux-foundation.org>,
	linuxppc-dev <linuxppc-dev@lists.ozlabs.org>
Subject: Re: [PATCH v1 04/10] vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes
Date: Fri, 8 Nov 2019 10:29:06 -0800
Message-ID: <CAPcyv4ivq=EPUePXiX2ErcVyF7+dV9Yv215Oue7X_Y2X_Jfw8Q@mail.gmail.com> (raw)
In-Reply-To: <931cb766-c3fb-8093-d8d0-144d328e69fc@redhat.com>

On Fri, Nov 8, 2019 at 2:22 AM David Hildenbrand <david@redhat.com> wrote:
>
> On 08.11.19 08:14, David Hildenbrand wrote:
> > On 08.11.19 06:09, Dan Williams wrote:
> >> On Thu, Nov 7, 2019 at 2:07 PM David Hildenbrand <david@redhat.com> wrote:
> >>>
> >>> On 07.11.19 19:22, David Hildenbrand wrote:
> >>>>
> >>>>
> >>>>> Am 07.11.2019 um 16:40 schrieb Dan Williams <dan.j.williams@intel.com>:
> >>>>>
> >>>>> On Thu, Oct 24, 2019 at 5:12 AM David Hildenbrand <david@redhat.com> wrote:
> >>>>>>
> >>>>>> Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
> >>>>>> change that.
> >>>>>>
> >>>>>> KVM has this weird use case that you can map anything from /dev/mem
> >>>>>> into the guest. pfn_valid() is not a reliable check whether the memmap
> >>>>>> was initialized and can be touched. pfn_to_online_page() makes sure
> >>>>>> that we have an initialized memmap (and don't have ZONE_DEVICE memory).
> >>>>>>
> >>>>>> Rewrite is_invalid_reserved_pfn() similar to kvm_is_reserved_pfn() to make
> >>>>>> sure the function produces the same result once we stop setting ZONE_DEVICE
> >>>>>> pages PG_reserved.
> >>>>>>
> >>>>>> Cc: Alex Williamson <alex.williamson@redhat.com>
> >>>>>> Cc: Cornelia Huck <cohuck@redhat.com>
> >>>>>> Signed-off-by: David Hildenbrand <david@redhat.com>
> >>>>>> ---
> >>>>>> drivers/vfio/vfio_iommu_type1.c | 10 ++++++++--
> >>>>>> 1 file changed, 8 insertions(+), 2 deletions(-)
> >>>>>>
> >>>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
> >>>>>> index 2ada8e6cdb88..f8ce8c408ba8 100644
> >>>>>> --- a/drivers/vfio/vfio_iommu_type1.c
> >>>>>> +++ b/drivers/vfio/vfio_iommu_type1.c
> >>>>>> @@ -299,9 +299,15 @@ static int vfio_lock_acct(struct vfio_dma *dma, long npage, bool async)
> >>>>>>     */
> >>>>>> static bool is_invalid_reserved_pfn(unsigned long pfn)
> >>>>>> {
> >>>>>> -       if (pfn_valid(pfn))
> >>>>>> -               return PageReserved(pfn_to_page(pfn));
> >>>>>> +       struct page *page = pfn_to_online_page(pfn);
> >>>>>
> >>>>> Ugh, I just realized this is not a safe conversion until
> >>>>> pfn_to_online_page() is moved over to subsection granularity. As it
> >>>>> stands it will return true for any ZONE_DEVICE pages that share a
> >>>>> section with boot memory.
> >>>>
> >>>> That should not happen right now and I commented back when you introduced subsection support that I don’t want to have ZONE_DEVICE mixed with online pages in a section. Having memory block devices that partially span ZONE_DEVICE would be ... really weird. With something like pfn_active() - as discussed - we could at least make this check work - but I am not sure if we really want to go down that path. In the worst case, some MB of RAM are lost ... I guess this needs more thought.
> >>>>
> >>>
> >>> I just realized the "boot memory" part. Is that a real thing? IOW, can
> >>> we have ZONE_DEVICE falling into a memory block (with holes)? I somewhat
> >>> have doubts that this would work ...
> >>
> >> One of the real world failure cases that started the subsection effect
> >> is that Persistent Memory collides with System RAM on a 64MB boundary
> >> on shipping platforms. System RAM ends on a 64MB boundary and due to a
> >> lack of memory controller resources PMEM is mapped contiguously at the
> >> end of that boundary. Some more details in the subsection cover letter
> >> / changelogs [1] [2]. It's not sufficient to just lose some memory,
> >> that's the broken implementation that lead to the subsection work
> >> because the lost memory may change from one boot to the next and
> >> software can't reliably inject a padding that conforms to the x86
> >> 128MB section constraint.
> >
> > Thanks, I thought it was mostly for weird alignment where other parts of
> > the section are basically "holes" and not memory.
> >
> > Yes, it is a real bug that ZONE_DEVICE pages fall into sections that are
> > marked SECTION_IS_ONLINE.
> >
> >>
> >> Suffice to say I think we need your pfn_active() to get subsection
> >> granularity pfn_to_online_page() before PageReserved() can be removed.
> >
> > I agree that we have to fix this. I don't like ZONE_DEVICE pages falling
> > into memory device blocks (e.g., cannot get offlined), but I guess that
> > train is gone :) As long as it's not for memory hotplug, I can most
> > probably live with this.
> >
> > Also, I'd like to get Michals opinion on this and the pfn_active()
> > approach, but I can understand he's busy.
> >
> > This patch set can wait, I won't be working next week besides
> > reading/writing mails either way.
> >
> > Is anybody looking into the pfn_active() thingy?
> >
>
> I wonder if we should do something like this right now to fix this
> (exclude the false positive ZONE_DEVICE pages we could have within an
> online section, which was not possible before subsection hotplug):
>
> diff --git a/include/linux/memory_hotplug.h b/include/linux/memory_hotplug.h
> index 384ffb3d69ab..490a9e9358b3 100644
> --- a/include/linux/memory_hotplug.h
> +++ b/include/linux/memory_hotplug.h
> @@ -30,6 +30,8 @@ struct vmem_altmap;
>          if (___nr < NR_MEM_SECTIONS && online_section_nr(___nr) && \
>              pfn_valid_within(___pfn))                              \
>                  ___page = pfn_to_page(___pfn);                     \
> +       if (unlikely(___page && is_zone_device_page(___page)))     \
> +               ___page = NULL;                                    \
>          ___page;                                                   \
>   })
>
>
> Yeah, it's another is_zone_device_page(), but it should not be racy
> here, as we want to exclude, not include ZONE_DEVICE.
>
> I don't have time to look into this right now, unfortunately.

I don't want to band-aid without an actual bug report. I'll take a
look at a subsection-map for the online state.
_______________________________________________
devel mailing list
devel@linuxdriverproject.org
http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel

  reply index

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
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 [this message]
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to='CAPcyv4ivq=EPUePXiX2ErcVyF7+dV9Yv215Oue7X_Y2X_Jfw8Q@mail.gmail.com' \
    --to=dan.j.williams@intel.com \
    --cc=akpm@linux-foundation.org \
    --cc=alex.williamson@redhat.com \
    --cc=alexander.duyck@gmail.com \
    --cc=alexander.h.duyck@linux.intel.com \
    --cc=allison@lohutok.net \
    --cc=aneesh.kumar@linux.ibm.com \
    --cc=anshuman.khandual@arm.com \
    --cc=anthony.yznaga@oracle.com \
    --cc=benh@kernel.crashing.org \
    --cc=boris.ostrovsky@oracle.com \
    --cc=bp@alien8.de \
    --cc=cai@lca.pw \
    --cc=christophe.leroy@c-s.fr \
    --cc=cohuck@redhat.com \
    --cc=dave.hansen@linux.intel.com \
    --cc=david@redhat.com \
    --cc=devel@driverdev.osuosl.org \
    --cc=haiyangz@microsoft.com \
    --cc=hannes@cmpxchg.org \
    --cc=hpa@zytor.com \
    --cc=isaacm@codeaurora.org \
    --cc=jgross@suse.com \
    --cc=jmattson@google.com \
    --cc=joro@8bytes.org \
    --cc=karahmed@amazon.de \
    --cc=keescook@chromium.org \
    --cc=kvm-ppc@vger.kernel.org \
    --cc=kvm@vger.kernel.org \
    --cc=linux-hyperv@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=linux-mm@kvack.org \
    --cc=linuxppc-dev@lists.ozlabs.org \
    --cc=luto@kernel.org \
    --cc=mgorman@techsingularity.net \
    --cc=mhocko@kernel.org \
    --cc=mhocko@suse.com \
    --cc=mingo@redhat.com \
    --cc=mpe@ellerman.id.au \
    --cc=npiggin@gmail.com \
    --cc=osalvador@suse.de \
    --cc=pasha.tatashin@soleen.com \
    --cc=paulus@ozlabs.org \
    --cc=paulus@samba.org \
    --cc=pavel.tatashin@microsoft.com \
    --cc=pbonzini@redhat.com \
    --cc=peterz@infradead.org \
    --cc=rkrcmar@redhat.com \
    --cc=rppt@linux.ibm.com \
    --cc=rppt@linux.vnet.ibm.com \
    --cc=sashal@kernel.org \
    --cc=sean.j.christopherson@intel.com \
    --cc=sstabellini@kernel.org \
    --cc=sthemmin@microsoft.com \
    --cc=tglx@linutronix.de \
    --cc=vbabka@suse.cz \
    --cc=vkuznets@redhat.com \
    --cc=wanpengli@tencent.com \
    --cc=willy@infradead.org \
    --cc=x86@kernel.org \
    --cc=xen-devel@lists.xenproject.org \
    --cc=yuehaibing@huawei.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

DriverDev-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/driverdev-devel/0 driverdev-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 driverdev-devel driverdev-devel/ https://lore.kernel.org/driverdev-devel \
		driverdev-devel@linuxdriverproject.org devel@driverdev.osuosl.org
	public-inbox-index driverdev-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.linuxdriverproject.driverdev-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git