linuxppc-dev.lists.ozlabs.org archive mirror
 help / color / mirror / Atom feed
From: David Hildenbrand <david@redhat.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>,
	"Pavel Tatashin" <pavel.tatashin@microsoft.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>,
	"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,
	"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>,
	"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>,
	"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>,
	"Mel Gorman" <mgorman@techsingularity.net>,
	"Adam Borowski" <kilobyte@angband.pl>,
	"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 03/10] KVM: Prepare kvm_is_reserved_pfn() for PG_reserved changes
Date: Tue, 5 Nov 2019 10:49:10 +0100	[thread overview]
Message-ID: <01adb4cb-6092-638c-0bab-e61322be7cf5@redhat.com> (raw)
In-Reply-To: <bbe59155-24ae-f229-e182-107730423c47@redhat.com>

On 05.11.19 10:17, David Hildenbrand wrote:
> On 05.11.19 05:38, Dan Williams wrote:
>> On Thu, Oct 24, 2019 at 5:11 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 kvm_is_reserved_pfn() to make sure the function produces the
>>> same result once we stop setting ZONE_DEVICE pages PG_reserved.
>>>
>>> Cc: Paolo Bonzini <pbonzini@redhat.com>
>>> Cc: "Radim Krčmář" <rkrcmar@redhat.com>
>>> Cc: Michal Hocko <mhocko@kernel.org>
>>> Cc: Dan Williams <dan.j.williams@intel.com>
>>> Cc: KarimAllah Ahmed <karahmed@amazon.de>
>>> Signed-off-by: David Hildenbrand <david@redhat.com>
>>> ---
>>>    virt/kvm/kvm_main.c | 10 ++++++++--
>>>    1 file changed, 8 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
>>> index e9eb666eb6e8..9d18cc67d124 100644
>>> --- a/virt/kvm/kvm_main.c
>>> +++ b/virt/kvm/kvm_main.c
>>> @@ -151,9 +151,15 @@ __weak int kvm_arch_mmu_notifier_invalidate_range(struct kvm *kvm,
>>>
>>>    bool kvm_is_reserved_pfn(kvm_pfn_t pfn)
>>>    {
>>> -       if (pfn_valid(pfn))
>>> -               return PageReserved(pfn_to_page(pfn));
>>> +       struct page *page = pfn_to_online_page(pfn);
>>>
>>> +       /*
>>> +        * We treat any pages that are not online (not managed by the buddy)
>>> +        * as reserved - this includes ZONE_DEVICE pages and pages without
>>> +        * a memmap (e.g., mapped via /dev/mem).
>>> +        */
>>> +       if (page)
>>> +               return PageReserved(page);
>>>           return true;
>>>    }
>>
>> So after this all the pfn_valid() usage in kvm_main.c is replaced with
>> pfn_to_online_page()? Looks correct to me.
>>
>> However, I'm worried that kvm is taking reference on ZONE_DEVICE pages
>> through some other path resulting in this:
>>
>>       https://lore.kernel.org/linux-nvdimm/20190919154708.GA24650@angband.pl/
>>
>> I'll see if this patch set modulates or maintains that failure mode.
>>
> 
> I'd assume that the behavior is unchanged. Ithink we get a reference to
> these ZONE_DEVICE pages via __get_user_pages_fast() and friends in
> hva_to_pfn_fast() and friends in virt/kvm/kvm_main.c
> 

I think I know what's going wrong:

Pages that are pinned via gfn_to_pfn() and friends take a references, 
however are often released via 
kvm_release_pfn_clean()/kvm_release_pfn_dirty()/kvm_release_page_clean()...


E.g., in arch/x86/kvm/x86.c:reexecute_instruction()

...
pfn = gfn_to_pfn(vcpu->kvm, gpa_to_gfn(gpa));
...
kvm_release_pfn_clean(pfn);



void kvm_release_pfn_clean(kvm_pfn_t pfn)
{
	if (!is_error_noslot_pfn(pfn) && !kvm_is_reserved_pfn(pfn))
		put_page(pfn_to_page(pfn));
}

This function makes perfect sense as the counterpart for kvm_get_pfn():

void kvm_get_pfn(kvm_pfn_t pfn)
{
	if (!kvm_is_reserved_pfn(pfn))
		get_page(pfn_to_page(pfn));
}


As all ZONE_DEVICE pages are currently reserved, pages pinned via 
gfn_to_pfn() and friends will often not see a put_page() AFAIKS.

Now, my patch does not change that, the result of 
kvm_is_reserved_pfn(pfn) will be unchanged. A proper fix for that would 
probably be

a) To drop the reference to ZONE_DEVICE pages in gfn_to_pfn() and 
friends, after you successfully pinned the pages. (not sure if that's 
the right thing to do but you're the expert)

b) To not use kvm_release_pfn_clean() and friends on pages that were 
definitely pinned.

-- 

Thanks,

David / dhildenb


  reply	other threads:[~2019-11-05 10:54 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 [this message]
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
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 publicly 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=01adb4cb-6092-638c-0bab-e61322be7cf5@redhat.com \
    --to=david@redhat.com \
    --cc=Matt.Sickler@daktronics.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=boris.ostrovsky@oracle.com \
    --cc=bp@alien8.de \
    --cc=cai@lca.pw \
    --cc=cohuck@redhat.com \
    --cc=dan.j.williams@intel.com \
    --cc=dave.hansen@linux.intel.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=kilobyte@angband.pl \
    --cc=kvm-ppc@vger.kernel.org \
    --cc=kvm@vger.kernel.org \
    --cc=kys@microsoft.com \
    --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=npiggin@gmail.com \
    --cc=osalvador@suse.de \
    --cc=pasha.tatashin@soleen.com \
    --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
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).