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=-8.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 9C912C17441 for ; Fri, 8 Nov 2019 23:02:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 4C4C320865 for ; Fri, 8 Nov 2019 23:02:12 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=redhat.com header.i=@redhat.com header.b="eNJUQUoY" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 4C4C320865 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=redhat.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id D7E176B0003; Fri, 8 Nov 2019 18:02:11 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id D2EFB6B0006; Fri, 8 Nov 2019 18:02:11 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id C1EF56B0007; Fri, 8 Nov 2019 18:02:11 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0193.hostedemail.com [216.40.44.193]) by kanga.kvack.org (Postfix) with ESMTP id A9B206B0003 for ; Fri, 8 Nov 2019 18:02:11 -0500 (EST) Received: from smtpin09.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay05.hostedemail.com (Postfix) with SMTP id 54002181AEF10 for ; Fri, 8 Nov 2019 23:02:11 +0000 (UTC) X-FDA: 76134635262.09.rub46_130a9c37cf23f X-HE-Tag: rub46_130a9c37cf23f X-Filterd-Recvd-Size: 11597 Received: from us-smtp-1.mimecast.com (us-smtp-delivery-1.mimecast.com [207.211.31.120]) by imf25.hostedemail.com (Postfix) with ESMTP for ; Fri, 8 Nov 2019 23:02:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1573254130; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=K2NCDVuV0/kQDSAATePRuSEbIDA12CWhvMclhMdQSdE=; b=eNJUQUoY4S0Gx1y2hxY0Ge3q3BMba3jiuC85aQnckle56Cmtla8mypw9mLxViNcH+5Rw8L BLs2MluwGOnyZQQUtd56cOhWXqLydruk+iFCIQqCQUWH9/Y5OrxWhQJIRvcq77RrABSR0b /2UhvAe0hJ+JVIIGK2doqXugb29V9TY= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-345-9VDzBxTDMAmNaGguUgi4aw-1; Fri, 08 Nov 2019 18:02:08 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id EE3651005500; Fri, 8 Nov 2019 23:02:01 +0000 (UTC) Received: from [10.36.116.65] (ovpn-116-65.ams2.redhat.com [10.36.116.65]) by smtp.corp.redhat.com (Postfix) with ESMTP id 0FA3A100EBA4; Fri, 8 Nov 2019 23:01:41 +0000 (UTC) Subject: Re: [PATCH v1 04/10] vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes To: Dan Williams Cc: Michal Hocko , Linux Kernel Mailing List , Linux MM , 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 , Sean Christopherson , Stefano Stabellini , Stephen Hemminger , Thomas Gleixner , Vitaly Kuznetsov , Vlastimil Babka , Wanpeng Li , YueHaibing References: <0eb001e0-bb26-59bb-c514-d2f8a86a7eab@redhat.com> <931cb766-c3fb-8093-d8d0-144d328e69fc@redhat.com> From: David Hildenbrand Organization: Red Hat GmbH Message-ID: <5413f9c3-dc6a-d8ba-3777-41e99714af3d@redhat.com> Date: Sat, 9 Nov 2019 00:01:40 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.1 MIME-Version: 1.0 In-Reply-To: Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.22 X-MC-Unique: 9VDzBxTDMAmNaGguUgi4aw-1 X-Mimecast-Spam-Score: 0 Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: quoted-printable 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 08.11.19 19:29, Dan Williams wrote: > On Fri, Nov 8, 2019 at 2:22 AM David Hildenbrand 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 wr= ote: >>>>> >>>>> On 07.11.19 19:22, David Hildenbrand wrote: >>>>>> >>>>>> >>>>>>> Am 07.11.2019 um 16:40 schrieb Dan Williams : >>>>>>> >>>>>>> =EF=BB=BFOn Thu, Oct 24, 2019 at 5:12 AM David Hildenbrand wrote: >>>>>>>> >>>>>>>> Right now, ZONE_DEVICE memory is always set PG_reserved. We want t= o >>>>>>>> change that. >>>>>>>> >>>>>>>> KVM has this weird use case that you can map anything from /dev/me= m >>>>>>>> into the guest. pfn_valid() is not a reliable check whether the me= mmap >>>>>>>> was initialized and can be touched. pfn_to_online_page() makes sur= e >>>>>>>> that we have an initialized memmap (and don't have ZONE_DEVICE mem= ory). >>>>>>>> >>>>>>>> Rewrite is_invalid_reserved_pfn() similar to kvm_is_reserved_pfn()= to make >>>>>>>> sure the function produces the same result once we stop setting ZO= NE_DEVICE >>>>>>>> pages PG_reserved. >>>>>>>> >>>>>>>> Cc: Alex Williamson >>>>>>>> Cc: Cornelia Huck >>>>>>>> Signed-off-by: David Hildenbrand >>>>>>>> --- >>>>>>>> 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_i= ommu_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 *dm= a, 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 =3D 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 intro= duced subsection support that I don=E2=80=99t want to have ZONE_DEVICE mixe= d with online pages in a section. Having memory block devices that partiall= y span ZONE_DEVICE would be ... really weird. With something like pfn_activ= e() - 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, ca= n >>>>> we have ZONE_DEVICE falling into a memory block (with holes)? I somew= hat >>>>> 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 o= f >>> the section are basically "holes" and not memory. >>> >>> Yes, it is a real bug that ZONE_DEVICE pages fall into sections that ar= e >>> 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 fallin= g >>> 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_hotpl= ug.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 =3D pfn_to_page(___pfn); \ >> + if (unlikely(___page && is_zone_device_page(___page))) \ >> + ___page =3D 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. >=20 > 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. >=20 Fair enough, but at least in what I proposed for pfn_active(), this=20 check would exist in pfn_to_online_page() in a similar way - and it is=20 certainly easier to backport. But yeah, triggering this might not be easy. --=20 Thanks, David / dhildenb