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=-6.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS 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 8C8A7C5DF60 for ; Fri, 8 Nov 2019 18:29:20 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 2C80221848 for ; Fri, 8 Nov 2019 18:29:20 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=intel-com.20150623.gappssmtp.com header.i=@intel-com.20150623.gappssmtp.com header.b="1d0D3cRq" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2C80221848 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id A5DD46B0007; Fri, 8 Nov 2019 13:29:19 -0500 (EST) Received: by kanga.kvack.org (Postfix, from userid 40) id A0FB76B0008; Fri, 8 Nov 2019 13:29:19 -0500 (EST) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 8FCFD6B000A; Fri, 8 Nov 2019 13:29:19 -0500 (EST) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0015.hostedemail.com [216.40.44.15]) by kanga.kvack.org (Postfix) with ESMTP id 76EE26B0007 for ; Fri, 8 Nov 2019 13:29:19 -0500 (EST) Received: from smtpin17.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay04.hostedemail.com (Postfix) with SMTP id 2039940F4 for ; Fri, 8 Nov 2019 18:29:19 +0000 (UTC) X-FDA: 76133947638.17.coat72_6e58e0cf2a911 X-HE-Tag: coat72_6e58e0cf2a911 X-Filterd-Recvd-Size: 11544 Received: from mail-oi1-f196.google.com (mail-oi1-f196.google.com [209.85.167.196]) by imf22.hostedemail.com (Postfix) with ESMTP for ; Fri, 8 Nov 2019 18:29:18 +0000 (UTC) Received: by mail-oi1-f196.google.com with SMTP id 22so6091231oip.7 for ; Fri, 08 Nov 2019 10:29:17 -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:content-transfer-encoding; bh=yngiQYr/7F6QKuY7vN6LC1DaelX21SW6WtIezPVX1cs=; b=1d0D3cRq9YmW+1yK/RE0DJ/UkPslFK9ZAtUlZvAmKEittn+5P29MLqMMstbFi6jxrj Ns+iC+3lEfqovG/2PeSjS3wVktY00J2VZo7ibdEFMbFztKpI1VGkrK4Z6kX7z5EzrUom bSTVU2MgPfHTpWNd+xSEyU8xK4V1kffBbeLvkwqwFJj8qpE4mYF7AJRg+qxJndVPhMij YrZFUYzgb9mQnIKiWG8Byr1keTk4OMIwDas2SXSrk7iFZyyCWOQnqkn+P1k9XRe9xeBr mL6RRd4GY0O+nfHuYs60Bo8b9/FTK1kKLaz6x7EetX7XNninU7M5eC1ph48V7wcf59eX ybUw== 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:content-transfer-encoding; bh=yngiQYr/7F6QKuY7vN6LC1DaelX21SW6WtIezPVX1cs=; b=rCFCLOsCIexNDGaGQUZYCiB1GtXwwh6R796+SB3khWDhkazyMPmE99YkRVBgf3P3Qb dhFY+KzYchbG8PF5PXTN2UfZJgr7Lx2OK2jZBIRyWRrzx5mjBkQP4SAFJjijRvr1Eruw 1lwPT+UTsj4gHS2a9ESiChqAxYllbMf/o1Y8ZRMU3cFXgnrihw3txUy78hl0QVBdmvj9 iIvo8RzNGMdGfu/7TD19dr7vhXAwdY7XoLM+emB/Opb8NZ0w0m96xsJlD3Xak0wi1VLh KxQZY1RruHYkivfjZFtD1VQtEoNAoE80f2anixnjINDi03MlaG6qSqbQPzMZnWKq0+Sh ndmA== X-Gm-Message-State: APjAAAU17BqtDsD5PA11UuApGDvPel1eC+yKy0UnY3Hi6lEFIqcnVtrC pXkmNYMrh2H4dgoNAYj2qHnXjfx9TcbLsWoAJS3jdg== X-Google-Smtp-Source: APXvYqyW1emHhRBKHxxXAScz16mwYUdha6EWMf/eNJ6eW2bb1Fqoly3wylgSEbuygHP3+YkWg3AvDZQxJt18zmA6EEU= X-Received: by 2002:aca:1910:: with SMTP id l16mr10558260oii.73.1573237757087; Fri, 08 Nov 2019 10:29:17 -0800 (PST) MIME-Version: 1.0 References: <0eb001e0-bb26-59bb-c514-d2f8a86a7eab@redhat.com> <931cb766-c3fb-8093-d8d0-144d328e69fc@redhat.com> In-Reply-To: <931cb766-c3fb-8093-d8d0-144d328e69fc@redhat.com> From: Dan Williams Date: Fri, 8 Nov 2019 10:29:06 -0800 Message-ID: Subject: Re: [PATCH v1 04/10] vfio/type1: Prepare is_invalid_reserved_pfn() for PG_reserved changes To: David Hildenbrand 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 Content-Type: text/plain; charset="UTF-8" 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 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_hotplu= g.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. 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.