linux-kernel - Re: [PATCH v1 5/7] mm: introduce page_offline_(begin|end|freeze|unfreeze) to synchronize setting PageOffline()

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Message-ID: <4aa55978-c224-7ead-f00d-df1a6c3dfda4@redhat.com>
Date:   Mon, 3 May 2021 10:11:29 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Mike Rapoport <rppt@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Alexey Dobriyan <adobriyan@...il.com>,
        "Matthew Wilcox (Oracle)" <willy@...radead.org>,
        Oscar Salvador <osalvador@...e.de>,
        Michal Hocko <mhocko@...e.com>, Roman Gushchin <guro@...com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Steven Price <steven.price@....com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Aili Yao <yaoaili@...gsoft.com>, Jiri Bohac <jbohac@...e.cz>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>,
        Naoya Horiguchi <naoya.horiguchi@....com>,
        linux-hyperv@...r.kernel.org,
        virtualization@...ts.linux-foundation.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v1 5/7] mm: introduce
 page_offline_(begin|end|freeze|unfreeze) to synchronize setting PageOffline()

On 02.05.21 08:33, Mike Rapoport wrote:
> On Thu, Apr 29, 2021 at 02:25:17PM +0200, David Hildenbrand wrote:
>> A driver might set a page logically offline -- PageOffline() -- and
>> turn the page inaccessible in the hypervisor; after that, access to page
>> content can be fatal. One example is virtio-mem; while unplugged memory
>> -- marked as PageOffline() can currently be read in the hypervisor, this
>> will no longer be the case in the future; for example, when having
>> a virtio-mem device backed by huge pages in the hypervisor.
>>
>> Some special PFN walkers -- i.e., /proc/kcore -- read content of random
>> pages after checking PageOffline(); however, these PFN walkers can race
>> with drivers that set PageOffline().
>>
>> Let's introduce page_offline_(begin|end|freeze|unfreeze) for
> 
> Bikeshed: freeze|thaw?
>

Sure :)


-- 
Thanks,

David / dhildenb