From: Oscar Salvador <osalvador@suse.de>
To: David Hildenbrand <david@redhat.com>
Cc: linux-kernel@vger.kernel.org,
Andrew Morton <akpm@linux-foundation.org>,
"Michael S. Tsirkin" <mst@redhat.com>,
Jason Wang <jasowang@redhat.com>,
Alexey Dobriyan <adobriyan@gmail.com>,
Mike Rapoport <rppt@kernel.org>,
"Matthew Wilcox (Oracle)" <willy@infradead.org>,
Michal Hocko <mhocko@suse.com>, Roman Gushchin <guro@fb.com>,
Alex Shi <alex.shi@linux.alibaba.com>,
Steven Price <steven.price@arm.com>,
Mike Kravetz <mike.kravetz@oracle.com>,
Aili Yao <yaoaili@kingsoft.com>, Jiri Bohac <jbohac@suse.cz>,
"K. Y. Srinivasan" <kys@microsoft.com>,
Haiyang Zhang <haiyangz@microsoft.com>,
Stephen Hemminger <sthemmin@microsoft.com>,
Wei Liu <wei.liu@kernel.org>,
Naoya Horiguchi <naoya.horiguchi@nec.com>,
linux-hyperv@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-fsdevel@vger.kernel.org, linux-mm@kvack.org
Subject: Re: [PATCH v2 4/6] mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline()
Date: Tue, 25 May 2021 10:16:26 +0200 [thread overview]
Message-ID: <20210525081626.GB3300@linux> (raw)
In-Reply-To: <20210514172247.176750-5-david@redhat.com>
On Fri, May 14, 2021 at 07:22:45PM +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|thaw) for
> synchronizing.
>
> page_offline_freeze()/page_offline_thaw() allows for a subsystem to
> synchronize with such drivers, achieving that a page cannot be set
> PageOffline() while frozen.
>
> page_offline_begin()/page_offline_end() is used by drivers that care about
> such races when setting a page PageOffline().
>
> For simplicity, use a rwsem for now; neither drivers nor users are
> performance sensitive.
>
> Acked-by: Michal Hocko <mhocko@suse.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
--
Oscar Salvador
SUSE L3
next prev parent reply other threads:[~2021-05-25 8:16 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-14 17:22 [PATCH v2 0/6] fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages David Hildenbrand
2021-05-14 17:22 ` [PATCH v2 1/6] fs/proc/kcore: drop KCORE_REMAP and KCORE_OTHER David Hildenbrand
2021-05-14 17:22 ` [PATCH v2 2/6] fs/proc/kcore: pfn_is_ram check only applies to KCORE_RAM David Hildenbrand
2021-05-14 17:22 ` [PATCH v2 3/6] fs/proc/kcore: don't read offline sections, logically offline pages and hwpoisoned pages David Hildenbrand
2021-05-25 8:09 ` Oscar Salvador
2021-05-14 17:22 ` [PATCH v2 4/6] mm: introduce page_offline_(begin|end|freeze|thaw) to synchronize setting PageOffline() David Hildenbrand
2021-05-17 6:43 ` Mike Rapoport
2021-05-17 15:18 ` David Hildenbrand
2021-05-25 8:16 ` Oscar Salvador [this message]
2021-05-14 17:22 ` [PATCH v2 5/6] virtio-mem: use page_offline_(start|end) when " David Hildenbrand
2021-05-17 6:43 ` Mike Rapoport
2021-05-25 8:20 ` Oscar Salvador
2021-05-14 17:22 ` [PATCH v2 6/6] fs/proc/kcore: use page_offline_(freeze|thaw) David Hildenbrand
2021-05-17 6:44 ` Mike Rapoport
2021-05-25 8:21 ` Oscar Salvador
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