From: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: jack-AlSwsSmVLrQ@public.gmane.org,
kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
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darrick wong
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xiaoguangrong eric
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Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device
Date: Mon, 14 Jan 2019 02:15:40 -0500 (EST) [thread overview]
Message-ID: <942065073.64011540.1547450140670.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <20190113233820.GX6310-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
> > Until you have images (and hence host page cache) shared between
> > multiple guests. People will want to do this, because it means they
> > only need a single set of pages in host memory for executable
> > binaries rather than a set of pages per guest. Then you have
> > multiple guests being able to detect residency of the same set of
> > pages. If the guests can then, in any way, control eviction of the
> > pages from the host cache, then we have a guest-to-guest information
> > leak channel.
>
> I don't think we should ever be considering something that would allow a
> guest to evict page's from the host's pagecache [1]. The guest should
> be able to kick its own references to the host's pagecache out of its
> own pagecache, but not be able to influence whether the host or another
> guest has a read-only mapping cached.
>
> [1] Unless the guest is allowed to modify the host's file; obviously
> truncation, holepunching, etc are going to evict pages from the host's
> page cache.
This is so correct. Guest does not not evict host page cache pages directly.
In case of virtio-pmem & DAX, guest clears guest page cache exceptional entries.
Its solely decision of host to take action on the host page cache pages.
In case of virtio-pmem, guest does not modify host file directly i.e don't
perform hole punch & truncation operation directly on host file.
Thanks,
Pankaj
WARNING: multiple messages have this Message-ID (diff)
From: Pankaj Gupta <pagupta@redhat.com>
To: Matthew Wilcox <willy@infradead.org>
Cc: Dave Chinner <david@fromorbit.com>,
linux-kernel@vger.kernel.org, kvm@vger.kernel.org,
qemu-devel@nongnu.org, linux-nvdimm@ml01.01.org,
linux-fsdevel@vger.kernel.org,
virtualization@lists.linux-foundation.org,
linux-acpi@vger.kernel.org, linux-ext4@vger.kernel.org,
linux-xfs@vger.kernel.org, jack@suse.cz, stefanha@redhat.com,
dan j williams <dan.j.williams@intel.com>,
riel@surriel.com, nilal@redhat.com, kwolf@redhat.com,
pbonzini@redhat.com, zwisler@kernel.org,
vishal l verma <vishal.l.verma@intel.com>,
dave jiang <dave.jiang@intel.com>,
david@redhat.com, jmoyer@redhat.com,
xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
hch@infradead.org, mst@redhat.com, jasowang@redhat.com,
lcapitulino@redhat.com, imammedo@redhat.com, eblake@redhat.com,
tytso@mit.edu, adilger kernel <adilger.kernel@dilger.ca>,
darrick wong <darrick.wong@oracle.com>,
rjw@rjwysocki.net
Subject: Re: [PATCH v3 0/5] kvm "virtio pmem" device
Date: Mon, 14 Jan 2019 02:15:40 -0500 (EST) [thread overview]
Message-ID: <942065073.64011540.1547450140670.JavaMail.zimbra@redhat.com> (raw)
Message-ID: <20190114071540.qMIRPRhSeAPkq0JpakkzARC8s93KAD_ofwfjc0_k5LQ@z> (raw)
In-Reply-To: <20190113233820.GX6310@bombadil.infradead.org>
> > Until you have images (and hence host page cache) shared between
> > multiple guests. People will want to do this, because it means they
> > only need a single set of pages in host memory for executable
> > binaries rather than a set of pages per guest. Then you have
> > multiple guests being able to detect residency of the same set of
> > pages. If the guests can then, in any way, control eviction of the
> > pages from the host cache, then we have a guest-to-guest information
> > leak channel.
>
> I don't think we should ever be considering something that would allow a
> guest to evict page's from the host's pagecache [1]. The guest should
> be able to kick its own references to the host's pagecache out of its
> own pagecache, but not be able to influence whether the host or another
> guest has a read-only mapping cached.
>
> [1] Unless the guest is allowed to modify the host's file; obviously
> truncation, holepunching, etc are going to evict pages from the host's
> page cache.
This is so correct. Guest does not not evict host page cache pages directly.
In case of virtio-pmem & DAX, guest clears guest page cache exceptional entries.
Its solely decision of host to take action on the host page cache pages.
In case of virtio-pmem, guest does not modify host file directly i.e don't
perform hole punch & truncation operation directly on host file.
Thanks,
Pankaj
next prev parent reply other threads:[~2019-01-14 7:15 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-01-09 14:47 [PATCH v3 0/5] kvm "virtio pmem" device Pankaj Gupta
2019-01-09 14:47 ` [PATCH v3 1/5] libnvdimm: nd_region flush callback support Pankaj Gupta
2019-01-09 14:47 ` [PATCH v3 2/5] virtio-pmem: Add virtio pmem driver Pankaj Gupta
2019-01-14 15:54 ` Michael S. Tsirkin
2019-01-14 15:54 ` Michael S. Tsirkin
[not found] ` <20190114105314-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2019-01-15 6:33 ` Pankaj Gupta
2019-01-15 6:33 ` Pankaj Gupta
2019-01-09 14:47 ` [PATCH v3 3/5] libnvdimm: add nd_region buffered dax_dev flag Pankaj Gupta
2019-01-09 14:47 ` [PATCH v3 4/5] ext4: disable map_sync for virtio pmem Pankaj Gupta
2019-01-09 14:47 ` [PATCH v3 5/5] xfs: " Pankaj Gupta
2019-01-09 14:47 ` Pankaj Gupta
2019-01-09 16:26 ` Darrick J. Wong
2019-01-09 18:08 ` Pankaj Gupta
[not found] ` <20190109144736.17452-1-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-10 1:26 ` [PATCH v3 0/5] kvm "virtio pmem" device Dave Chinner
2019-01-10 1:26 ` Dave Chinner
2019-01-10 2:40 ` Rik van Riel
2019-01-10 2:40 ` Rik van Riel
2019-01-10 10:17 ` Jan Kara
2019-01-10 10:17 ` Jan Kara
[not found] ` <20190110101757.GC15790-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org>
2019-01-13 1:38 ` Pankaj Gupta
2019-01-13 1:38 ` Pankaj Gupta
[not found] ` <1354249849.63357171.1547343519970.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-13 1:43 ` Dan Williams
2019-01-13 1:43 ` Dan Williams
[not found] ` <CAPcyv4hwcgTUpgNCefCGu4DvgkYBp5b=f+hJ+FC=s5APYKoycg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-01-13 2:17 ` [Qemu-devel] " Pankaj Gupta
2019-01-13 2:17 ` Pankaj Gupta
[not found] ` <540171952.63371441.1547345866585.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-14 9:55 ` Jan Kara
2019-01-14 9:55 ` Jan Kara
[not found] ` <20190114095520.GC13316-4I4JzKEfoa/jFM9bn6wA6Q@public.gmane.org>
2019-01-14 10:16 ` Pankaj Gupta
2019-01-14 10:16 ` Pankaj Gupta
2019-01-11 7:45 ` Pankaj Gupta
2019-01-11 7:45 ` Pankaj Gupta
[not found] ` <1326478078.61913951.1547192704870.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-13 23:29 ` Dave Chinner
2019-01-13 23:29 ` Dave Chinner
2019-01-13 23:38 ` Matthew Wilcox
2019-01-13 23:38 ` Matthew Wilcox
[not found] ` <20190113233820.GX6310-PfSpb0PWhxZc2C7mugBRk2EX/6BAtgUQ@public.gmane.org>
2019-01-14 2:50 ` Dave Chinner
2019-01-14 2:50 ` Dave Chinner
2019-01-14 7:15 ` Pankaj Gupta [this message]
2019-01-14 7:15 ` Pankaj Gupta
[not found] ` <942065073.64011540.1547450140670.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-14 21:25 ` Dave Chinner
2019-01-14 21:25 ` Dave Chinner
2019-01-14 21:35 ` Dan Williams
2019-01-14 21:35 ` Dan Williams
[not found] ` <CAPcyv4jtPcLV-s0sKNHwwk0ug7GLBV6699dpm1h3r2xSo879dg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2019-01-14 22:21 ` Dave Chinner
2019-01-14 22:21 ` Dave Chinner
2019-01-15 2:19 ` Michael S. Tsirkin
2019-01-15 2:19 ` Michael S. Tsirkin
[not found] ` <20190114205031-mutt-send-email-mst-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
2019-01-15 5:37 ` [Qemu-devel] " Pankaj Gupta
2019-01-15 5:37 ` Pankaj Gupta
2019-01-15 5:35 ` Pankaj Gupta
2019-01-15 5:35 ` Pankaj Gupta
[not found] ` <1684638419.64320214.1547530506805.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2019-01-15 20:42 ` Dave Chinner
2019-01-15 20:42 ` Dave Chinner
2019-02-04 22:56 ` security implications of caching with virtio pmem (was Re: [PATCH v3 0/5] kvm "virtio pmem" device) Michael S. Tsirkin
2019-02-05 7:29 ` [Qemu-devel] " Pankaj Gupta
2019-02-06 14:00 ` David Hildenbrand
2019-02-06 18:01 ` Michael S. Tsirkin
2019-02-11 7:29 ` [Qemu-devel] " Pankaj Gupta
2019-02-11 22:29 ` Dave Chinner
2019-02-11 22:58 ` David Hildenbrand
2019-02-11 23:07 ` Michael S. Tsirkin
-- strict thread matches above, loose matches on Subject: below --
2019-01-09 13:50 [PATCH v3 0/5] kvm "virtio pmem" device Pankaj Gupta
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