From: Pankaj Gupta <pagupta@redhat.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>, KVM list <kvm@vger.kernel.org>,
David Hildenbrand <david@redhat.com>,
linux-nvdimm <linux-nvdimm@ml01.01.org>,
Jason Wang <jasowang@redhat.com>,
Dave Chinner <david@fromorbit.com>,
Qemu Developers <qemu-devel@nongnu.org>,
virtualization@lists.linux-foundation.org,
adilger kernel <adilger.kernel@dilger.ca>,
Ross Zwisler <zwisler@kernel.org>,
dave jiang <dave.jiang@intel.com>,
darrick wong <darrick.wong@oracle.com>,
vishal l verma <vishal.l.verma@intel.com>,
"Michael S. Tsirkin" <mst@redhat.com>,
Matthew Wilcox <willy@infradead.org>,
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Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device
Date: Sat, 12 Jan 2019 21:17:46 -0500 (EST) [thread overview]
Message-ID: <540171952.63371441.1547345866585.JavaMail.zimbra@redhat.com> (raw)
Message-ID: <20190113021746.zIGLfqHkB8vIxECi_fXItVzXRHXU9FZb7pZDqzVIJls@z> (raw)
In-Reply-To: <CAPcyv4hwcgTUpgNCefCGu4DvgkYBp5b=f+hJ+FC=s5APYKoycg@mail.gmail.com>
> >
> >
> >
> > >
> > > On Thu 10-01-19 12:26:17, Dave Chinner wrote:
> > > > On Wed, Jan 09, 2019 at 08:17:31PM +0530, Pankaj Gupta wrote:
> > > > > This patch series has implementation for "virtio pmem".
> > > > > "virtio pmem" is fake persistent memory(nvdimm) in guest
> > > > > which allows to bypass the guest page cache. This also
> > > > > implements a VIRTIO based asynchronous flush mechanism.
> > > >
> > > > Hmmmm. Sharing the host page cache direct into the guest VM. Sounds
> > > > like a good idea, but.....
> > > >
> > > > This means the guest VM can now run timing attacks to observe host
> > > > side page cache residency, and depending on the implementation I'm
> > > > guessing that the guest will be able to control host side page
> > > > cache eviction, too (e.g. via discard or hole punch operations).
> > > >
> > > > Which means this functionality looks to me like a new vector for
> > > > information leakage into and out of the guest VM via guest
> > > > controlled host page cache manipulation.
> > > >
> > > > https://arxiv.org/pdf/1901.01161
> > > >
> > > > I might be wrong, but if I'm not we're going to have to be very
> > > > careful about how guest VMs can access and manipulate host side
> > > > resources like the page cache.....
> > >
> > > Right. Thinking about this I would be more concerned about the fact that
> > > guest can effectively pin amount of host's page cache upto size of the
> > > device/file passed to guest as PMEM, can't it Pankaj? Or is there some
> > > QEMU
> > > magic that avoids this?
> >
> > Yes, guest will pin these host page cache pages using 'get_user_pages' by
> > elevating the page reference count. But these pages can be reclaimed by
> > host
> > at any time when there is memory pressure.
>
> Wait, how can the guest pin the host pages? I would expect this to
> happen only when using vfio and device assignment. Otherwise, no the
> host can't reclaim a pinned page, that's the whole point of a pin to
> prevent the mm from reclaiming ownership.
yes. You are right I just used the pin word but it does not actually pin pages
permanently. I had gone through the discussion on existing problems with
get_user_pages and DMA e.g [1] to understand Jan's POV. It does mention GUP
pin pages so I also used the word 'pin'. But guest does not permanently pin
these pages and these pages can be reclaimed by host.
>
> > KVM does not permanently pin pages. vfio does that but we are not using
> > it here.
>
> Right, so I'm confused by your pin assertion above.
Sorry! for the confusion.
[1] https://lwn.net/Articles/753027/
Thanks,
Pankaj
next prev parent reply other threads:[~2019-01-13 2:17 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 ` Pankaj Gupta [this message]
2019-01-13 2:17 ` [Qemu-devel] " 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
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
2019-01-09 14:46 ` [Qemu-devel] " Pankaj Gupta
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