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From: Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>,
	KVM list <kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"Michael S. Tsirkin"
	<mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	linux-nvdimm
	<linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org>,
	Jason Wang <jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Dave Chinner <david-FqsqvQoI3Ljby3iVrkZq2A@public.gmane.org>,
	Qemu Developers
	<qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>,
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	darrick wong
	<darrick.wong-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>,
	David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Matthew Wilcox <willy-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
	Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
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	Rik van Riel <riel-ebMLmSuQjDVBDgjK7y7TUQ@public.gmane.org>,
	Stefan Hajnoczi
	<stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	lcapitulino-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org,
	Kevin Wolf <kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Nitesh Narayan Lal
	<nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	Theodore Ts'o <tytso-3s7WtUTddSA@public.gmane.org>,
	xiaoguangrong eric <xiaoguangrong.eric@gmai
Subject: Re: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device
Date: Sat, 12 Jan 2019 21:17:46 -0500 (EST)
Message-ID: <540171952.63371441.1547345866585.JavaMail.zimbra@redhat.com> (raw)
In-Reply-To: <CAPcyv4hwcgTUpgNCefCGu4DvgkYBp5b=f+hJ+FC=s5APYKoycg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>


> >
> >
> >
> > >
> > > 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

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>,
	Christoph Hellwig <hch@infradead.org>,
	Linux ACPI <linux-acpi@vger.kernel.org>,
	jmoyer <jmoyer@redhat.com>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	Rik van Riel <riel@surriel.com>,
	Stefan Hajnoczi <stefanha@redhat.com>,
	Igor Mammedov <imammedo@redhat.com>,
	lcapitulino@redhat.com, Kevin Wolf <kwolf@redhat.com>,
	Nitesh Narayan Lal <nilal@redhat.com>,
	Theodore Ts'o <tytso@mit.edu>,
	xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
	"Rafael J. Wysocki" <rjw@rjwysocki.net>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	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)
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

  parent reply index

Thread overview: 62+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-01-09 14:47 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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