From: Jan Kara <jack@suse.cz>
To: Pankaj Gupta <pagupta@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
KVM list <kvm@vger.kernel.org>,
David Hildenbrand <david@redhat.com>,
linux-nvdimm <linux-nvdimm@ml01.01.org>,
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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>,
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xiaoguangrong eric <xiaoguangrong.eric@gmail.com>,
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Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: [Qemu-devel] [PATCH v3 0/5] kvm "virtio pmem" device
Date: Mon, 14 Jan 2019 10:55:20 +0100 [thread overview]
Message-ID: <20190114095520.GC13316@quack2.suse.cz> (raw)
In-Reply-To: <540171952.63371441.1547345866585.JavaMail.zimbra@redhat.com>
On Sat 12-01-19 21:17:46, Pankaj Gupta wrote:
> > > > 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.
OK, then I was just confused how virtio-pmem is going to work. Thanks for
explanation! So can I imagine this as guest mmaping the host file and
providing the mapped range as "NVDIMM pages" to the kernel inside the
guest? Or is it more complex?
Honza
--
Jan Kara <jack@suse.com>
SUSE Labs, CR
next prev parent reply other threads:[~2019-01-14 9:55 UTC|newest]
Thread overview: 39+ 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
2019-01-15 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 16:26 ` Darrick J. Wong
2019-01-09 18:08 ` Pankaj Gupta
2019-01-10 1:26 ` [PATCH v3 0/5] kvm "virtio pmem" device Dave Chinner
2019-01-10 2:40 ` Rik van Riel
2019-01-10 10:17 ` Jan Kara
2019-01-13 1:38 ` Pankaj Gupta
2019-01-13 1:43 ` Dan Williams
2019-01-13 2:17 ` [Qemu-devel] " Pankaj Gupta
2019-01-14 9:55 ` Jan Kara [this message]
2019-01-14 10:16 ` Pankaj Gupta
2019-01-11 7:45 ` Pankaj Gupta
2019-01-13 23:29 ` Dave Chinner
2019-01-13 23:38 ` Matthew Wilcox
2019-01-14 2:50 ` Dave Chinner
2019-01-14 7:15 ` Pankaj Gupta
2019-01-14 21:25 ` Dave Chinner
2019-01-14 21:35 ` Dan Williams
2019-01-14 22:21 ` Dave Chinner
2019-01-15 2:19 ` Michael S. Tsirkin
2019-01-15 5:37 ` [Qemu-devel] " Pankaj Gupta
2019-01-15 5:35 ` Pankaj Gupta
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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