From: Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
To: Dan Williams <dan.j.williams-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Cc: Kevin Wolf <kwolf-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>,
xiaoguangrong eric
<xiaoguangrong.eric-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
KVM list <kvm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Pankaj Gupta <pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Stefan Hajnoczi
<stefanha-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>,
David Hildenbrand <david-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
ross zwisler
<ross.zwisler-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
Qemu Developers
<qemu-devel-qX2TKyscuCcdnm+yROfE0A@public.gmane.org>,
Christoph Hellwig <hch-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>,
Linux MM <linux-mm-Bw31MaZKKs3YtjvyW6yDsg@public.gmane.org>,
Stefan Hajnoczi
<stefanha-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
linux-nvdimm
<linux-nvdimm-y27Ovi1pjclAfugRpC6u6w@public.gmane.org>,
Paolo Bonzini <pbonzini-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
Nitesh Narayan Lal
<nilal-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
Subject: Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver
Date: Fri, 20 Oct 2017 01:00:49 -0700 [thread overview]
Message-ID: <20171020080049.GA25471@infradead.org> (raw)
In-Reply-To: <CAPcyv4j=Cdp68C15HddKaErpve2UGRfSTiL6bHiS=3gQybz9pg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
On Thu, Oct 19, 2017 at 11:21:26AM -0700, Dan Williams wrote:
> The difference is that nvdimm_flush() is not mandatory, and that the
> platform will automatically perform the same flush at power-fail.
> Applications should be able to assume that if they are using MAP_SYNC
> that no other coordination with the kernel or the hypervisor is
> necessary.
>
> Advertising this as a generic Persistent Memory range to the guest
> means that the guest could theoretically use it with device-dax where
> there is no driver or filesystem sync interface. The hypervisor will
> be waiting for flush notifications and the guest will just issue cache
> flushes and sfence instructions. So, as far as I can see we need to
> differentiate this virtio-model from standard "Persistent Memory" to
> the guest and remove the possibility of guests/applications making the
> wrong assumption.
So add a flag that it is not. We already have the nd_volatile type,
that is special. For now only in Linux, but I think adding this type
to the spec eventually would be very useful for efficiently exposing
directly mappable device to VM guests.
next prev parent reply other threads:[~2017-10-20 8:00 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-10-12 15:50 [RFC 0/2] KVM "fake DAX" device flushing Pankaj Gupta
2017-10-12 15:50 ` [RFC 1/2] pmem: Move reusable code to base header files Pankaj Gupta
2017-10-12 20:42 ` Dan Williams
2017-10-12 21:27 ` [Qemu-devel] " Pankaj Gupta
[not found] ` <20171012155027.3277-1-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-12 15:50 ` [RFC 2/2] KVM: add virtio-pmem driver Pankaj Gupta
2017-10-12 20:51 ` Dan Williams
2017-10-12 21:25 ` Pankaj Gupta
2017-10-12 21:54 ` Dan Williams
[not found] ` <CAPcyv4gkri7t+3Unf0sc9AHMnz-v9G_qV_bJppLjUUNAn7drrQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-12 22:18 ` Pankaj Gupta
2017-10-12 22:27 ` Rik van Riel
2017-10-12 22:39 ` Pankaj Gupta
2017-10-12 22:52 ` Pankaj Gupta
2017-10-12 22:59 ` Dan Williams
2017-10-12 23:07 ` Pankaj Gupta
2017-10-13 9:44 ` Stefan Hajnoczi
2017-10-13 10:48 ` Pankaj Gupta
[not found] ` <24301306.20068579.1507891695416.JavaMail.zimbra-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-16 14:47 ` Stefan Hajnoczi
2017-10-16 15:58 ` Dan Williams
2017-10-16 17:04 ` Pankaj Gupta
[not found] ` <20171013094431.GA27308-lxVrvc10SDRcolVlb+j0YCZi+YwRKgec@public.gmane.org>
2017-10-13 15:25 ` Dan Williams
[not found] ` <20171012155027.3277-3-pagupta-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2017-10-17 7:16 ` Christoph Hellwig
2017-10-17 7:40 ` [Qemu-devel] " Pankaj Gupta
2017-10-17 8:02 ` Christoph Hellwig
2017-10-17 8:30 ` Pankaj Gupta
2017-10-18 13:03 ` Stefan Hajnoczi
2017-10-18 15:51 ` Dan Williams
[not found] ` <CAPcyv4h6aFkyHhh4R4DTznbSCLf9CuBoszk0Q1gB5EKNcp_SeQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-19 8:01 ` Stefan Hajnoczi
2017-10-19 8:01 ` Christoph Hellwig
[not found] ` <20171019080149.GB10089-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-10-19 18:21 ` Dan Williams
[not found] ` <CAPcyv4j=Cdp68C15HddKaErpve2UGRfSTiL6bHiS=3gQybz9pg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2017-10-20 8:00 ` Christoph Hellwig [this message]
[not found] ` <20171020080049.GA25471-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
2017-10-20 15:05 ` Dan Williams
2017-10-20 16:06 ` Christoph Hellwig
2017-10-20 16:11 ` Dan Williams
2017-10-12 15:50 ` [RFC] QEMU: Add virtio pmem device Pankaj Gupta
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