linux-kernel - Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20171020080049.GA25471@infradead.org>
Date:   Fri, 20 Oct 2017 01:00:49 -0700
From:   Christoph Hellwig <hch@...radead.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Stefan Hajnoczi <stefanha@...il.com>,
        Pankaj Gupta <pagupta@...hat.com>,
        Kevin Wolf <kwolf@...hat.com>,
        haozhong zhang <haozhong.zhang@...el.com>,
        Jan Kara <jack@...e.cz>,
        xiaoguangrong eric <xiaoguangrong.eric@...il.com>,
        KVM list <kvm@...r.kernel.org>,
        David Hildenbrand <david@...hat.com>,
        linux-nvdimm <linux-nvdimm@...1.01.org>,
        ross zwisler <ross.zwisler@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Qemu Developers <qemu-devel@...gnu.org>,
        Linux MM <linux-mm@...ck.org>,
        Stefan Hajnoczi <stefanha@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Nitesh Narayan Lal <nilal@...hat.com>
Subject: Re: [Qemu-devel] [RFC 2/2] KVM: add virtio-pmem driver

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.