Re: [RFC XEN PATCH v2 00/15] Add vNVDIMM support to HVM domains

From: Dan Williams <dan.j.williams@intel.com>
To: Haozhong Zhang <haozhong.zhang@intel.com>
Cc: Wei Liu <wei.liu2@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Ian Jackson <ian.jackson@eu.citrix.com>,
	xen-devel@lists.xen.org, Jan Beulich <jbeulich@suse.com>,
	Konrad Rzeszutek Wilk <konrad@darnok.org>,
	Daniel De Graaf <dgdegra@tycho.nsa.gov>
Subject: Re: [RFC XEN PATCH v2 00/15] Add vNVDIMM support to HVM domains
Date: Wed, 29 Mar 2017 21:20:26 -0700	[thread overview]
Message-ID: <CAPcyv4gSX+j1s4C7YUd-p1hCr=dJkAYOOo9aQd_jVQy4uJqEUg@mail.gmail.com> (raw)
In-Reply-To: <20170320000949.24675-1-haozhong.zhang@intel.com>

On Sun, Mar 19, 2017 at 5:09 PM, Haozhong Zhang
<haozhong.zhang@intel.com> wrote:
> This is v2 RFC patch series to add vNVDIMM support to HVM domains.
> v1 can be found at https://lists.xenproject.org/archives/html/xen-devel/2016-10/msg00424.html.
>
> No label and no _DSM except function 0 "query implemented functions"
> is supported by this version, but they will be added by future patches.
>
> The corresponding Qemu patch series is sent in another thread
> "[RFC QEMU PATCH v2 00/10] Implement vNVDIMM for Xen HVM guest".
>
> All patch series can be found at
>   Xen:  https://github.com/hzzhan9/xen.git nvdimm-rfc-v2
>   Qemu: https://github.com/hzzhan9/qemu.git xen-nvdimm-rfc-v2
>
> Changes in v2
> ==============
>
> - One of the primary changes in v2 is dropping the linux kernel
>   patches, which were used to reserve on host pmem for placing its
>   frametable and M2P table. In v2, we add a management tool xen-ndctl
>   which is used in Dom0 to notify Xen hypervisor of which storage can
>   be used to manage the host pmem.
>
>   For example,
>   1.   xen-ndctl setup 0x240000 0x380000 0x380000 0x3c0000
>     tells Xen hypervisor to use host pmem pages at MFN 0x380000 ~
>     0x3c0000 to manage host pmem pages at MFN 0x240000 ~ 0x380000.
>     I.e. the former is used to place the frame table and M2P table of
>     both ranges of pmem pages.
>
>   2.   xen-ndctl setup 0x240000 0x380000
>     tells Xen hypervisor to use the regular RAM to manage the host
>     pmem pages at MFN 0x240000 ~ 0x380000. I.e the regular RMA is used
>     to place the frame table and M2P table.
>
> - Another primary change in v2 is dropping the support to map files on
>   the host pmem to HVM domains as virtual NVDIMMs, as I cannot find a
>   stable to fix the fiemap of host files. Instead, we can rely on the
>   ability added in Linux kernel v4.9 that enables creating multiple
>   pmem namespaces on a single nvdimm interleave set.

This restriction is unfortunate, and it seems to limit the future
architecture of the pmem driver. We may not always be able to
guarantee a contiguous physical address range to Xen for a given
namespace and may want to concatenate disjoint physical address ranges
into a logically contiguous namespace.

Is there a resource I can read more about why the hypervisor needs to
have this M2P mapping for nvdimm support?

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