From: "Jan Beulich" <JBeulich@suse.com>
To: Haozhong Zhang <haozhong.zhang@intel.com>
Cc: Juergen Gross <JGross@suse.com>,
Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@citrix.com>,
Ian Campbell <ian.campbell@citrix.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>,
George Dunlap <George.Dunlap@eu.citrix.com>,
Andrew Cooper <andrew.cooper3@citrix.com>,
Ian Jackson <ian.jackson@eu.citrix.com>,
xen-devel@lists.xen.org, Jun Nakajima <jun.nakajima@intel.com>,
Xiao Guangrong <guangrong.xiao@linux.intel.com>,
Keir Fraser <keir@xen.org>
Subject: Re: [RFC Design Doc] Add vNVDIMM support for Xen
Date: Thu, 18 Feb 2016 10:17:21 -0700 [thread overview]
Message-ID: <56C60AB102000078000D3D22@prv-mh.provo.novell.com> (raw)
In-Reply-To: <20160201054414.GA25211@hz-desktop.sh.intel.com>
>>> On 01.02.16 at 06:44, <haozhong.zhang@intel.com> wrote:
> This design treats host NVDIMM devices as ordinary MMIO devices:
Wrt the cachability note earlier on, I assume you're aware that with
the XSA-154 changes we disallow any cachable mappings of MMIO
by default.
> (1) Dom0 Linux NVDIMM driver is responsible to detect (through NFIT)
> and drive host NVDIMM devices (implementing block device
> interface). Namespaces and file systems on host NVDIMM devices
> are handled by Dom0 Linux as well.
>
> (2) QEMU mmap(2) the pmem NVDIMM devices (/dev/pmem0) into its
> virtual address space (buf).
>
> (3) QEMU gets the host physical address of buf, i.e. the host system
> physical address that is occupied by /dev/pmem0, and calls Xen
> hypercall XEN_DOMCTL_memory_mapping to map it to a DomU.
>
> (ACPI part is described in Section 3.3 later)
>
> Above (1)(2) have already been done in current QEMU. Only (3) is
> needed to implement in QEMU. No change is needed in Xen for address
> mapping in this design.
>
> Open: It seems no system call/ioctl is provided by Linux kernel to
> get the physical address from a virtual address.
> /proc/<qemu_pid>/pagemap provides information of mapping from
> VA to PA. Is it an acceptable solution to let QEMU parse this
> file to get the physical address?
>
> Open: For a large pmem, mmap(2) is very possible to not map all SPA
> occupied by pmem at the beginning, i.e. QEMU may not be able to
> get all SPA of pmem from buf (in virtual address space) when
> calling XEN_DOMCTL_memory_mapping.
> Can mmap flag MAP_LOCKED or mlock(2) be used to enforce the
> entire pmem being mmaped?
A fundamental question I have here is: Why does qemu need to
map this at all? It shouldn't itself need to access those ranges,
since the guest is given direct access. It would seem quite a bit
more natural if qemu simply inquired to underlying GFN range(s)
and handed those to Xen for translation to MFNs and mapping
into guest space.
> I notice that current XEN_DOMCTL_memory_mapping does not make santiy
> check for the physical address and size passed from caller
> (QEMU). Can QEMU be always trusted? If not, we would need to make Xen
> aware of the SPA range of pmem so that it can refuse map physical
> address in neither the normal ram nor pmem.
I'm not sure what missing sanity checks this is about: The handling
involves two iomem_access_permitted() calls.
> 3.3 Guest ACPI Emulation
>
> 3.3.1 My Design
>
> Guest ACPI emulation is composed of two parts: building guest NFIT
> and SSDT that defines ACPI namespace devices for NVDIMM, and
> emulating guest _DSM.
>
> (1) Building Guest ACPI Tables
>
> This design reuses and extends hvmloader's existing mechanism that
> loads passthrough ACPI tables from binary files to load NFIT and
> SSDT tables built by QEMU:
> 1) Because the current QEMU does not building any ACPI tables when
> it runs as the Xen device model, this design needs to patch QEMU
> to build NFIT and SSDT (so far only NFIT and SSDT) in this case.
>
> 2) QEMU copies NFIT and SSDT to the end of guest memory below
> 4G. The guest address and size of those tables are written into
> xenstore (/local/domain/domid/hvmloader/dm-acpi/{address,length}).
>
> 3) hvmloader is patched to probe and load device model passthrough
> ACPI tables from above xenstore keys. The detected ACPI tables
> are then appended to the end of existing guest ACPI tables just
> like what current construct_passthrough_tables() does.
>
> Reasons for this design are listed below:
> - NFIT and SSDT in question are quite self-contained, i.e. they do
> not refer to other ACPI tables and not conflict with existing
> guest ACPI tables in Xen. Therefore, it is safe to copy them from
> QEMU and append to existing guest ACPI tables.
How is this not conflicting being guaranteed? In particular I don't
see how tables containing AML code and coming from different
sources won't possibly cause ACPI name space collisions.
> 3.3.3 Alternative Design 2: keeping in Xen
>
> Alternative to switching to QEMU, another design would be building
> NFIT and SSDT in hvmloader or toolstack.
>
> The amount and parameters of sub-structures in guest NFIT vary
> according to different vNVDIMM configurations that can not be decided
> at compile-time. In contrast, current hvmloader and toolstack can
> only build static ACPI tables, i.e. their contents are decided
> statically at compile-time and independent from the guest
> configuration. In order to build guest NFIT at runtime, this design
> may take following steps:
> (1) xl converts NVDIMM configurations in xl.cfg to corresponding QEMU
> options,
>
> (2) QEMU accepts above options, figures out the start SPA range
> address/size/NVDIMM device handles/..., and writes them in
> xenstore. No ACPI table is built by QEMU.
>
> (3) Either xl or hvmloader reads above parameters from xenstore and
> builds the NFIT table.
>
> For guest SSDT, it would take more work. The ACPI namespace devices
> are defined in SSDT by AML, so an AML builder would be needed to
> generate those definitions at runtime.
I'm not sure this last half sentence is true: We do some dynamic
initialization of the pre-generated DSDT already, using the runtime
populated block at ACPI_INFO_PHYSICAL_ADDRESS.
Jan
next prev parent reply other threads:[~2016-02-18 17:17 UTC|newest]
Thread overview: 121+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-01 5:44 [RFC Design Doc] Add vNVDIMM support for Xen Haozhong Zhang
2016-02-01 18:25 ` Andrew Cooper
2016-02-02 3:27 ` Tian, Kevin
2016-02-02 3:44 ` Haozhong Zhang
2016-02-02 11:09 ` Andrew Cooper
2016-02-02 6:33 ` Tian, Kevin
2016-02-02 7:39 ` Zhang, Haozhong
2016-02-02 7:48 ` Tian, Kevin
2016-02-02 7:53 ` Zhang, Haozhong
2016-02-02 8:03 ` Tian, Kevin
2016-02-02 8:49 ` Zhang, Haozhong
2016-02-02 19:01 ` Konrad Rzeszutek Wilk
2016-02-02 17:11 ` Stefano Stabellini
2016-02-03 7:00 ` Haozhong Zhang
2016-02-03 9:13 ` Jan Beulich
2016-02-03 14:09 ` Andrew Cooper
2016-02-03 14:23 ` Haozhong Zhang
2016-02-05 14:40 ` Ross Philipson
2016-02-06 1:43 ` Haozhong Zhang
2016-02-06 16:17 ` Ross Philipson
2016-02-03 12:02 ` Stefano Stabellini
2016-02-03 13:11 ` Haozhong Zhang
2016-02-03 14:20 ` Andrew Cooper
2016-02-04 3:10 ` Haozhong Zhang
2016-02-03 15:16 ` George Dunlap
2016-02-03 15:22 ` Stefano Stabellini
2016-02-03 15:35 ` Konrad Rzeszutek Wilk
2016-02-03 15:35 ` George Dunlap
2016-02-04 2:55 ` Haozhong Zhang
2016-02-04 12:24 ` Stefano Stabellini
2016-02-15 3:16 ` Zhang, Haozhong
2016-02-16 11:14 ` Stefano Stabellini
2016-02-16 12:55 ` Jan Beulich
2016-02-17 9:03 ` Haozhong Zhang
2016-03-04 7:30 ` Haozhong Zhang
2016-03-16 12:55 ` Haozhong Zhang
2016-03-16 13:13 ` Konrad Rzeszutek Wilk
2016-03-16 13:16 ` Jan Beulich
2016-03-16 13:55 ` Haozhong Zhang
2016-03-16 14:23 ` Jan Beulich
2016-03-16 14:55 ` Haozhong Zhang
2016-03-16 15:23 ` Jan Beulich
2016-03-17 8:58 ` Haozhong Zhang
2016-03-17 11:04 ` Jan Beulich
2016-03-17 12:44 ` Haozhong Zhang
2016-03-17 12:59 ` Jan Beulich
2016-03-17 13:29 ` Haozhong Zhang
2016-03-17 13:52 ` Jan Beulich
2016-03-17 14:00 ` Ian Jackson
2016-03-17 14:21 ` Haozhong Zhang
2016-03-29 8:47 ` Haozhong Zhang
2016-03-29 9:11 ` Jan Beulich
2016-03-29 10:10 ` Haozhong Zhang
2016-03-29 10:49 ` Jan Beulich
2016-04-08 5:02 ` Haozhong Zhang
2016-04-08 15:52 ` Jan Beulich
2016-04-12 8:45 ` Haozhong Zhang
2016-04-21 5:09 ` Haozhong Zhang
2016-04-21 7:04 ` Jan Beulich
2016-04-22 2:36 ` Haozhong Zhang
2016-04-22 8:24 ` Jan Beulich
2016-04-22 10:16 ` Haozhong Zhang
2016-04-22 10:53 ` Jan Beulich
2016-04-22 12:26 ` Haozhong Zhang
2016-04-22 12:36 ` Jan Beulich
2016-04-22 12:54 ` Haozhong Zhang
2016-04-22 13:22 ` Jan Beulich
2016-03-17 13:32 ` Konrad Rzeszutek Wilk
2016-02-03 15:47 ` Konrad Rzeszutek Wilk
2016-02-04 2:36 ` Haozhong Zhang
2016-02-15 9:04 ` Zhang, Haozhong
2016-02-02 19:15 ` Konrad Rzeszutek Wilk
2016-02-03 8:28 ` Haozhong Zhang
2016-02-03 9:18 ` Jan Beulich
2016-02-03 12:22 ` Haozhong Zhang
2016-02-03 12:38 ` Jan Beulich
2016-02-03 12:49 ` Haozhong Zhang
2016-02-03 14:30 ` Andrew Cooper
2016-02-03 14:39 ` Jan Beulich
2016-02-15 8:43 ` Haozhong Zhang
2016-02-15 11:07 ` Jan Beulich
2016-02-17 9:01 ` Haozhong Zhang
2016-02-17 9:08 ` Jan Beulich
2016-02-18 7:42 ` Haozhong Zhang
2016-02-19 2:14 ` Konrad Rzeszutek Wilk
2016-03-01 7:39 ` Haozhong Zhang
2016-03-01 18:33 ` Ian Jackson
2016-03-01 18:49 ` Konrad Rzeszutek Wilk
2016-03-02 7:14 ` Haozhong Zhang
2016-03-02 13:03 ` Jan Beulich
2016-03-04 2:20 ` Haozhong Zhang
2016-03-08 9:15 ` Haozhong Zhang
2016-03-08 9:27 ` Jan Beulich
2016-03-09 12:22 ` Haozhong Zhang
2016-03-09 16:17 ` Jan Beulich
2016-03-10 3:27 ` Haozhong Zhang
2016-03-17 11:05 ` Ian Jackson
2016-03-17 13:37 ` Haozhong Zhang
2016-03-17 13:56 ` Jan Beulich
2016-03-17 14:22 ` Haozhong Zhang
2016-03-17 14:12 ` Xu, Quan
2016-03-17 14:22 ` Zhang, Haozhong
2016-03-07 20:53 ` Konrad Rzeszutek Wilk
2016-03-08 5:50 ` Haozhong Zhang
2016-02-18 17:17 ` Jan Beulich [this message]
2016-02-24 13:28 ` Haozhong Zhang
2016-02-24 14:00 ` Ross Philipson
2016-02-24 16:42 ` Haozhong Zhang
2016-02-24 17:50 ` Ross Philipson
2016-02-24 14:24 ` Jan Beulich
2016-02-24 15:48 ` Haozhong Zhang
2016-02-24 16:54 ` Jan Beulich
2016-02-28 14:48 ` Haozhong Zhang
2016-02-29 9:01 ` Jan Beulich
2016-02-29 9:45 ` Haozhong Zhang
2016-02-29 10:12 ` Jan Beulich
2016-02-29 11:52 ` Haozhong Zhang
2016-02-29 12:04 ` Jan Beulich
2016-02-29 12:22 ` Haozhong Zhang
2016-03-01 13:51 ` Ian Jackson
2016-03-01 15:04 ` Jan Beulich
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