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From: Haozhong Zhang <haozhong.zhang@intel.com>
To: Jan Beulich <JBeulich@suse.com>
Cc: Juergen Gross <JGross@suse.com>,
	Kevin Tian <kevin.tian@intel.com>, Wei Liu <wei.liu2@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>,
	George Dunlap <george.dunlap@citrix.com>,
	"xen-devel@lists.xen.org" <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: Tue, 29 Mar 2016 18:10:36 +0800	[thread overview]
Message-ID: <20160329101036.GC3650@hz-desktop.sh.intel.com> (raw)
In-Reply-To: <56FA62F302000078000E0C25@prv-mh.provo.novell.com>

On 03/29/16 03:11, Jan Beulich wrote:
> >>> On 29.03.16 at 10:47, <haozhong.zhang@intel.com> wrote:
> > On 03/17/16 22:21, Haozhong Zhang wrote:
> >> On 03/17/16 14:00, Ian Jackson wrote:
> >> > Haozhong Zhang writes ("Re: [Xen-devel] [RFC Design Doc] Add vNVDIMM support for Xen"):
> >> > > QEMU keeps mappings of guest memory because (1) that mapping is
> >> > > created by itself, and/or (2) certain device emulation needs to access
> >> > > the guest memory. But for vNVDIMM, I'm going to move the creation of
> >> > > its mappings out of qemu to toolstack and vNVDIMM in QEMU does not
> >> > > access vNVDIMM pages mapped to guest, so it's not necessary to let
> >> > > qemu keeps vNVDIMM mappings.
> >> > 
> >> > I'm confused by this.
> >> > 
> >> > Suppose a guest uses an emulated device (or backend) provided by qemu,
> >> > to do DMA to an vNVDIMM.  Then qemu will need to map the real NVDIMM
> >> > pages into its own address space, so that it can write to the memory
> >> > (ie, do the virtual DMA).
> >> > 
> >> > That virtual DMA might well involve a direct mapping in the kernel
> >> > underlying qemu: ie, qemu might use O_DIRECT to have its kernel write
> >> > directly to the NVDIMM, and with luck the actual device backing the
> >> > virtual device will be able to DMA to the NVDIMM.
> >> > 
> >> > All of this seems to me to mean that qemu needs to be able to map
> >> > its guest's parts of NVDIMMs
> >> > 
> >> > There are probably other example: memory inspection systems used by
> >> > virus scanners etc.; debuggers used to inspect a guest from outside;
> >> > etc.
> >> > 
> >> > I haven't even got started on save/restore...
> >> > 
> >> 
> >> Oops, so many cases I missed. Thanks Ian for pointing out all these!
> >> Now I need to reconsider how to manage guest permissions for NVDIMM pages.
> >> 
> > 
> > I still cannot find a neat approach to manage guest permissions for
> > nvdimm pages. A possible one is to use a per-domain bitmap to track
> > permissions: each bit corresponding to an nvdimm page. The bitmap can
> > save lots of spaces and even be stored in the normal ram, but
> > operating it for a large nvdimm range, especially for a contiguous
> > one, is slower than rangeset.
> 
> I don't follow: What would a single bit in that bitmap mean? Any
> guest may access the page? That surely wouldn't be what we
> need.
>

For a host having a N pages of nvdimm, each domain will have a N bits
bitmap. If the m'th bit of a domain's bitmap is set, then that domain
has the permission to access the m'th host nvdimm page.

> > BTW, if I take the other way to map nvdimm pages to guest
> > (http://lists.xenproject.org/archives/html/xen-devel/2016-03/msg01972.html)
> > | 2. Or, given the same inputs, we may combine above two steps into a new
> > |    dom0 system call that (1) gets the SPA ranges, (2) calls xen
> > |    hypercall to map SPA ranges
> > and treat nvdimm as normal ram, then xen will not need to use rangeset
> > or above bitmap to track guest permissions for nvdimm? But looking at
> > how qemu currently populates guest memory via XENMEM_populate_physmap
> > , and other hypercalls like XENMEM_[in|de]crease_reservation, it looks
> > like that mapping a _dedicated_ piece of host ram to guest is not
> > allowed out of the hypervisor (and not allowed even in dom0 kernel)?
> > Is it for security concerns, e.g. avoiding a malfunctioned dom0 leaking
> > guest memory?
> 
> Well, it's simply because RAM is a resource managed through
> allocation/freeing, instead of via reserving chunks for special
> purposes.
> 

So that means xen can always ensure the ram assigned to a guest is
what the guest is permitted to access, so no data structures like
iomem_caps is needed for ram. If I have to introduce a hypercall that
maps the dedicated host ram/nvdimm to guest, then the explicit
permission management is still needed, regardless of who (dom0 kernel,
qemu or toolstack) will use it. Right?

Haozhong

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  reply	other threads:[~2016-03-29 10:10 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 [this message]
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
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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