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>,
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>,
IanJackson <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: Thu, 17 Mar 2016 16:58:33 +0800 [thread overview]
Message-ID: <20160317085833.GC4005@hz-desktop.sh.intel.com> (raw)
In-Reply-To: <56E9888802000078000DD3F9@prv-mh.provo.novell.com>
On 03/16/16 09:23, Jan Beulich wrote:
> >>> On 16.03.16 at 15:55, <haozhong.zhang@intel.com> wrote:
> > On 03/16/16 08:23, Jan Beulich wrote:
> >> >>> On 16.03.16 at 14:55, <haozhong.zhang@intel.com> wrote:
> >> > On 03/16/16 07:16, Jan Beulich wrote:
> >> >> Which reminds me: When considering a file on NVDIMM, how
> >> >> are you making sure the mapping of the file to disk (i.e.
> >> >> memory) blocks doesn't change while the guest has access
> >> >> to it, e.g. due to some defragmentation going on?
> >> >
> >> > The current linux kernel 4.5 has an experimental "raw device dax
> >> > support" (enabled by removing "depends on BROKEN" from "config
> >> > BLK_DEV_DAX") which can guarantee the consistent mapping. The driver
> >> > developers are going to make it non-broken in linux kernel 4.6.
> >>
> >> But there you talk about full devices, whereas my question was
> >> for files.
> >>
> >
> > the raw device dax support is for files on NVDIMM.
>
> Okay, I can only trust you here. I thought FS_DAX is the file level
> thing.
>
> >> >> And
> >> >> talking of fragmentation - how do you mean to track guest
> >> >> permissions for an unbounded number of address ranges?
> >> >>
> >> >
> >> > In this case range structs in iomem_caps for NVDIMMs may consume a lot
> >> > of memory, so I think they are another candidate that should be put in
> >> > the reserved area on NVDIMM. If we only allow to grant access
> >> > permissions to NVDIMM page by page (rather than byte), the number of
> >> > range structs for each NVDIMM in the worst case is still decidable.
> >>
> >> Of course the permission granularity is going to by pages, not
> >> bytes (or else we couldn't allow the pages to be mapped into
> >> guest address space). And the limit on the per-domain range
> >> sets isn't going to be allowed to be bumped significantly, at
> >> least not for any of the existing ones (or else you'd have to
> >> prove such bumping can't be abused).
> >
> > What is that limit? the total number of range structs in per-domain
> > range sets? I must miss something when looking through 'case
> > XEN_DOMCTL_iomem_permission' of do_domctl() and didn't find that
> > limit, unless it means alloc_range() will fail when there are lots of
> > range structs.
>
> Oh, I'm sorry, that was a different set of range sets I was
> thinking about. But note that excessive creation of ranges
> through XEN_DOMCTL_iomem_permission is not a security issue
> just because of XSA-77, i.e. we'd still not knowingly allow a
> severe increase here.
>
I didn't notice that multiple domains can all have access permission
to an iomem range, i.e. there can be multiple range structs for a
single iomem range. If range structs for NVDIMM are put on NVDIMM,
then there would be still a huge amount of them on NVDIMM in the worst
case (maximum number of domains * number of NVDIMM pages).
A workaround is to only allow a range of NVDIMM pages be accessed by a
single domain. Whenever we add the access permission of NVDIMM pages
to a domain, we also remove the permission from its current
grantee. In this way, we only need to put 'number of NVDIMM pages'
range structs on NVDIMM in the worst case.
> >> Putting such control
> >> structures on NVDIMM is a nice idea, but following our isolation
> >> model for normal memory, any such memory used by Xen
> >> would then need to be (made) inaccessible to Dom0.
> >
> > I'm not clear how this is done. By marking those inaccessible pages as
> > unpresent in dom0's page table? Or any example I can follow?
>
> That's the problem - so far we had no need to do so since Dom0
> was only ever allowed access to memory Xen didn't use for itself
> or knows it wants to share. Whereas now you want such a
> resource controlled first by Dom0, and only then handed to Xen.
> So yes, Dom0 would need to zap any mappings of these pages
> (and Xen would need to verify that, which would come mostly
> without new code as long as struct page_info gets properly
> used for all this memory) before Xen could use it. Much like
> ballooning out a normal RAM page.
>
Thanks, I'll look into this balloon approach.
Haozhong
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next prev parent reply other threads:[~2016-03-17 8:58 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 [this message]
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
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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