Re: Enhancing Xen's Kconfig infrastructure to support tailored solutions

[Wei Liu <wei.liu2@citrix.com>]

On Thu, Feb 14, 2019 at 09:03:24PM +0000, Lars Kurth wrote:
> 
> 
> > On 14 Feb 2019, at 18:32, Stefano Stabellini <sstabellini@kernel.org> wrote:
> > 
> > On Thu, 14 Feb 2019, Jan Beulich wrote:
> >>>>> On 13.02.19 at 20:11, <sstabellini@kernel.org> wrote:
> >>> On Wed, 13 Feb 2019, Wei Liu wrote:
> >>>> On Tue, Feb 12, 2019 at 09:34:25PM -0500, Daniel P. Smith wrote:
> >>>>> Greetings,
> >>>>> 
> >>>>> On the 11/14/18 Xen x86 community call a discussion was initiated about
> >>>>> using Kconfig to build minimized versions of Xen for security, safety
> >>>>> and other certification requirements. After some offline discussions
> >>>>> with Xen contributors I realized that a variety of efforts each with
> >>>>> their own respective goals are underway,
> >>>>> 
> >>>>> - nested virtualization
> >>>>> - mixed criticality architectures
> >>>>> - reducing trusted componentary
> >>>>> - combining hardware protection of virtualization with performance and
> >>>>> ease-of-use of containers
> >>>>> 
> >>>>> These efforts use hypervisors in different roles, all which Xen is
> >>>>> capable of meeting. Today Xen's utility comes at the expense of carrying
> >>>>> features necessary for one role to be present in another role where it
> >>>>> is not required, e.g. PV interfaces that may not be essential in an ARM
> >>>>> mixed criticality deployment.
> >>>>> 
> >>>>> The initial focus will be to explore and document the range of possible
> >>>>> use cases that are of interest to the Xen community. This will be the
> >>>>> input to a design document that is crafted in conjunction with the Xen
> >>>>> maintainers, to identify possible approaches to extend the existing
> >>>>> Kconfig infrastructure to produce tailored instances of Xen.
> >>>>> 
> >>>>> If you are interested in participating in this effort, please reply to
> >>>>> this thread to outline possible use cases, design constraints and other
> >>>>> considerations for improving Xen's Kconfig infrastructure to support
> >>>>> tailoring for specific use cases.
> >>>>> 
> >>>> 
> >>>> My impression from the community call is that you want to provide
> >>>> smallish configurations for different use cases.
> >>>> 
> >>>> The Kconfig infrastructure is already able to do what you want as far as
> >>>> I can tell.  You can easily feed it a base config file -- see files
> >>>> under automation/configs/x86/.  What sort of extension is needed in your
> >>>> opinion?
> >>>> 
> >>>> As use case goes, it would be a good start if you just submit something
> >>>> you care about.
> >>> 
> >>> I mentioned on the call that a good first start could be a kconfig that
> >>> allows to build an hypervisor binary with only support for PVH and only
> >>> support for recent Intel machines, with the goal of minimizing the code
> >>> base to less than 100K LOC.
> >> 
> >> "With only support for PVH" (which really means HVM) we already have.
> >> "With only support for recent Intel machines" would require adding new
> >> Kconfig options first, to control Intel, AMD, etc separately, and to then
> >> further somehow separate "old" from "new" (which may turn out not
> >> very easy to do without a lot of #ifdef-ary or other code churn). I'm
> >> not aware of something like this existing on Linux either - all I'm aware
> >> of there is a means to control what -m<arch> option might be passed
> >> to the compiler, but without disabling any source code from getting
> >> compiled.
> > 
> > I was thinking along the lines of having options to disable drivers for
> > older timers and older interrupt controllers that are not needed on
> > recent machines.
> > 
> > 
> >> And then "with only support for recent Intel machines" could also imply
> >> HAP-only; disabling shadow code (which also is already possible) will
> >> alone save almost 10k LOC (counting .c files only).
> > 
> > I have just run `make cloc' on x86 with the smallest possible
> > configuration (HVM only):
> > 
> > 
> > http://cloc.sourceforge.net <http://cloc.sourceforge.net/> v 1.60  T=0.87 s (370.3 files/s, 255808.4 lines/s)
> > -------------------------------------------------------------------------------
> > Language                     files          blank        comment           code
> > -------------------------------------------------------------------------------
> > C                              309          33238          29432         157001
> > Assembly                        14            466            531           2435
> > -------------------------------------------------------------------------------
> > SUM:                           323          33704          29963         159436
> > -------------------------------------------------------------------------------
> > 
> > This is great! The last time I did the count it was above 220K LOC.  We
> > should make more noise about this -- it is a major.
> 
> @Wei: the binary size data is not that impressive. Would it be possible to do the make cloc on HVM, PV and mixed?
> I can include this into the PR for 4.12. Sorry for slightly hi-jacking the thread.

Not sure how Stefano got the 157k number. Here are some results from
staging.


* Full build

cloc --list-file=/tmp/tmp.sSYTTwC8vo
     368 text files.
     359 unique files.
       6 files ignored.

github.com/AlDanial/cloc v 1.70  T=0.73 s (489.4 files/s, 342664.7 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              336          35990          32543         174886
Assembly                        19            700            918           3534
-------------------------------------------------------------------------------
SUM:                           355          36690          33461         178420
-------------------------------------------------------------------------------
rm /tmp/tmp.sSYTTwC8vo

* HVM only with shadow

cloc --list-file=/tmp/tmp.dr9H29oAjZ
     350 text files.
     341 unique files.
       6 files ignored.

github.com/AlDanial/cloc v 1.70  T=0.70 s (481.2 files/s, 345675.6 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              319          35114          31729         170552
Assembly                        18            665            857           3188
-------------------------------------------------------------------------------
SUM:                           337          35779          32586         173740
-------------------------------------------------------------------------------
rm /tmp/tmp.dr9H29oAjZ


* PV only with shadow

cloc --list-file=/tmp/tmp.iFlA6cYriw
     307 text files.
     300 unique files.
       5 files ignored.

github.com/AlDanial/cloc v 1.70  T=0.59 s (502.7 files/s, 338427.3 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              280          28300          26343         140419
Assembly                        17            658            848           3386
-------------------------------------------------------------------------------
SUM:                           297          28958          27191         143805
-------------------------------------------------------------------------------
rm /tmp/tmp.iFlA6cYriw


* HVM only without shadow

cloc --list-file=/tmp/tmp.xX9DEaEw14
     346 text files.
     339 unique files.
       5 files ignored.

github.com/AlDanial/cloc v 1.70  T=0.69 s (487.1 files/s, 344973.4 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              318          34576          30963         167736
Assembly                        18            665            857           3188
-------------------------------------------------------------------------------
SUM:                           336          35241          31820         170924
-------------------------------------------------------------------------------
rm /tmp/tmp.xX9DEaEw14


* PV only without shadow

cloc --list-file=/tmp/tmp.w2YYkxG90d
     302 text files.
     299 unique files.
       3 files ignored.

github.com/AlDanial/cloc v 1.70  T=0.62 s (484.2 files/s, 319189.4 lines/s)
-------------------------------------------------------------------------------
Language                     files          blank        comment           code
-------------------------------------------------------------------------------
C                              280          27835          25697         137998
Assembly                        18            660            848           3395
-------------------------------------------------------------------------------
SUM:                           298          28495          26545         141393
-------------------------------------------------------------------------------
rm /tmp/tmp.w2YYkxG90d

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