Re: [Xen-devel] [GSoc] GSoc Introduction : Xen on ARM: create multiple guests from device tree

[Stefano Stabellini <sstabellini@xxxxxxxxxx>]

On Mon, 3 Apr 2017, Methuku Karthik wrote:
> Hi Stefano,
> 
> I have asked questions in inline. Clarification below questions would really 
> help me in contribution. Please look into the questions. I am highlighting 
> them in this mail.

Hi Methuku,

please do not use HTML in emails.


>  For example, Dom1 should be able to share a page with Dom2 and a
>   different page with Dom3. It needs to be clear which page is shared with
> which VM from the VM config files.
> 
>  
> when we create vms using xl create , for example if i am planning create 
> three VMs,
> 
> Dom1, Dom2 and Dom3, because of the page sharing are we imposing any order of
>   creating VMs.
> 
>   I am asking this question to clarify this point, while creation of Dom1 if 
> its
>   sharing pages with Dom 2 and Dom 3 , should Xen already be aware of Dom2 
> and Dom3?

I don't think so. The user should be able to share the same page even
with Dom4 when it comes along.



>   I am referring to following links to understand about mem sharing.
> 
>   
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/tests/mem-sharing/memshrtoo
>   l.c;h=8e5e22b9e95d91f1441d8eb226b64852eca075d5;hb=HEAD
>   http://xenbits.xen.org/docs/unstable/misc/grant-tables.txt
> 
>   I also want to figure out how domains are created and how xl tool parses 
> the file
>   and passes on the information to domain creation . Let me know if i am 
> thinking in
>   right direction.

I think we won't be able to use the grant table for this. The toolstack
will have to manually map a given page of one guest to another guest.


>   suggest any resource or work which would help with designing config file 
> options.

Look at the existing xl config file options which are described on the
man page.


>  I will start with Xen-38 that would help me in exploring init code. Correct 
> me if i
>   am wrong.

XEN-38 is a good start but it's actually only a build change.


>   I have a few questions and clarifications before proceeding further. I have 
> checked
>   how config.gz file is generated in linux kernel source.
>   In linux kernel sources, if CONFIG_IKCONFIG_PROC option is set, .conifg 
> file which
>   is generated after choosing options with lets say from make menuconfig  is 
> read into
>   a variable, this way its part of build.
> 
>   during init time proc_create service is used to create this file config.gz.
>   http://lxr.free-electrons.com/source/kernel/configs.c
> 
> 
>   I guess i have to do something similar.
> 
>   Questions :
> 
>   1. When Xen is build using the make command, we effectively set 
> XEN_COMPILE_ARCH,
>   XEN_OS, XEN_TARGET which allow using corresponding .mk file from config 
> folder.
>   These variable in turn decide what are the config options. I wasnt able to 
> find any
>   .config. Please direct me to find the file or if i am missing something. 

Give a look at xen/.config, that is the file we would like to embed into
the xen binary. Probably it would need to be included in an header file
and become a very long char[].


>   2. Where and how this config file should be accessible to  User once in 
> Dom0. Is the
>   xen folder created to keep the information about guest domains like proc 
> for process
>   in linux kernel ? Will that be suitable location to have config file.

One option is to export it as a new hypercall. That would be great, but
I think that is beyond the scope of a small inital code contribution.

What we would like is to be able to extract the .config from a xen
binary manually, for example using the "strings" command. Let's supposed
that a user is running Xen and finds a bug. We asked her to provide us
with her Xen binary. We get the binary and from it we extract the
.config.


>   3. if i assume that i will approach similarly, i have to add services to be 
> called
>   during init stage. As am not acquainted with code base, i could just grep 
> with
>   _start or _init or similar strings to find out initialization code. Any
>   input(function name or filename) to look for will be of great help.
>
> On Mon, Apr 3, 2017 at 3:35 PM, Stefano Stabellini <sstabellini@xxxxxxxxxx> 
> wrote:
>       Thank you! I am looking forward to your contribution on the list! If you
>       encounter any issues, please let us know.
> 
>       The code contribution is more important, but if you find the time in the
>       next few days, it would be nice to add more details to the
>       implementation plan, such as where the memory gets allocated, whether it
>       is taken from a VM, and if so, which one. Also what kind of "token"
>       could be used in the config option and how the toolstack could keep
>       track of the token - memory page references.
> 
>       Thanks,
> 
>       Stefano
> 
>       On Mon, 3 Apr 2017, Methuku Karthik wrote:
>       > Hi Stefano,
>       >
>       > Thanks for Input. I was not able to spend enough time last couple of 
> weeks due to
>       > projects. I have received mail from Lars Kurt explaining submission 
> of draft
>       > proposal and possibility to work on micro tasks.
>       >
>       > I have created a draft proposal from with your inputs and what i 
> learnt about
>       > sharing pages and memory management in Xen, please access it from here
>       >
>       > 
> https://docs.google.com/document/d/1xLmR7x4yfCbRgpuefZQNhZ4lAu-6slW0oXPmjnxcnz0/edi
>       > t#heading=h.1yvc35w6t3fu
>       >
>       > I haven't written anything about maintenance. I have included some 
> links i thought
>       > will be helpful under references and referenced wherever applicable.
>       >
>       > Please suggest comments and inputs.
>       >
>       > On Tue, Mar 28, 2017 at 8:12 PM, Stefano Stabellini 
> <sstabellini@xxxxxxxxxx> wrote:
>       > > CC'ing a couple of maintainers that might have more insights on this
>       > > project.
>       > >
>       > > On Tue, 28 Mar 2017, Stefano Stabellini wrote:
>       > >> On Tue, 28 Mar 2017, Methuku Karthik wrote:
>       > >> > Hi Stefano,
>       > >> >
>       > >> > Kindly suggest me reading material that could help me understand 
> and
>       > >> > come up with the proposal.
>       > >>
>       > >> Sure! For the "Xen on ARM: create multiple guests from device tree"
>       > >> project, the idea is that on many embedded systems the user knows 
> how
>       > >> many guests to create beforehand, and usually it is a small 
> number, like
>       > >> 2 or 3. Often these guests don't even have any PV frontends, but 
> just a
>       > >> set of devices assigned to them. An example could be an extremely 
> simple
>       > >> guest that only accesses one physical device (which is assigned to 
> it at
>       > >> boot) and prints messages using the debug hypercalls (see
>       > >> xen/arch/arm/traps.c:do_debug_trap).
>       > >>
>       > >> In this scenario, there is no need to wait for Dom0 to boot to 
> create
>       > >> this second guest (I'll call it Dom1, to distinguish it from 
> Dom0). Xen
>       > >> could actually create it directly by itself, the same way it 
> starts Dom0
>       > >> (see xen/arch/arm/domain_build.c:construct_dom0 and
>       > >> docs/misc/arm/device-tree/booting.txt).
>       > >>
>       > >> The project is about extending the existing device interface to 
> pass an
>       > >> additional kernel, initrd, command line arguments for the second 
> virtual
>       > >> machine. It would also need to include which devices should be 
> assigned
>       > >> to it. In response, Xen should build the second VM the same way it 
> would
>       > >> do normally when done via the toolstack (xl/libxl), but it would 
> happen
>       > >> at boot time, before Dom0 is fully up and running.
>       > >>
>       > >>
>       > >>
>       > >> For the "Share a page in memory from the VM config file" project,
>       > >
>       > > Ops, I forgot to add this description :-)
>       > >
>       > > I was saying, for the "Share a page in memory from the VM config 
> file"
>       > > project, the idea is that we want to share a page in memory between 
> two
>       > > VMs just by adding one line to their VM config files. They should be
>       > > able to communicate with each others straight away by writing at the
>       > > right address in memory. That way, even small embedded systems with 
> no
>       > > xenstore support can still setup a communication channel with each
>       > > others.
>       > >
>       > > Fundamentally, it just requires the xl/libxl toolstack (see 
> tools/xl and
>       > > tools/libxl) to parse a new VM config file option, and in response 
> share
>       > > a page at the specified address, or map a page at a specified 
> address.
>       > > If the memory address is wrong, the toolstack needs to be able to 
> handle
>       > > the failure. Sharing pages and mapping pages in xl/libxl is easy; 
> the
>       > > difficulty of the project is coming up with the right parameter in 
> the
>       > > VM config file so that multiple VMs can share different pages with 
> each
>       > > others. It probably requires the introduction of a "token" to 
> identify
>       > > the page you want to share across multiple VM config files.
>       > >
>       > > For example, Dom1 should be able to share a page with Dom2 and a
>       > > different page with Dom3. It needs to be clear which page is shared 
> with
>       > > which VM from the VM config files.
>       > >
>       > when we create vms using xl create , for example if i am planning 
> create three VMs,
>       >
>       > Dom1, Dom2 and Dom3, because of the page sharing are we imposing any 
> order of
>       > creating VMs.
>       >
>       > I am asking this question to clarify this point, while creation of 
> Dom1 if its
>       > sharing pages with Dom 2 and Dom 3 , should Xen already be aware of 
> Dom2 and Dom3?
>       >
>       > I am referring to following links to understand about mem sharing.
>       >
>       > 
> http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/tests/mem-sharing/memshrtoo
>       > l.c;h=8e5e22b9e95d91f1441d8eb226b64852eca075d5;hb=HEAD
>       > http://xenbits.xen.org/docs/unstable/misc/grant-tables.txt
>       >
>       > I also want to figure out how domains are created and how xl tool 
> parses the file
>       > and passes on the information to domain creation . Let me know if i 
> am thinking in
>       > right direction.
>       >
>       > suggest any resource or work which would help with designing config 
> file options.
>       >
>       > >
>       > >
>       > >> > On Tue, Mar 28, 2017 at 1:38 PM, Stefano Stabellini
>       > >> > <sstabellini@xxxxxxxxxx> wrote:
>       > >> > > I would also like to take the opportunity to remind you of the 
> upcoming
>       > >> > > deadline for applications submissions, which is the 3rd of 
> April for
>       > >> > > GSoC, see:
>       > >> > >
>       > >> > > http://marc.info/?l=xen-devel&m=149071502330534
>       > >> > >
>       > >> > > The GSoC application system is
>       > >> > > https://summerofcode.withgoogle.com/get-started/.
>       > >> > >
>       > >> > > Please give a look at the Xen Project application template 
> here:
>       > >> > >
>       > >> > > 
> https://wiki.xenproject.org/wiki/GSoC_Student_Application_Template
>       > >> > >
>       > >> > > It also includes an "Implementation Plan", where you have the 
> chance to
>       > >> > > explain the implementation plan for the projects you would 
> like to apply
>       > >> > > for. You can apply for more than one project if you want to.
>       > >> >
>       > >> > Thanks for the reminder Stefano. I will post some questions 
> about my
>       > >> > implementation plan.
>       > >> >
>       > >> > I would like to spend my time fixing the bug but as deadline is
>       > >> > approaching , I would like to know the bare essential expected 
> in the
>       > >> > proposal?
>       > >>
>       > >> It needs to include the basic milestones and how long you estimate 
> it is
>       > >> going to take to complete each of them. More details you add, more
>       > >> you'll show your understanding of the problem.
>       > >>
>       > >>
>       > >> > >
>       > >> > > Thanks,
>       > >> > >
>       > >> > > Stefano
>       > >> > >
>       > >> > >
>       > >> > > On Mon, 27 Mar 2017, Stefano Stabellini wrote:
>       > >> > >> Hello Methuku,
>       > >> > >>
>       > >> > >> It is great to hear that you are interested in working on Xen 
> on ARM.
>       > >> > >> It's good that you already know how to build and install Xen 
> on an ARM
>       > >> > >> board.
>       > >> > >>
>       > >> > >> Do you have serial access to your Nvidia Jetson TK1? If not, 
> I would
>       > >> > >> suggest to setup another test environment based on a 
> different board, or
>       > >> > >> simply use the ARM Foundation Platform which is a free (as in 
> beer)
>       > >> > >> software emulator.
>       > >> > >>
>       > >> > >> In terms of bug fixes, you could give a look at
>       > >> > >>
>       > >> > >> https://xenproject.atlassian.net/projects/XEN/issues
>       > >> > >>
>       > >> > >> Most of the items listed are large projects, but some of them 
> are pretty
>       > >> > >> small, small enough to be a starting point. For example 
> XEN-29 (Add
>       > >> > >> -fstack-protector support to the hypervisor), XEN-30 (Make 
> out-of-tree
>       > >> > >> builds work) or XEN-38 (Xen - Embed .config in Xen binary).
>       > >> >
>       > >> > I  started working on XEN-38 for now. But i am also interested 
> to look
>       > >> > into XEN-30.
>       > >>
>       > >> Be careful that XEN-30 is longer than it looks because there are 
> lots of
>       > >> Makefiles to fix. However, even if you don't convert all Makefiles 
> to
>       > >> support out-of-tree builds but only some, it would still be OK.
>       >
>       > I will start with Xen-38 that would help me in exploring init code. 
> Correct me if i
>       > am wrong.
>       >
>       > I have a few questions and clarifications before proceeding further. 
> I have checked
>       > how config.gz file is generated in linux kernel source.
>       > In linux kernel sources, if CONFIG_IKCONFIG_PROC option is set, 
> .conifg file which
>       > is generated after choosing options with lets say from make 
> menuconfig  is read into
>       > a variable, this way its part of build.
>       >
>       > during init time proc_create service is used to create this file 
> config.gz.
>       > http://lxr.free-electrons.com/source/kernel/configs.c
>       >
>       >
>       > I guess i have to do something similar.
>       >
>       > Questions :
>       >
>       > 1. When Xen is build using the make command, we effectively set 
> XEN_COMPILE_ARCH,
>       > XEN_OS, XEN_TARGET which allow using corresponding .mk file from 
> config folder.
>       > These variable in turn decide what are the config options. I wasnt 
> able to find any
>       > .config. Please direct me to find the file or if i am missing 
> something. 
>       >
>       > 2. Where and how this config file should be accessible to  User once 
> in Dom0. Is the
>       > xen folder created to keep the information about guest domains like 
> proc for process
>       > in linux kernel ? Will that be suitable location to have config file.
>       >
>       > 3. if i assume that i will approach similarly, i have to add services 
> to be called
>       > during init stage. As am not acquainted with code base, i could just 
> grep with
>       > _start or _init or similar strings to find out initialization code. 
> Any
>       > input(function name or filename) to look for will be of great help.
>       >
>       > Best,
>       > Karthik.
>       >
>       > >>
>       > >>
>       > >> > >> Cheers,
>       > >> > >>
>       > >> > >> Stefano
>       > >> > >>
>       > >> > >>
>       > >> > >> On Mon, 27 Mar 2017, Methuku Karthik wrote:
>       > >> > >> > Hi Everyone,
>       > >> > >> >
>       > >> > >> > My name is Karthik. I am a first year graduate student in 
> Embedded Systems
>       > at University of Pennsylvania. I am avid c, c++ and python 
> programmer.I have 4 years
>       > of
>       > >> > >> > work experience as Embedded Software developer at Airbus.
>       > >> > >> >
>       > >> > >> > For the last four months I have been working as a research 
> assistant in
>       > PRECISE lab at the University of Pennsylvania, helping Meng Xu 
> (cc.ed) to evaluate
>       > the
>       > >> > >> > performance of the Xen's RTDS scheduler.
>       > >> > >> >
>       > >> > >> > I'm interested in the following two projects. I'm happy to 
> work on one of
>       > them.
>       > >> > >> > (1) Share a page in memory from the VM config file.
>       > >> > >> > (2)  Xen on ARM: create multiple guests from device tree.
>       > >> > >> >
>       > >> > >> > I have experience in compiling Xen and installing it on ARM 
> board(Nvidia
>       > Jetson TK1). I'm also well equiped in using the xl tool to manage the 
> VMs.
>       > >> > >> >
>       > >> > >> > I noticed that I should contribute some bug fixes to be 
> able to get the
>       > ticket to the Xen GSoC.
>       > >> > >> > Do you have some suggestions on how I should start?
>       > >> > >> > Do you have a list of simple bugs that I can fix?
>       > >> > >> >
>       > >> > >> > I'm very interested in the Xen Project. I want to become a 
> Xen contributor
>       > in the near future.
>       > >> > >> >
>       > >> > >> > Thank you very much for your help!
>       > >> > >> >
>       > >> > >> > Best,
>       > >> > >> > Karthik
>       > >> > >> >
>       > >> > >> >
>       > >> >
>       > >> > Best,
>       > >> > Karthik.
>       > >> >
>       > >>
>       >
>       >
>       >
> 
> 
> 
>

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