Question about starting a domain

Question about starting a domain

[Kathy Chen]

Sorry about my previous uncompleted message.

I installed the latest Xen with linux-2.6.8.1 on
my RedHat machine today. After "make-install" and
restart, it runs well. When I edited the xmexample1
file at minimun, including "kernel", "memory", "disk",
"dhcp", and executed "xm create -f ./xmexample1
vmid=1", there's an error. It says 
      "Error: Internal Server Error"

"xm list" shows the status of domain 1 is paused.
And command "xm destroy 1" has the same error: "Error:
Internal Server Error". My xmexample1 file is roughly
like this:
    kernel="/boot/vmlinuz-2.6.8.1-xenU"
    memory=64
    disk=[ 'phy:hda2,hda2,w' ]
    ip='x.x.x.x'
    netmask='x.x.x.x'
    gateway='x.x.x.x'
    hostname="x.x.x"
    root="/dev/hda2 ro"
I have a partition /dev/hda2 installed with RedHat to
work as domain 1.


Thanks for your help.
Kathy


		
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Re: Question about starting a domain

[Steven Hand]

>I installed the latest Xen with linux-2.6.8.1 on
>my RedHat machine today. After "make-install" and
>restart, it runs well. When I edited the xmexample1
>file at minimun, including "kernel", "memory", "disk",
>"dhcp", and executed "xm create -f ./xmexample1
>vmid=1", there's an error. It says 
>      "Error: Internal Server Error"

Have you started xend? ("xend start") 
I guess you have, but in this case I'd expect a load of 
output from xend after you type 'xm create...' - do you 
see anything?

One other thing to check is you have a /etc/xen/xmdefconfig 
(or to simply cp xmexampl to /etc/xen/xmdefconfig and then 
 try "xm create -c vmid=") 

cheers,

S.



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Re: Question about starting a domain

[Kathy Chen]

Thanks, Steven.
I did start the xend, and "Error: Internal Server
Error" is the only output of "xm create ...".

But after I copied the config file to
/etc/xen/xmdefconfig, and used "xm create -c
vmid=...". It works now!

Thanks.
Kathy

--- Steven Hand <Steven.Hand@cl.cam.ac.uk> wrote:

> 
> >I installed the latest Xen with linux-2.6.8.1 on
> >my RedHat machine today. After "make-install" and
> >restart, it runs well. When I edited the xmexample1
> >file at minimun, including "kernel", "memory",
> "disk",
> >"dhcp", and executed "xm create -f ./xmexample1
> >vmid=1", there's an error. It says 
> >      "Error: Internal Server Error"
> 
> Have you started xend? ("xend start") 
> I guess you have, but in this case I'd expect a load
> of 
> output from xend after you type 'xm create...' - do
> you 
> see anything?
> 
> One other thing to check is you have a
> /etc/xen/xmdefconfig 
> (or to simply cp xmexampl to /etc/xen/xmdefconfig
> and then 
>  try "xm create -c vmid=") 
> 
> cheers,
> 
> S.
> 
> 



	
		
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Re: Question about starting a domain

[Ian Pratt]

> Thanks, Steven.
> I did start the xend, and "Error: Internal Server
> Error" is the only output of "xm create ...".
> 
> But after I copied the config file to
> /etc/xen/xmdefconfig, and used "xm create -c
> vmid=...". It works now!

Kathy,

Are you saying that the exact same config and invocation worked
when you renamed it to xmdefconfig but didn't when you specified
the config file using the -f option? It's pretty hard to see how
that could happen.

It would be useful to see the output of these two invocations so
that we can fix the bug.

Thanks,
Ian




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Re: Question about starting a domain

[Kathy Chen]

Ian,

Yes, I used the exact same config file.
First time I put it into xeno-unstable.bk directory,
and used: 
    xm create -f /root/xeno-unstable.bk/xmexample1 -c
vmid=1
The only output is 
    "Error: Internal Server Error"
With "xm list" I can see that the newly created domain
is there, with state "paused".

And second time, I copied it into /etc/xen/, renamed
it to xmdefconfig, and used: 
    xm create -c vmid=1
Everything works well I think, with reasonable output.
I can ssh into the newly created domain. 

But right now I can't repeat the error. The first case
  also works. I didn't change the system settings,
without using "bk pull", but restarted the system
several times.

Thanks.
Kathy
> Kathy,
> 
> Are you saying that the exact same config and
> invocation worked
> when you renamed it to xmdefconfig but didn't when
> you specified
> the config file using the -f option? It's pretty
> hard to see how
> that could happen.
> 
> It would be useful to see the output of these two
> invocations so
> that we can fix the bug.
> 
> Thanks,
> Ian
> 
> 
> 



		
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Xen reboots when trying to start new domain

[Kip Macy]

I'm running what was 1.1301 at the time of the clone (xen.bkbits.net
indicates that it is now 1.1280.1.21) on a dual opteron with 8GB
running in 32-bit mode.

title Xen 1.1301 / XenoLinux 2.6.8.1
        kernel /xen-1.1301.gz dom0_mem=262144 com1=9600,8n1 pdb=com1H console=com1 noreboot
        module /vmlinuz-1.1301 root=/dev/hda3 ro



The FreeBSD domain builder works fine running against 1.1229, however,
on the more recent snapshot the following occurs:

in my login:

r xm create -f /u/kmacy/xentmp/freebsd.curly -c
name=xen-vm0.lab.netapp.com image=/u/kmacy/kernel vmid=10
Using config file "/u/kmacy/xentmp/freebsd.curly".
config: (vm (name xen-vm0.lab.netapp.com) (memory 16) (cpu 10) (image
(freebsd (kernel /u/kmacy/kernel) (args
'boot.netif.ip=172.16.9.213,boot.netif.netmask=255.255.255.0,vfs.root.mountfrom=ufs:/dev/xbd0a,bootverbose=1')))
(device (vbd (uname phy:loopa) (dev loopa) (mode w))) (device (vif (mac
aa:00:00:7e:d7:73))))
ERROR: Failure when submitting mmu updates: Invalid argument
requestReceived> No device: Message type
netif_be_driver_status_changed_t 3:32 <Channel dom=0 ports=2:-1>
vif-bridge up vif=vif1.0 domain=xen-vm0.lab.netapp.com
mac=aa:00:00:7e:d7:73 bridge=xen-br0
<logout>

on the console:
XEN) (file=sched_bvt.c, line=367) Get domain 1 bvt mcu_adv=10,
warpback=0, warpvalue=0, warpl=2000000000, warpu=1000000000^M
(XEN) (file=sched_bvt.c, line=400) Get domain 1 bvt mcu_adv=10,
warpback=0, warpvalue=0, warpl=2000000000000000, warpu=1000000000000000^M
(XEN)
(file=/t/niners/users/xen/xeno-unstable.bk.work.1.1301/xen/include/asm/mm.h,
line=241) Bad type (saw 40000000 != exp 25fe0000) for pfn 000035b5^M
(XEN) DOM0: (file=memory.c, line=317) Bad page type for pfn 000035b5
(40000001)^M
(XEN)
(file=/t/niners/users/xen/xeno-unstable.bk.work.1.1301/xen/include/asm/mm.h,
line=254) Unexpected va backpointer (saw 30000001 != exp 26000000) for pfn 000035b6^M
(XEN) DOM0: (file=memory.c, line=317) Bad page type for pfn 000035b6
(30000001)^M
(XEN) DOM0: (file=memory.c, line=347) Attempt to create linear p.t. with
write perms^M
(XEN)
(file=/t/niners/users/xen/xeno-unstable.bk.work.1.1301/xen/include/asm/mm.h,
line=280) Error while validating pfn 000035b5 for type 40000000. caf=60000002 taf=40000001^M
(XEN) DOM0: (file=memory.c, line=317) Bad page type for pfn 000035b5
(40000000)^M
(XEN) DOM0: (file=memory.c, line=849) Error while pinning pfn 000035b5^M
(XEN)
(file=/t/niners/users/xen/xeno-unstable.bk.work.1.1301/xen/include/asm/mm.h,
line=158) Error pfn 000035b5: ed=fc5cb340, sd=00000001, caf=60000000, taf=40000000^M
<reboot>
Phoenix ServerBIOS 3 Release 6.0     ^[[0;30;40m
^[[\
2;1H^[[0;37;40mCopyright 1985-2002 Phoenix Technologies Ltd.^[[0;30;40m
^[[3;\
1H^[[0;37;40mAll Rights Reserved^[[0;30;40m
^[[4;1H\
^[[0;37;40mHDAMA Ver 1.84^[[0;30;40m
^[[5;1H^[\
[0;37;40mBuild Time: 01/07/04 15:51:10^[[0;30;40m
^[[6;1H^[[0\
;37;40m                       ^[[0;30;40m
^[[7;1H^[[0;37;40m                           \
  Rhapsody Mainboard      ^[[0;30;40m
^[[8;1H^[[0;37;40m                               \
    HDAMA             ^[[0;30;40m
^[[9;1H^[[0;37;40m                       ^[[0;30;40m \
                        ^[[10;1H^[[0;37;40mCPU = AMD Opteron(tm)
Processor 242^[[0;30;40m                      \
                       ^[[11;1H^[[0;37;40m2 Processors
Detected^[[0;30;40m                                     \
                      ^[[12;1H^[[0;37;40m579M System RAM
Passed^[[0;30;40m
                    ^[[13;1H
^M
************ REMOTE CONSOLE EXITED *****************^M


It looks like a bug has bug has been introduced in the page checking
logic some time since 1.1229.


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Re: Xen reboots when trying to start new domain

[Keir Fraser]

> 
> I'm running what was 1.1301 at the time of the clone (xen.bkbits.net
> indicates that it is now 1.1280.1.21) on a dual opteron with 8GB
> running in 32-bit mode.
> 
> title Xen 1.1301 / XenoLinux 2.6.8.1
>         kernel /xen-1.1301.gz dom0_mem=262144 com1=9600,8n1 pdb=com1H console=com1 noreboot
>         module /vmlinuz-1.1301 root=/dev/hda3 ro
> 
> 
> 
> The FreeBSD domain builder works fine running against 1.1229, however,
> on the more recent snapshot the following occurs:
> 
> in my login:

Does your builder try to map a page table at more than one place in
the initial page directory (e.g., to provide FreeBSD with a
start-of-day mapping of its memory starting at zero)?

That isn't allowed any more. :-)

 -- Keir


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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

> That isn't allowed any more. :-)

Ahh - yes I think it does. I wonder how FreeBSD will fair without that
mapping. Does the aliasing make ref-counting too hard?






>
>  -- Keir
>
>
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> Xen-devel@lists.sourceforge.net
> https://lists.sourceforge.net/lists/listinfo/xen-devel
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Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

We now support direct update of PTEs by guests. To allow this we have
to record which entry in a page directory the page table is mapped
at. This means we can no longer support having the same page table
mapped at differnt PDE indexes.

 -- Keir

> 
> 
> > That isn't allowed any more. :-)
> 
> Ahh - yes I think it does. I wonder how FreeBSD will fair without that
> mapping. Does the aliasing make ref-counting too hard?
> 
> 
> 
> 
> 
> 
> >
> >  -- Keir
> >
> >
> > -------------------------------------------------------
> > This SF.Net email is sponsored by BEA Weblogic Workshop
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> > _______________________________________________
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> > Xen-devel@lists.sourceforge.net
> > https://lists.sourceforge.net/lists/listinfo/xen-devel
> >



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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

Not surprisingly FreeBSD expects those low temporary double mappings to
be there. How do you recommend fixing this without throwing more
pagetables at it that pmap_init will have to garbage collect?

				-Kip





>
> We now support direct update of PTEs by guests. To allow this we have
> to record which entry in a page directory the page table is mapped
> at. This means we can no longer support having the same page table
> mapped at differnt PDE indexes.
>
>  -- Keir
>
> >
> >
> > > That isn't allowed any more. :-)
> >
> > Ahh - yes I think it does. I wonder how FreeBSD will fair without that
> > mapping. Does the aliasing make ref-counting too hard?
> >
> >
> >
> >
> >
> >
> > >
> > >  -- Keir
> > >
> > >
> > > -------------------------------------------------------
> > > This SF.Net email is sponsored by BEA Weblogic Workshop
> > > FREE Java Enterprise J2EE developer tools!
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> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@lists.sourceforge.net
> > > https://lists.sourceforge.net/lists/listinfo/xen-devel
> > >
>
>
>
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Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

Usually the low mappings are only there to bootstrap the OS out of
non-page-table mode. Once you have page tables, most stuff is going to
transition to the high mappings, surely?

If you just remove the low mappings, I wonder how much code would
actually crash. :-)

Anyway, I've checked in code which, rather than rejecting page tables
that are mapped at multiple different VAs, instead marks the page
information that this is the case. When using shadow page tables, and
potentially writable page tables, this might cause a considerable
slowdown. But that isn't the case for FreeBSD right now of course, so
you could leave teh low mappings for now and strip them out later.

 -- Keir

> Not surprisingly FreeBSD expects those low temporary double mappings to
> be there. How do you recommend fixing this without throwing more
> pagetables at it that pmap_init will have to garbage collect?
> 
> 				-Kip
> 
> 
> 
> 
> 
> >
> > We now support direct update of PTEs by guests. To allow this we have
> > to record which entry in a page directory the page table is mapped
> > at. This means we can no longer support having the same page table
> > mapped at differnt PDE indexes.
> >
> >  -- Keir
> >
> > >
> > >
> > > > That isn't allowed any more. :-)
> > >
> > > Ahh - yes I think it does. I wonder how FreeBSD will fair without that
> > > mapping. Does the aliasing make ref-counting too hard?
> > >
> > >
> > >
> > >
> > >
> > >
> > > >
> > > >  -- Keir
> > > >
> > > >
> > > > -------------------------------------------------------
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> > > > _______________________________________________
> > > > Xen-devel mailing list
> > > > Xen-devel@lists.sourceforge.net
> > > > https://lists.sourceforge.net/lists/listinfo/xen-devel
> > > >
> >
> >
> >
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Re: Re: Xen reboots when trying to start new domain

[Ronald G. Minnich]

On Thu, 9 Sep 2004, Kip Macy wrote:

> Not surprisingly FreeBSD expects those low temporary double mappings to
> be there. How do you recommend fixing this without throwing more
> pagetables at it that pmap_init will have to garbage collect?

I got rid of all the double mapping in Plan 9 by having the loader do a 
bit more work. I no longer remember freebsd startup very well but this 
might be worth a look -- see how much more work the os loader can do to 
set things up, then just start freebsd in the high virtual addresses.

ron


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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

For the moment I'm happy burning an extra page. I was already burning a
page for the start of day stack - now I'm burning 2 pages. GC'ing them
shouldn't be hard.

				-Kip

> I got rid of all the double mapping in Plan 9 by having the loader do a
> bit more work. I no longer remember freebsd startup very well but this
> might be worth a look -- see how much more work the os loader can do to
> set things up, then just start freebsd in the high virtual addresses.
>
> ron
>
>
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world doesn't compile with debug enabled

[Kip Macy]

gcc -nostdinc -fno-builtin -fno-common -fno-strict-aliasing -O3 -
Wall -Werror -fomit-frame-pointer -pipe -I/t/niners/users/xen/xen
1300/xen/include -Wno-pointer-arith -Wredundant-decls -msoft-floa
VERBOSE -DXEN_DEBUGGER -c memory.c -o memory.o
cc1: warnings being treated as errors
memory.c: In function `ptwr_status':
memory.c:1924: warning: too many arguments for format
make[3]: *** [memory.o] Error 1
make[3]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
x86'
make[2]: *** [/t/niners/users/xen/xeno-unstable.bk.work.1.1300/xe
make[2]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
make[1]: *** [all] Error 2
make[1]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
make: *** [world] Error 2


2004/09/08 cl349      |     PTWR_PRINTK(PP_ALL, ("    pl2e %p l2e %08lx pfn %08lx taf %08x/%08x\n",
2004/09/08 cl349      |                          pl2e, l2_pgentry_val(*pl2e), l1_pgentry_val(
2004/09/08 cl349      |                              linear_pg_table[(unsigned long)pl2e >>
2004/09/08 cl349      |                              PAGE_SHIFT]) >> PAGE_SHIFT,
2004/09/08 cl349      |                          frame_table[2004/09/08 cl349      | l2_pgentry_to_pagenr(*pl2e)].u.inuse.type_info,
2004/09/08 cl349      |                          frame_table[pfn].u.inuse.type_info,
2004/09/08 cl349      |                          frame_table[pfn].u.inuse.domain->domain));



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Re: world doesn't compile with debug enabled

[Keir Fraser]

Now fixed.

 K.

> 
> gcc -nostdinc -fno-builtin -fno-common -fno-strict-aliasing -O3 -
> Wall -Werror -fomit-frame-pointer -pipe -I/t/niners/users/xen/xen
> 1300/xen/include -Wno-pointer-arith -Wredundant-decls -msoft-floa
> VERBOSE -DXEN_DEBUGGER -c memory.c -o memory.o
> cc1: warnings being treated as errors
> memory.c: In function `ptwr_status':
> memory.c:1924: warning: too many arguments for format
> make[3]: *** [memory.o] Error 1
> make[3]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
> x86'
> make[2]: *** [/t/niners/users/xen/xeno-unstable.bk.work.1.1300/xe
> make[2]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
> make[1]: *** [all] Error 2
> make[1]: Leaving directory `/t/niners/users/xen/xeno-unstable.bk.
> make: *** [world] Error 2
> 
> 
> 2004/09/08 cl349      |     PTWR_PRINTK(PP_ALL, ("    pl2e %p l2e %08lx pfn %08lx taf %08x/%08x\n",
> 2004/09/08 cl349      |                          pl2e, l2_pgentry_val(*pl2e), l1_pgentry_val(
> 2004/09/08 cl349      |                              linear_pg_table[(unsigned long)pl2e >>
> 2004/09/08 cl349      |                              PAGE_SHIFT]) >> PAGE_SHIFT,
> 2004/09/08 cl349      |                          frame_table[2004/09/08 cl349      | l2_pgentry_to_pagenr(*pl2e)].u.inuse.type_info,
> 2004/09/08 cl349      |                          frame_table[pfn].u.inuse.type_info,
> 2004/09/08 cl349      |                          frame_table[pfn].u.inuse.domain->domain));
> 



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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

> >
> >
> >
> > The FreeBSD domain builder works fine running against 1.1229, however,
> > on the more recent snapshot the following occurs:
> >
> > in my login:
>
> Does your builder try to map a page table at more than one place in
> the initial page directory (e.g., to provide FreeBSD with a
> start-of-day mapping of its memory starting at zero)?


That doesn't give Xen license to reboot does it?




>
> That isn't allowed any more. :-)
>
>  -- Keir
>
>
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Re: Xen reboots when trying to start new domain

[Keir Fraser]

> > 
> > I'm running what was 1.1301 at the time of the clone (xen.bkbits.net
> > indicates that it is now 1.1280.1.21) on a dual opteron with 8GB
> > running in 32-bit mode.
> > 
> > title Xen 1.1301 / XenoLinux 2.6.8.1
> >         kernel /xen-1.1301.gz dom0_mem=262144 com1=9600,8n1 pdb=com1H console=com1 noreboot
> >         module /vmlinuz-1.1301 root=/dev/hda3 ro
> > 
> > 
> > 
> > The FreeBSD domain builder works fine running against 1.1229, however,
> > on the more recent snapshot the following occurs:
> > 
> > in my login:
> 
> Does your builder try to map a page table at more than one place in
> the initial page directory (e.g., to provide FreeBSD with a
> start-of-day mapping of its memory starting at zero)?
> 
> That isn't allowed any more. :-)
> 
>  -- Keir

The crash is potentially interesting. Your output looks as though
there was no crash dump before rebooting - a sure sign of a triple
fault. However, they are very rare indeed. Is it possible you lost any
console output? For example, BIOS/GRUB screens sometimes erase parts
of a serial dump in an effort to 'draw' themselves. :-)

How would the FreeBSD builder react to a one of its mmu_update
requests failing?

 -- Keir


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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

> The crash is potentially interesting. Your output looks as though
> there was no crash dump before rebooting - a sure sign of a triple
> fault. However, they are very rare indeed. Is it possible you lost any
> console output? For example, BIOS/GRUB screens sometimes erase parts
> of a serial dump in an effort to 'draw' themselves. :-)

Everything I saw on the screen was in the e-mail. After the failure it
hangs for a moment then it resets (in spite of being passed noreboot).


>
> How would the FreeBSD builder react to a one of its mmu_update
> requests failing?

The domain builder just passes the error up to the caller:

<snip>
    ctxt->cpu_ctxt.esi = VADDR(KPTDI, startinfopa); /* start info mapped
address */
    ctxt->cpu_ctxt.eax = PTOM(IdlePTD);
    ctxt->cpu_ctxt.ebx = PTOM(KPTphys);
    ctxt->cpu_ctxt.edi = physindex;

    if (finish_mmu_updates(xc_handle, mmu))
	goto error_out;

    /* index of first free physical page */
    return physindex;
 error_out:
    return -1;

}


			-Kip


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Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

> > The crash is potentially interesting. Your output looks as though
> > there was no crash dump before rebooting - a sure sign of a triple
> > fault. However, they are very rare indeed. Is it possible you lost any
> > console output? For example, BIOS/GRUB screens sometimes erase parts
> > of a serial dump in an effort to 'draw' themselves. :-)
> 
> Everything I saw on the screen was in the e-mail. After the failure it
> hangs for a moment then it resets (in spite of being passed noreboot).

Debugging a triple fault will require a whole load more tracing to be
added. Basically looking for the last moment at which the machine
falls silent and reboots!

 -- Keir


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Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

Right. And then does the builder go right ahead and call
DOM0_BUILDDOMAIN anyway? :-)

The error checking in there is currently rather poor. I shall fix it
up and let you know when I'm done. I'm expecting that this will
prevent the triple fault.

 -- Keir

> The domain builder just passes the error up to the caller:
> 
> <snip>
>     ctxt->cpu_ctxt.esi = VADDR(KPTDI, startinfopa); /* start info mapped
> address */
>     ctxt->cpu_ctxt.eax = PTOM(IdlePTD);
>     ctxt->cpu_ctxt.ebx = PTOM(KPTphys);
>     ctxt->cpu_ctxt.edi = physindex;
> 
>     if (finish_mmu_updates(xc_handle, mmu))
> 	goto error_out;
> 
>     /* index of first free physical page */
>     return physindex;
>  error_out:
>     return -1;
> 
> }
> 
> 
> 			-Kip
> 
> 
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Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

Okay, I pushed some cleanups to BUILDDOMAIN. In particular we now
check that the specified pagetable is in fact a valid pagetable :-D

 -- Keir

> 
> Right. And then does the builder go right ahead and call
> DOM0_BUILDDOMAIN anyway? :-)
> 
> The error checking in there is currently rather poor. I shall fix it
> up and let you know when I'm done. I'm expecting that this will
> prevent the triple fault.
> 
>  -- Keir
> 
> > The domain builder just passes the error up to the caller:
> > 
> > <snip>
> >     ctxt->cpu_ctxt.esi = VADDR(KPTDI, startinfopa); /* start info mapped
> > address */
> >     ctxt->cpu_ctxt.eax = PTOM(IdlePTD);
> >     ctxt->cpu_ctxt.ebx = PTOM(KPTphys);
> >     ctxt->cpu_ctxt.edi = physindex;
> > 
> >     if (finish_mmu_updates(xc_handle, mmu))
> > 	goto error_out;
> > 
> >     /* index of first free physical page */
> >     return physindex;
> >  error_out:
> >     return -1;
> > 
> > }
> > 
> > 
> > 			-Kip
> > 
> > 
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Re: Re: Xen reboots when trying to start new domain

[Ian Pratt]

Kip,

Out of interest, why have you needed to give FreeBSD its own
domain builder rather than use the 'generic ELF' one that Linux
and NetBSD share? (Plan9 has gone with its own builder as it uses
an a.out image format).
 
> Okay, I pushed some cleanups to BUILDDOMAIN. In particular we now
> check that the specified pagetable is in fact a valid pagetable :-D

It's not high on the todo list, but it would be nice to make the
domain builder completely untrusted, and hence be able to
delegate it just the privileges it needs for building a
particular domain. We're not too far away from that. Keir's
changes certainly make it harder for a domain builder to screw up
accidentally.

BTW: On the subject of safety, changelog watchers will have
noticed significant changes to Xen's 'writable pagetables'
implementation. We weren't intending to make changes like this so
late in the 2,0 release cycle, but it came to our attention that
the Opteron CPU's TLB has a PGD entry cache that isn't coherent
with memory[*]. This meant that it would have potentially been
possible for a malicious or compromised guest OS to contrive a
situation where it got to access pages that didn't belong to it.

We've now checked in an alternative implementation which should
be safe on both Intel and AMD.

Ian

[*] The x86 architecture is woefully underspecified in this
respect. Intel CPUs have a PGD entry cache, but current
implementations have a snooping mechanism that meant that our
previous scheme worked fine. 


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Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

On Thu, 9 Sep 2004, Ian Pratt wrote:

>
> Kip,
>
> Out of interest, why have you needed to give FreeBSD its own
> domain builder rather than use the 'generic ELF' one that Linux
> and NetBSD share? (Plan9 has gone with its own builder as it uses
> an a.out image format).
>

At this point I don't really need it any more, but I wrote it before
there was a generic one. I've been spending what time I have flushing
out the remaining bugs in XenoFreeBSD instead of changing a working init
path. I'll of course need to change the init path at some point so that
FreeBSD can run as DOM0.


			-Kip


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Never mind Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

I just burned an extra page so I'm not aliasing the page table - so now
it comes up.


					-Kip



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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

> I just burned an extra page so I'm not aliasing the page table - so now
> it comes up.
> 
> 
> 					-Kip
> 

Excellent! I'd encourage you to continue to avoid the aliasing, as it
may lead to performance degradation in the future. Once you're up can
you kill the low mappings and free the extra page?

 -- Keir


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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

I don't know off hand where it goes away, but this is the comment from
the native locore.s:

/* install a pde for temporary double map of bottom of VA */
        movl    R(KPTphys), %eax
        xorl    %ebx, %ebx
        movl    $NKPT, %ecx
        fillkpt(R(IdlePTD), $PG_RW)

So, odds are it can be g/c'd as soon as pmap_init is run if not earlier.


			-Kip



On Fri, 10 Sep 2004, Keir Fraser wrote:

> > I just burned an extra page so I'm not aliasing the page table - so now
> > it comes up.
> >
> >
> > 					-Kip
> >
>
> Excellent! I'd encourage you to continue to avoid the aliasing, as it
> may lead to performance degradation in the future. Once you're up can
> you kill the low mappings and free the extra page?
>
>  -- Keir
>
>
> -------------------------------------------------------
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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

I'm hitting a bug in the pmap code when switching to multi-user mode. It
looks to me like a bug in Xen, but I don't know for sure yet. I'd like
to try turning on writable pagetables and use the stock i386 pmap.c code
to see how much mileage I get out of that. Is there any documentation on
the writable pagetable interfaces other than wading through the
changesets?


Thanks.

				-Kip



On Fri, 10 Sep 2004, Keir Fraser wrote:

> > I just burned an extra page so I'm not aliasing the page table - so now
> > it comes up.
> >
> >
> > 					-Kip
> >
>
> Excellent! I'd encourage you to continue to avoid the aliasing, as it
> may lead to performance degradation in the future. Once you're up can
> you kill the low mappings and free the extra page?
>
>  -- Keir
>
>
> -------------------------------------------------------
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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

You could look at the Linux 2.6 sparse tree and look for where
CONFIG_WRITABLE_PAGETABLE is used. That'd tell you how it differs from
the old-style interface.

Basically, when building the domain you use DOM0_VMASSIST to specify
that the domain wishes to use writable page tables. Then, when you
want to modify a pte, just write directly to it. And... that's it!

Note that we don't support direct writing to pde's (yet), only to leaf
entries in the multi-level page table.

 -- Keir

> I'm hitting a bug in the pmap code when switching to multi-user mode. It
> looks to me like a bug in Xen, but I don't know for sure yet. I'd like
> to try turning on writable pagetables and use the stock i386 pmap.c code
> to see how much mileage I get out of that. Is there any documentation on
> the writable pagetable interfaces other than wading through the
> changesets?
> 
> 
> Thanks.
> 
> 				-Kip
> 
> 
> 
> On Fri, 10 Sep 2004, Keir Fraser wrote:
> 
> > > I just burned an extra page so I'm not aliasing the page table - so now
> > > it comes up.
> > >
> > >
> > > 					-Kip
> > >
> >
> > Excellent! I'd encourage you to continue to avoid the aliasing, as it
> > may lead to performance degradation in the future. Once you're up can
> > you kill the low mappings and free the extra page?
> >
> >  -- Keir
> >
> >
> > -------------------------------------------------------
> > This SF.Net email is sponsored by: YOU BE THE JUDGE. Be one of 170
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> > _______________________________________________
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> > https://lists.sourceforge.net/lists/listinfo/xen-devel
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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

>
> Note that we don't support direct writing to pde's (yet), only to leaf
> entries in the multi-level page table.

Ahh - then it wouldn't help with this particular problem. I'm getting
an error when I unpin a page as an L2 table and then immediately re-pin
it as an L1.


				-Kip


>
>  -- Keir
>
> > I'm hitting a bug in the pmap code when switching to multi-user mode. It
> > looks to me like a bug in Xen, but I don't know for sure yet. I'd like
> > to try turning on writable pagetables and use the stock i386 pmap.c code
> > to see how much mileage I get out of that. Is there any documentation on
> > the writable pagetable interfaces other than wading through the
> > changesets?
> >
> >
> > Thanks.
> >
> > 				-Kip
> >
> >
> >
> > On Fri, 10 Sep 2004, Keir Fraser wrote:
> >
> > > > I just burned an extra page so I'm not aliasing the page table - so now
> > > > it comes up.
> > > >
> > > >
> > > > 					-Kip
> > > >
> > >
> > > Excellent! I'd encourage you to continue to avoid the aliasing, as it
> > > may lead to performance degradation in the future. Once you're up can
> > > you kill the low mappings and free the extra page?
> > >
> > >  -- Keir
> > >
> > >
> > > -------------------------------------------------------
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> > > https://lists.sourceforge.net/lists/listinfo/xen-devel
> > >
>
>


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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

> >
> > Note that we don't support direct writing to pde's (yet), only to leaf
> > entries in the multi-level page table.
> 
> Ahh - then it wouldn't help with this particular problem. I'm getting
> an error when I unpin a page as an L2 table and then immediately re-pin
> it as an L1.

Please post us the debug output from Xen when this occurs. Might you
still be running on the L2? Whatever -- we can probably narrow it down
with the debug tracing.

 -- Keir


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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Kip Macy]

Zeroing the page in between improves the situation substantially.
Although I'm not sure if it is fixed.


pdb seems broken, to use pdb the symbols for the pdb_ctx variable must
be present, but they aren't:


my options:

verbose     ?= y
debug       ?= y
debugger    ?= y
perfc       ?= n
trace       ?= n

(gdb) ptype pdb_ctx
type = <data variable, no debug info>

gcc -nostdinc -fno-builtin -fno-common -fno-strict-aliasing -O3
-iwithprefix include -Wall -Werror -fomit-frame-pointer -pipe
-I/t/niners/users/xen/xeno-unstable.bk.work.1.1303/xen/include
-Wno-pointer-arith -Wredundant-decls -msoft-float -m32 -march=i686
-DVERBOSE -DXEN_DEBUGGER -c pdb-stub.c -o pdb-stub.o

-- If you stick a -g in there it works a little better:
(gdb) p pdb_ctx
$1 = {
  valid = 0x0,
  domain = 0x0,
  process = 0xfc53bd1a,
  system_call = 0x0,
  ptbr = 0x0
}
(gdb)
but it still won't give me a backtrace like it used to:
(XEN) pdb: [m12,8]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [m12,8]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [m12,1]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [m12,1]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [m12,1]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [m12,1]
(XEN) pdb: L2 error (0x12)
(XEN) pdb: [mc01ab330,1]
(XEN) pdb: L2 error (0xc01ab330)
(XEN) pdb: [mc01ab330,1]
(XEN) pdb: L2 error (0xc01ab330)



On Fri, 10 Sep 2004, Keir Fraser wrote:

> > >
> > > Note that we don't support direct writing to pde's (yet), only to leaf
> > > entries in the multi-level page table.
> >
> > Ahh - then it wouldn't help with this particular problem. I'm getting
> > an error when I unpin a page as an L2 table and then immediately re-pin
> > it as an L1.
>
> Please post us the debug output from Xen when this occurs. Might you
> still be running on the L2? Whatever -- we can probably narrow it down
> with the debug tracing.
>
>  -- Keir
>
>
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Re: Never mind Re: Re: Xen reboots when trying to start new domain

[Keir Fraser]

> When do the changes to the ptes take effect? How does Xen enforce 
> security in this case? My guess would be to detach the leaf table from 
> the page directory, and reattach and check it on demand at first fault. 
> Is this correct? Does Xen keep shadow copies of all pgds then, or only 
> the currently active one? Sounds clever.

You just described version 1 of writable pagetables. In v2, when the
guest tries to write his pagetable we instead give him write access to
a copy of that table. Then, next time he TLB flushes, or the guest
faults on the VA area that th eupdated p.t. maps, we validate any
modifications and copy them back into the real p.t. This means there
is no need to unlink the real p.t. at any point.

 -- Keir


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