From mboxrd@z Thu Jan  1 00:00:00 1970
From: Kip Macy <kip.macy@gmail.com>
Subject: Re: writable page tables appear to be causing xen to lock
	up
Date: Tue, 19 Apr 2005 10:28:20 -0700
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To: Ian Pratt <m+Ian.Pratt@cl.cam.ac.uk>
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My guess from this is FreeBSD is DOSing xen by endlessly triggering
failsafe_callback. Although this is *extremely* likely to be my fault,
it raises an interesting point about the need for heavily reducing the
scheduling priority of misbehaved guests.


0xfc550862 <__copy_from_user_ll+53>:    repz movsb %ds:(%esi),%es:(%edi)=20
0xfc552df4 <failsafe_callback+233>:     push   %ecx=20
0xfc54df1e <error_code+94>:     add    $0x4,%esp=20
0xfc550862 <__copy_from_user_ll+53>:    repz movsb %ds:(%esi),%es:(%edi)
0xfc5508f4 <copy_from_user+60>: mov    %eax,%ebx
0xfc54da4f <x86_emulate_read_std+40>:   test   %eax,%eax
0xfc54abfc <x86_emulate_memop+176>:     mov    %eax,0xffffffd4(%ebp)
0xfc54dae5 <memcpy+31>: leave
0xfc54cdca <x86_emulate_memop+8830>:    cmpl $0x1,0xffffffd4(%ebp)
0xfc52ba0f <alloc_l1_table+211>:        movl   $0x1,0xffffffec(%ebp)
0xfc52c3a0 <alloc_page_type+72>:        mov    %eax,0xfffffffc(%ebp)
0xfc52cab6 <get_page_type+860>: movl   $0x1,0xffffffd8(%ebp)
0xfc52e6a6 <do_mmu_update+2826>:        mov    0xffffffd8(%ebp),%eax
0xfc5304c1 <ptwr_do_page_fault+1070>:   test   %eax,%eax
0xfc5426b3 <debugger_trap_entry+11>:    mov    %eax,0xfffffffc(%ebp)
0xfc540100 <do_page_fault+300>: test   %eax,%eax
0xfc53ff60 <propagate_page_fault+18>:   mov    %eax,0xfffffff4(%ebp)
0xfc540330 <do_page_fault+860>: movl   $0x0,0xffffffe0(%ebp)
0xfc54df1e <error_code+94>:     add    $0x4,%esp
0xfc54dda3 <FLT14>:     mov    %eax,%gs:(%esi)
0xfc54de75 <process_guest_exception_and_events+21>:     jmp  =20
0xfc54dcd7 <test_all_events>

On 4/18/05, Kip Macy <kip.macy@gmail.com> wrote:
> > You'll have to give us a bit more to go on. I presume this is in
> > unstable?
>=20
> Yes this is as of your last pushed checkin from 72hrs ago. LOL. If I
> had more I'd give it to you. I've just disabled writable pagetables in
> FreeBSD for the moment.
>=20
>=20
> > It's probably worth adding a show_stack and a show_guest_stack to see
> > how you're getting there.
>=20
> I'll stick that in and let you know.
>=20
>  -Kip
>