[Xen-devel] Re: [Xen-users] rebased openSUSE Xen dom0 Patches

["Simon Graham" <simon.graham@xxxxxxxxxxxxxxxxxxx>]

On Tue, Apr 06, 2010 at 02:37:35PM +0100, Andrew Lyon wrote:
> I've uploaded updated 2.6.31 and 2.6.32 rebased openSUSE Xen dom0
> patches and ebuilds to
> http://code.google.com/p/gentoo-xen-kernel/downloads/list
> 
> Notable change is that both include the online resize feature recently
> posted to xen-devel.
>

We're currently testing these patches with the Ubuntu 10.4 kernel and Xen 3.4.2 
and have encountered some problems in the Xen mm code shortly after Dom0 starts 
to run.

The typical failure is that Dom0 is trying to write to a page table (a L4 PT in 
the example below) but finds the page it is writing to is a PGT_writable_page

...
(XEN) mm.c:2410:d0 Bad type (saw e800000000000001 != exp 8000000000000000) for 
mfn 0x114702 (pfn 0x702)
(XEN) mm.c:2802:d0 Error while pinning mfn 114702
[   18.549043] HYPERVISOR_mmuext_op failed:  pgd ffff880000703000 cmd0=3 
mfn0=114702 cmd1=3 mfn1=114703 err=-22
[   18.549689] ------------[ cut here ]------------
[   18.549975] kernel BUG at 
/sandbox/orc-tree-10.4/orc-kernel/linux-2.6.32/arch/x86/mm/hypervisor.c:680!
[   18.550542] invalid opcode: 0000 [#1] SMP 

Another common failure is shown below.  Dom0 expects a page to 
be PGT_l1_page_table but instead finds the page's type is PGT_writable_page:

(XEN) mm.c:2410:d0 Bad type (saw e800000000000001 != exp 2000000000000000) for 
mfn 0x114711 (pfn 0x711)
(XEN) mm.c:2413:d0 Writable page alloc'd from ptwr_do_page_fault:4481
(XEN) mm.c:821:d0 Attempt to create linear p.t. with write perms
[   21.159495] HYPERVISOR_multicall_check failed on call 1 rc 4294967274
[   21.159498] HYPERVISOR_multicall_check failed page=ffff8800020bbc00 pfn=1808
[   21.159503] ------------[ cut here ]------------
[   21.159505] kernel BUG at 
/sandbox/orc-tree-10.4/orc-kernel/linux-2.6.32/arch/x86/mm/hypervisor.c:480!

It is not clear whether Dom0 is erroneously using pages that are and truly 
should be writable, or whether somehow pages have erroneously become writable; 
if anyone can suggest likely places to look for problems that would be awesome!

Simon


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