Re: [Xen-devel] error in xen/arch/x86/mm.c:get_page during migration

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.02.13 at 18:31, Olaf Hering <olaf@xxxxxxxxx> wrote:
> It did not happen with xl.

But the same guest and Dom0 kernel, and the same hypervisor?

> Here is the output while doing xm migrate:
> 
> (XEN) HVM2 restore: VMCE_VCPU 0
> (XEN) HVM2 restore: VMCE_VCPU 1
> (XEN) HVM2 restore: TSC_ADJUST 0
> (XEN) HVM2 restore: TSC_ADJUST 1
> (XEN) mm.c:1983:d0 Error pfn 4112c5: rd=ffff83036ffef000, 
> od=0000000000000000, caf=180000000000000, taf=7400000000000001

Didn't even notice yesterday that this is apparently after restore
has already started. Which makes me curious whether the domain
that is being referenced with rd= is the old or the new one (would
require printing the domain ID; honestly I never understood what
use printing of the domain pointer is).

I'm also confused by the domain pointer always being the same;
I would expect it to at least toggle between two values, but
probably even be different between every instance of the guest.
But you're not having a stubdom configured for the guest either,
according to the config you sent earlier...

> (XEN) Xen call trace:
> (XEN)    [<ffff82c4c0170fb2>] get_page+0xfb/0x151
> (XEN)    [<ffff82c4c01e1d87>] get_page_from_gfn_p2m+0x17e/0x284
> (XEN)    [<ffff82c4c01098ae>] __get_paged_frame+0x5d/0x170
> (XEN)    [<ffff82c4c0109e55>] __acquire_grant_for_copy+0x494/0x6ae
> (XEN)    [<ffff82c4c010bef0>] gnttab_copy+0x53b/0x843
> (XEN)    [<ffff82c4c010e3b8>] do_grant_table_op+0x11c5/0x1b82
> (XEN)    [<ffff82c4c011502f>] do_multicall+0x227/0x444
> (XEN)    [<ffff82c4c0227f0b>] syscall_enter+0xeb/0x145

The only user of grant copies is netback, and hence I would suppose
that the failed transmit (in whichever direction) is simply being retried,
thus preventing the error from becoming user visible.

Jan


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