Re: [Xen-devel] [xen-unstable test] 13394: regressions - FAIL

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

xen.org writes ("[xen-unstable test] 13394: regressions - FAIL"):
> Tests which did not succeed and are blocking,
> including tests which could not be run:
>  test-amd64-amd64-xl-qemuu-winxpsp3  9 guest-localmigrate fail REGR. vs. 13379

The logs show this:

  libxl: error: libxl_dom.c:632:switch_logdirty_timeout: logdirty switch: wait 
for device model timed out

And in xenstore:

  /local/domain/0/device-model/5/logdirty/cmd = "enable"   (n0)

And in the source code:

  $ grep -R logdirty qemu-upstream-unstable.git/*
  $

So the upstream qemu does not participate properly in the migration
protocol.  And anyway this protocol seems to involve xenstore and I
would have expected it to do something with QMP.  But there is no code
in libxl to do this (and never has been) and no code in upstream qemu
to do it either.

That means we'll get memory corruption in migrated guests with the new
qemu: any time qemu writes to guest memory, it needs to trigger a
logdirty update so that the write is properly transferred to the
migration target domain.

With the old libxl we didn't notice this apart from random failures.
With my new migration code, particularly
   25542:1883e5c71a87
   libxl: wait for qemu to acknowledge logdirty command
this turns into a hard failure.

I will add this as an allowable test failure pending a proper fix.

Ian.

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