Re: Problem about dump-core

[Ian Campbell <ian.campbell@citrix.com>]

On Tue, 2014-09-16 at 15:23 +0800, Wen Congyang wrote:
> On 09/16/2014 10:35 AM, Wen Congyang wrote:
> > Hi, everyone:
> > 
> > The command 'xl dump-core' will fail after migration. The guest is HVM guest(without pv driver).
> > I use the newest staging branch to test. Both source and dest dom0 use the same kernel.
> 
> The kernel version is 3.2, and it only supports IOCTL_PRIVCMD_MMAPBATCH.
> 
> After more investigation, the reason is that the mfn is ~0UL, and xc_map_foreign_range()
> doesn't return NULL on dest host.
> 
> This patch can fix this problem:
> 
> From: Wen Congyang <wency@cn.fujitsu.com>
> Date: Tue, 16 Sep 2014 14:56:03 +0800
> Subject: [PATCH] check if mfn is valid before checking if PRIVCMD_MMAPBATCH_MFN_ERROR is set
> 
> If mfn is invalid, ioctl(fd, IOCTL_PRIVCMD_MMAPBATCH, ..) also returns 0,
> and we set mfn to mfn | PRIVCMD_MMAPBATCH_MFN_ERROR. But if mfn is ~0UL,
> pfn[i] ^ arr[i] returns 0, and we cannot find this error. So we should
> check if mfn is valid first before testing pfn[i] ^ arr[i].

I don't think we can reliably distinguish between a large MFN and an
error with this approach, can we?

I suspect it would be better to perform a check before making the
hypercall that the 4 (?) error bits are not set in the input.

Ian.