Re: [Qemu-devel] [PATCH] ppc64: fix compressed dump with pseries kernel

[Thomas Huth]

On 05.08.2016 09:49, David Gibson wrote:
> On Thu, Aug 04, 2016 at 10:41:16AM +0200, Laurent Vivier wrote:
> 1;4402;0c> 
>>
>> On 04/08/2016 04:38, David Gibson wrote:
>>> On Wed, Aug 03, 2016 at 09:55:07PM +0200, Laurent Vivier wrote:
>>>> If we don't provide the page size in target-ppc:cpu_get_dump_info(),
>>>> the default one (TARGET_PAGE_SIZE, 4KB) is used to create
>>>> the compressed dump. It works fine with Macintosh, but not with
>>>> pseries as the kernel default page size is 64KB.
>>>>
>>>> Without this patch, if we generate a compressed dump in the QEMU monitor:
>>>>
>>>>     (qemu) dump-guest-memory -z qemu.dump
>>>>
>>>> This dump cannot be read by crash:
>>>>
>>>>     # crash vmlinux qemu.dump
>>>>     ...
>>>>     WARNING: cannot translate vmemmap kernel virtual addresses:
>>>>              commands requiring page structure contents will fail
>>>>     ...
>>>>
>>>> Signed-off-by: Laurent Vivier <address@hidden>
>>>> ---
>>>>  target-ppc/arch_dump.c | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>
>>> Urgh.. so, really the page size used by the guest kernel is a
>>> guest-side detail, and it's certainly possible to build a 4kiB page
>>> guest kernel, although 64kiB is the norm.
>>
>> virtio-balloon doesn't work with 4K kernel.
> 
> It doesn't?  Balloon has rather a lot of flaws, but I didn't think
> that was one of them.

It currently doesn't work when the guest uses 4k page size but the host
uses 64k page size. Do you remember this bug ticket:
https://bugzilla.redhat.com/show_bug.cgi?id=1323988 ?
... we just decided not to spent time on this because no distro is using
4k page size for the pseries platform anymore, and the virtio-balloon
code is currently under major reconstruction anyway.

 Thomas

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