Re: [Qemu-devel] [RFC 0/3] Draft implementation of HPT resizing (qemu side)

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Mon, Jan 18, 2016 at 04:44:38PM +1100, David Gibson wrote:
> Here is a draft qemu implementation of my proposed PAPR extension for
> allowing runtime resizing of a KVM/ppc64 guest's hash page table.
> That in turn will allow for more flexible memory hotplug.
> 
> This should work with the guest kernel side patches I also posted
> recently [1].
> 
> Still required to make this into a full implementation:
>   * Guest needs to auto-resize HPT on memory hotplug events
> 
>   * qemu needs to allocate HPT size based on current rather than
>     maximum memory if the guest is HPT resize aware
> 
>   * KVM host side implementation
> 
>   * PAPR standardization

So with the current patchset (QEMU and guest kernel changes), I should
be able to change the HTAB size of a PR guest right ? I see the below
failure though:

[root@localhost ~]# cat /sys/kernel/debug/powerpc/pft-size 
24
[root@localhost ~]# echo 26 > /sys/kernel/debug/powerpc/pft-size
[   65.996845] lpar: Attempting to resize HPT to shift 26
[   65.996845] lpar: Attempting to resize HPT to shift 26
[   66.113596] lpar: HPT resize to shift 26 complete (109 ms / 6 ms)
[   66.113596] lpar: HPT resize to shift 26 complete (109 ms / 6 ms)

PR guest just hangs here while I see tons of below messages in
the 1st level guest:

KVM can't copy data from 0x3fff99e91400!
...
Couldn't emulate instruction 0x00000000 (op 0 xop 0)
kvmppc_handle_exit_pr: emulation at 700 failed (00000000)

Regards,
Bharata.