Re: [Qemu-devel] Windows balloon driver PFN issue

[Peter Xu]

On Wed, Jan 31, 2018 at 04:03:12PM +0200, Michael S. Tsirkin wrote:
> On Wed, Jan 31, 2018 at 05:28:35PM +0800, Peter Xu wrote:
> > Hi, Michael and the list,
> > 
> > I observed this on windows 8 enterprise guests, when doing memory 
> > ballooning:
> > 
> > address@hidden:virtio_balloon_to_target balloon target: 0x80000000 
> > num_pages: 524288
> > address@hidden:virtio_balloon_get_config num_pages: 524288 actual: 0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x174604000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460a000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460b000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460c000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460d000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460e000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 
> > 0x17460f000
> > address@hidden:virtio_balloon_handle_output section name: pc.ram gpa: 0x0
> > ...
> > 
> > I think it's very possible that these zero addresses (please let me
> > know what the first 4K page is used for if anyone knows, since IIUC
> > that's what we throw away now) are half of the 64bit PFN.  Or say, not
> > sure whether this means a windows guest driver bug that is using
> > 64bits for PFN rather than 32bits (and I suppose the protocol is using
> > 32bit for PFNs).
> > 
> > Michael, do you know what to do with this?
> > 
> > Thanks,
> 
> PFN is GPA>>12.  Do you have more than 1<<44 bytes of memory in this VM then?

No.  But isn't it still not good to drop the page at offset zero (and
drop it NNN times)?  And I'm not sure what will happen if guest has
1<<44 bytes; then we'll possibly drop very random addresses since a
real address will be splitted?

Thanks,

-- 
Peter Xu