[Spice-devel] [xf86 qxl driver PATCH 5/5] qxl_driver: monitors_config: adjust to memory-remap

[Uri Lublin]

On 01/21/2013 04:16 PM, Yonit Halperin wrote:
> On 01/17/2013 09:26 AM, Uri Lublin wrote:
>> Resolves: rhbz#883578
>>
>> Call qxl_allocate_monitors_config upon memory-remap such
>> that qxl->monitors_config points to the start of
>> monitors_config segment in qxl RAM memory.
>>
>> Currently after memory remap, it's possible that monitors_config
>> memory and video-memory (or graphics) overlap, which means
>> that one may overwrite another.
>> Specifically in the bug above, monitors_config value are being
>> overwritten by video pages, and on the destination bad values
>> are read which cause problems on the server and client.
>>
> Can you please explain the path that leads to this overwriting?
> I see that in qxl_map_memory qxl_allocate_monitors_config is already 
> called.
>> It may be a good idea to add some protection on the server side,
>> e.g. calcluate checksum, compare values against modes, or limit
>> ->count and ->max_allowed and ignore bad monitors_config values
>>
>> Also do not memset-0 monitors-config upon allocation (remapping)
>> to not overwrite likely good configuration (in case it is
>> being read by the host, e.g. upon migration).
> I'm not sure that the code in qemu-qxl should even re-read the 
> monitors configuration during pre-save because it was already updated 
> on the UPDATE_MONITORS_CONFIG io call.

Hi Yonit,

The source host does not re-reads the monitors configuration during 
pre-save.
The destination host reads it during post-reload.

The monitors_config area is migrated together with all the VM memory.
And the address to the monitors configuration is transferred as state.

Thanks,
     Uri.