Re: [Qemu-devel] [PATCH RFC] vga: flag vga ram for notifiers

[Anthony Liguori <anthony@codemonkey.ws>]

On 03/31/2011 04:26 PM, Michael S. Tsirkin wrote:
> On Thu, Mar 31, 2011 at 02:29:50PM -0500, Anthony Liguori wrote:
>> On 03/31/2011 02:18 PM, Peter Maydell wrote:
>>> On 31 March 2011 20:01, Anthony Liguori<anthony@codemonkey.ws>   wrote:
>>>> VGA is just another device.  It happens to be that we treat VGA device
>>>> memory as something that behaves like ram occassionally but that does not
>>>> make it RAM.
>>> So, to ask a dumb question, what does make something RAM?
>> It's a made up concept that we use to make device performance faster.
>>
>> Basically, RAM should include all of the memory that a reasonable
>> device (that we control) would DMA to and has a relatively stable
>> mapping.
>>
>>> My take on RAM is that RAM is just another device; the only
>>> difference is that you want to be able to implement fast
>>> paths that go straight(ish) to target memory; but that's
>>> an optimisation detail, not something that makes RAM
>>> conceptually different from other devices...
>> Right, the trouble is, if you want to treat RAM like any other
>> device, you can't get stable mappings to it which is bad for
>> something like vhost-net.
>>
>> Regards,
>>
>> Anthony Liguori
> Not only that I guess. Removing the VGA memory with the baloon
> will likely also be a bad idea.

It's just the equivalent of a memset(0).  It would be a silly thing for 
a guest to do but not somethign to be concerned about.

Regards,

Anthony Liguori