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

[Anthony Liguori]

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<address@hidden>   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