Re: [Qemu-devel] [PATCH v3 0/7] Let boards state maximum RAM limits in QEMUMachine struct

[Jes Sorensen]

On 03/29/11 16:08, Peter Maydell wrote:
> This primary aim of this patchset is to add a new 'max_ram' field to the
> QEMUMachine structure so that a board model can specify the maximum RAM it
> will accept.  We can then produce a friendly diagnostic message when the
> user tries to start qemu with a '-m' option asking for more RAM than that. 
> (Currently most of the ARM devboard models respond with an obscure guest
> crash when the guest tries to access RAM and finds device registers
> instead.)
> 
> If no maximum size is specified we default to the old behaviour of
> "do not impose any limit".
> 
> The bulk of the patchset is knock-on cleanup as a result, in particular
> allowing QEMUMachine structs to be const and sun4m cleanup.

Hi Peter,

Sorry for not getting to this patch earlier.

I am a little concerned about this approach. It should work for simple
embedded boards, but for larger systems, it really ought to be a mask
rather than a max address. On NUMA systems you are bound to have holes,
and at times you might not even start from address 0. In these cases you
are likely to have device registers mapped in between the memory chunks.

Ideally I think it would be better to have a mask and then introduce a
is_valid_memory() kinda function to check it with.

I fear that by introducing a simple max limit like this, we are going to
hit problems later when we try to improve the NUMA support.

Cheers,
Jes