Re: virtio & hypercall interface?

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Rusty Russell wrote:
> On Sat, 2007-09-15 at 01:31 +0300, Dor Laor wrote:
>   
>> Second, regardless of the channel signal notification, there are still 
>> real necessities for userspace hypercall handling:
>> 1. For virtio drivers there is also registration hypercall for passing 
>> the shared memory pfns.
>>     Sure there are other possibilities, but why limit ourselves?
>>     
>
> I really prefer doing this the more "hardware-like" way and having the
> device description say where the pages are.  Surely this is simpler from
> the qemu side, too?
>   

This is mmio style (device provides memory).  DMA style (guest provides
memory, device dmas it) is easier for kvm: we don't need to allocate a
new memory slot, and migration is easier.

Most current hardware place the descriptor ring in guest memory, not the
device, since mmio is slower for the cpu than RAM.



-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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