Re: [Qemu-devel] rfc: vhost user enhancements for vm2vm communication

[Nakajima, Jun]

On Tue, Sep 1, 2015 at 9:28 AM, Jan Kiszka <address@hidden> wrote:
> On 2015-09-01 18:02, Michael S. Tsirkin wrote:
...
>> You don't need to be able to map all guest memory if you know
>> guest won't try to allow device access to all of it.
>> It's a question of how good is the bus address allocator.
>
> But those BARs need to allocate a guest-physical address range as large
> as the other guest's RAM is, possibly even larger if that RAM is not
> contiguous, and you can't put other resources into potential holes
> because VM2 does not know where those holes will be.
>

I think you can allocate such guest-physical address ranges
efficiently if each BAR sets the base of each memory region reported
by VHOST_SET_MEM_TABLE, for example.  The issue is that we would need
to 8 (VHOST_MEMORY_MAX_NREGIONS) of them vs. 6 (defined by PCI-SIG).

-- 
Jun
Intel Open Source Technology Center