Re: [PATCH 2/2] hyperv/synic: Allocate as ram_device

[Roman Kagan]

On Thu, Jan 09, 2020 at 02:00:00PM +0100, Vitaly Kuznetsov wrote:
> "Dr. David Alan Gilbert" <address@hidden> writes:
> 
> > And I think vhost-user will fail if you have too many sections - and
> > the 16 sections from synic I think will blow the slots available.
> >
> 
> SynIC is percpu, it will allocate two 4k pages for every vCPU the guest
> has so we're potentially looking at hundreds of such regions.

Indeed.

I think my original idea to implement overlay pages word-for-word to the
HyperV spec was a mistake, as it lead to fragmentation and memslot
waste.

I'll look into reworking it without actually mapping extra pages over
the existing RAM, but achieving overlay semantics by just shoving the
*content* of the "overlaid" memory somewhere.

That said, I haven't yet fully understood how the reported issue came
about, and thus whether the proposed approach would resolve it too.

Thanks,
Roman.