Re: [Qemu-devel] [PATCH V8 1/4] mem: add share parameter to memory-backend-ram

[Eduardo Habkost]

On Thu, Feb 01, 2018 at 06:48:54PM +0200, Michael S. Tsirkin wrote:
> On Thu, Feb 01, 2018 at 02:31:32PM -0200, Eduardo Habkost wrote:
> > On Thu, Feb 01, 2018 at 04:24:30PM +0200, Michael S. Tsirkin wrote:
> > [...]
> > > The full fix would be to allow QEMU to map a list of
> > > pages to a guest supplied IOVA.
> > 
> > Thanks, that's what I expected.
> > 
> > While this is not possible, the only requests I have for this
> > patch is that we clearly document:
> > * What's the only purpose of share=on on a host-memory-backend
> >   object (due to pvrdma limitations).
> > * The potential undesirable side-effects of setting share=on.
> > * On the commit message and other comments, clearly distinguish
> >   HVAs in the QEMU address-space from IOVAs, to avoid confusion.
> 
> Looking forward, when we do support it, how will management find out
> it no longer needs to pass the share parameter?
> 
> Further, if the side effects of the share parameter go away,
> how will it know these no longer hold?

A query-host-capabilities or similar QMP command seems necessary
for that.  It would be useful for other stuff like MAP_SYNC.

-- 
Eduardo