On Thu, 24 Mar 2011 10:54:05 +0100, Christian Borntraeger <borntrae...@de.ibm.com> wrote: > Am 24.03.2011 04:05, schrieb Anthony Liguori: > >> ie. lguest and S/390 don't trap writes to config space. > >> > >> Or perhaps they should? But we should be explicit about needing it... > > I don't think we ever operated on the assumption that config space writes > > would trap. > > > > I don't think adding it is the right thing either because you can do byte > > access to the config space which makes atomicity difficult. > > There is the additional problem, that s390 has no MMIO and,therefore, > there is no real HW support for trapping writes to an area. You can > use page faults, or read-only faults on newer systems, but this is > expensive. In addition, page faults only deliver the page frame, but > not the offset within a page.
That's not *really* a problem, since you have control over the config_set operation and could do whatever you wanted. But I wanted to make sure we're all on the same page: you *can't* rely on the host knowing immediately what you write to the config space. If you want that, an actual queued request is necessary... Thanks, Rusty.
