Re: [PATCH 0/4] MSI-X Enabling

Sheng Yang
2008-12-24T03:00:36Z

On Wednesday 24 December 2008 04:19:32 Marcelo Tosatti wrote:
> On Tue, Dec 23, 2008 at 04:12:49PM +0800, Sheng Yang wrote:
> > Hi Avi
> >
> > This patchset would enable MSI-X support.
> >
> > The main change is a new kind of fake device - intercepted MMIO device is
> > added for supporting to intercept one page contained MSI-X entries table.
> >
> > I also consider of doing this intercept in userspace. But I think it's
> > would be more complex to push it in userspace, for we also have to
> > prevent KVM from creating page table for the page.
>
> Unmapping the page in userspace (with munmap) from the PCI MMIO map will
> disallow KVM from creating pagetable for the page.
>
> > And in the future, we would add hook
> > function in the read/write operation to enabling mask bit for each MSI-X
> > entry, may be with pending bits.
>
> Can you explain it in more detail? Can't do it from userspace?
>
> Are there performance considerations to access in this page?
>
> > So I decided to put it in the kernel.
> >
> > Another thing is I am not very confident about modify the position of
> > handling guest memory and MMIO in emulate read/write function. Is it
> > would cause any side affect?
>
> Should not be necessary if done in userspace.

Oops...

After reconsider, I think I have made a design mistake here. MMIO should can
be emulated in userspace...

I would update the patch.

--
regards
Yang, Sheng