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

[Marcelo Tosatti <mtosatti@redhat.com>]

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.