On 1/30/19 6:55 AM, Paul Mackerras wrote:

On Tue, Jan 29, 2019 at 06:44:50PM +0100, Cédric Le Goater wrote:

quoted

On 1/29/19 5:12 AM, Paul Mackerras wrote:

quoted

On Mon, Jan 28, 2019 at 07:26:00PM +0100, Cédric Le Goater wrote:

quoted

Is clearing the PTEs and repopulating the VMA unsafe ? 

Actually, now that I come to think of it, there could be any number of
VMAs (well, up to almost 64k of them), since once you have a file
descriptor you can call mmap on it multiple times.

The more I think about it, the more I think that getting userspace to
manage the mappings with mmap() and munmap() is the right idea if it
can be made to work.

We might be able to mmap() and munmap() regions of ESB pages in the RTAS 
call "ibm,change-msi".  I think that's the right spot for it. 

I was thinking that the ESB pages should be mmapped for device
interrupts at VM startup or when a device is hot-plugged in, and
munmapped when the device is hot-removed.  Maybe the mmap could be
done in conjunction with the KVM_IRQFD call?

What is the reasoning behind doing it in the ibm,change-msi call?

Because when the device is plugged in, it has no interrupts. These are 
allocated on demand only when the driver is loaded in the guest. 

C.