On 08/02/2017 08:58, Peter Xu wrote:
> This idea was invoked when I was trying to solve an emulated VT-d issue
> when guest kernel setup incorrect IRTE. When that happens, instead of
> raising error immediately, what we should do is to keep the error, and
> inject this error to vIOMMU when the specific interrupt is triggered.
>
> However this is very hard to be achieved since for now vIOMMU is working
> in userspace, while currently there is no simple way that kernel irq can
> talk to a userspace program.
>
> With this patch, we can easily provide such a way that when guest fault
> irq is triggered, kernel can notify user program by signaling the
> corresponding eventfd handle
I think I understand the scenario, but I don't understand why it needs
kernel intervention. Why couldn't this be handled entirely in
userspace, without ever setting up a GSI route or irqfd in KVM? In
other words, you're doing
write(irqfd) read(irq fault eventfd)
| ^
v |
KVM -------> KVM_GSI_ROUTING_EVENTFD
but why is this needed as opposed to just
write(irqfd) ------> read(irq fault eventfd)
?
Thanks,
Paolo
