Re: [PATCH v5 4/4] KVM: x86: Add support for local interrupt requests from userspace

[Steve Rutherford <srutherford@google.com>]

On Wed, Jul 29, 2015 at 12:05:37AM +0200, Paolo Bonzini wrote:
> Ok, I understand it now.  However, you're still not causing an exit 
> when LVT0 changes, are you?  post_kvm_run_save is not run until the
> next exit to userspace, which could be a long time later.

Yes! This is definitely right. This may wait as long as an entire entry/exit
before actually exiting to userspace. Moving into dm_request_for_irq_injection
is definitely the way to go.
> 
> So, I think that you do not need KVM_REQ_PIC_UNMASK_EXIT.  Instead,
> you can modify dm_request_for_irq_injection to handle the split-irqchip
> case, like this:
> 
> 	if (!vcpu->run->request_interrupt_window || pic_in_kernel(vcpu->kvm))
> 		return false;
> 
> 	if (kvm_cpu_has_interrupt(vcpu))
> 		return false;
> 
>         return (irqchip_split(vcpu->kvm)
>                 ? kvm_apic_accept_pic_intr(vcpu)
> 		: kvm_arch_interrupt_allowed(vcpu));
> 
> This will cause KVM_RUN to return -EINTR, which QEMU happens to handle
> the same way as KVM_EXIT_IRQ_WINDOW_OPEN.
I definitely prefer the explit exit reason.
It's also a bit easier to make work with our VMM ;)

> Feel free to post v6 of this patch only.  Everything else is mostly
> okay; there are some leftovers here and there (lapic_in_kernel,
> GET_VECTOR_FROM_USERSPACE) but I can fix that.
I'll give it another once over to remove the dead code. Sorry about
leaving that junk in.

> How is the integration with QEMU going?  With this latest iteration
> it should be relatively easy.
A new team member is sinking his teeth into it, as an starter project. 
He'll likely have a prototype of it working soon. 

Steve
> 
> Paolo