Re: [PATCH v4 0/6] Nonatomic interrupt injection

Marcelo Tosatti
2010-09-17T19:13:18Z

On Thu, Sep 16, 2010 at 03:35:19PM +0200, Avi Kivity wrote:
> On 08/30/2010 02:36 PM, Avi Kivity wrote:
> >This patchset changes interrupt injection to be done from normal process
> >context instead of interrupts disabled context. This is useful for real
> >mode interrupt injection on Intel without the current hacks (injecting as
> >a software interrupt of a vm86 task), reducing latencies, and later, for
> >allowing nested virtualization code to use kvm_read_guest()/kvm_write_guest()
> >instead of kmap() to access the guest vmcb/vmcs.
> >
> >Seems to survive a hack that cancels every 16th entry, after injection has
> >already taken place.
> >
> >With the PIC reset fix posted earlier, this passes autotest on both AMD and
> >Intel, with in-kernel irqchip. I'll run -no-kvm-irqchip tests shortly.
> >
> >Please review carefully, esp. the first patch. Any missing kvm_make_request()
> >there may result in a hung guest.
> >
>
> This is now merged, with the change pointed out by Marcelo. Windows
> XP x64 fails installation without
>
> (vmx.c handle_cr())
> case 8: {
> u8 cr8_prev = kvm_get_cr8(vcpu);
> u8 cr8 = kvm_register_read(vcpu, reg);
> kvm_set_cr8(vcpu, cr8);
> skip_emulated_instruction(vcpu);
> if (irqchip_in_kernel(vcpu->kvm))
> return 1;
> - if (cr8_prev <= cr8)
> - return 1;
> vcpu->run->exit_reason = KVM_EXIT_SET_TPR;
> return 0;
> }
>
> Which doesn't make any sense (anyone?). The failure is present even
> without the patchset, and is fixed by the same hack, so a regression
> was not introduced.

If userspace does not have an uptodate TPR value, it can signal an
interrupt that is now blocked? Say:

- cr8 write 0
- cr8 write 5
- no exit to userspace
- userspace signals interrupt with priority
4 because it knows about tpr == 0.