On Tue, 2012-08-14 at 15:48 +0200, Jan Kiszka wrote:
> Hi Alex,
>
> you once wrote this comment in device-assignment.c, msix_mmio_write:
>
> if (!msix_masked(&orig) && msix_masked(entry)) {
> /*
> * Vector masked, disable it
> *
> * XXX It's not clear if we can or should actually attempt
> * to mask or disable the interrupt. KVM doesn't have
> * support for pending bits and kvm_assign_set_msix_entry
> * doesn't modify the device hardware mask. Interrupts
> * while masked are simply not injected to the guest, so
> * are lost. Can we get away with always injecting an
> * interrupt on unmask?
> */
>
> I'm wondering what made you think that we won't inject if the vector is
> masked like this (ie. in the shadow MSI-X table). Can you recall the
> details?
>
> I'm trying to refactor this code to make the KVM interface a bit more
> encapsulating the kernel interface details, not fixing anything. Still,
> I would also like to avoid introducing regressions.
Yeah, I didn't leave a very good comment there. I'm sure it made more
sense to me at the time. I think I was trying to say that not only do
we not have a way to mask the physical hardware, but if we did, we don't
have a way to retrieve the pending bits, so any pending interrupts while
masked would be lost. We might be able to deal with that by posting a
spurious interrupt on unmask, but for now we do nothing as masking is
usually done just to update the vector. Thanks,
Alex
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