On 2012-08-14 16:05, Alex Williamson wrote:
> 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,
Ok, thanks for the clarification.
As we are at it, do you also recall if this
--- a/hw/device-assignment.c
+++ b/hw/device-assignment.c
@@ -1573,28 +1573,7 @@ static void msix_mmio_write(void *opaque,
target_phys_addr_t addr,
*/
} else if (msix_masked(&orig) && !msix_masked(entry)) {
/* Vector unmasked */
- if (i >= adev->irq_entries_nr || !adev->entry[i].type) {
- /* Previously unassigned vector, start from scratch */
- assigned_dev_update_msix(pdev);
- return;
- } else {
- /* Update an existing, previously masked vector */
- struct kvm_irq_routing_entry orig = adev->entry[i];
- int ret;
-
- adev->entry[i].u.msi.address_lo = entry->addr_lo;
- adev->entry[i].u.msi.address_hi = entry->addr_hi;
- adev->entry[i].u.msi.data = entry->data;
-
- ret = kvm_update_routing_entry(&orig, &adev->entry[i]);
- if (ret) {
- fprintf(stderr,
- "Error updating irq routing entry (%d)\n", ret);
- return;
- }
-
- kvm_irqchip_commit_routes(kvm_state);
- }
+ assigned_dev_update_msix(pdev);
}
}
}
would make a relevant difference for known workloads? I'm trying to get
rid of direct routing table manipulations, but I would also like to
avoid introducing things like kvm_irqchip_update_msi_route unless really
necessary. Or could VFIO make use of that as well?
Jan
PS: Will try to have a look at your main VFIO patch later today.
--
Siemens AG, Corporate Technology, CT RTC ITP SDP-DE
Corporate Competence Center Embedded Linux
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