On 24.06.14 11:47, Paul Mackerras wrote:
On Mon, Jun 23, 2014 at 06:47:51PM +0200, Alexander Graf wrote:
On 17.06.14 13:39, Eric Auger wrote:
Hello,
I have a question related to KVM_IRQFD and KVM_SET_GSI_ROUTING ioctl
relationship.
When reading the KVM API documentation I do not understand there is any
dependency between KVM_IRQFD and KVM_SET_GSI_ROUTING. According to the
text it seems only the gsi field is used and interpreted as the irqchip pin.
However irqchip.c kvm_set_irq code relies on an existing and not dummy
routing table.
My question is: does anyone agree on the fact the user-side must set a
consistent routing table using KVM_SET_GSI_ROUTING before using
KVM_IRQFD? The other alternative would have been to build a default
identity GSI routing table in the kernel (gsi = irqchip.pin).
I untangled irqfd support from the x86 ioapic emulation a while back. When I
looked at it, I didn't see any easy way to split it out from the routing
too, so I kept that dependency in.
If you look at the code, you will see that the irq routing entry is used as
token for an irqfd. So every irqfd only knows its routing table entry,
nothing else.
As far as I can see, the routing table entry is used for only two
things: to tell whether the interrupt is an MSI or LSI, and to pass to
kvm_set_msi.
One way to tackle the problem would be to abstract out the routing
table lookup into a function in irqchip.c, rather than having it
open-coded in irqfd_update. Then, if you don't want to have the
You could also create it along with the irqfd state struct. So instead of
kzalloc(sizeof(*irqfd), GFP_KERNEL);
we could do
kzalloc(sizeof(*irqfd) + sizeof(struct kvm_kernel_irq_routing_entry),
GFP_KERNEL);
and point the routing entry to the inline irqfd one. We'd lose the
ability to change any routings with that construct, but I think that's
ok for irq controllers that are not configurable.
Alternatively, we could also have a single routing entry that is a
wildcard match, ranging from say LSI [x...y]. The irqfd structure would
then need to carry a local payload to define an offset inside that
wildcard routing entry.
Alex
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