PCI/kernel msi code vs GIC ITS driver conflict?
From: John Garry
Date: Tue Sep 03 2019 - 10:09:54 EST
Hi Marc, Bjorn, Thomas,
We've come across a conflict with the kernel/pci msi code and GIC ITS
driver on our arm64 system, whereby we can't unbind and re-bind a PCI
device driver under special conditions. I'll explain...
Our PCI device support 32 MSIs. The driver attempts to allocate msi
vectors with min msi=17, max msi = 32, and affd.pre vectors = 16. For
our test we make nr_cpus = 1 (just anything less than 16).
We find that the pci/kernel msi code gives us 17 vectors, but the GIC
ITS code reserves 32 lpi maps in its_irq_domain_alloc(). The problem
then occurs when unbinding the driver in its_irq_domain_free() call,
where we only clear bits for 17 vectors. So if we unbind the driver and
then attempt to bind again, it fails.
Where the fault lies, I can't say. Maybe the kernel msi code should
always give power of 2 vectors - as I understand, the PCI spec mandates
this. Or maybe the GIC ITS driver has a problem in the free path, as
above. Or maybe the PCI driver should not be allowed to request !power
of 2 min/max vectors.
Thanks in advance,