Re: [PATCH v2] vfio/pci: Verify each MSI vector to avoid invalid MSI vectors

[Jason Gunthorpe]

On Wed, Nov 23, 2022 at 09:42:36AM +0800, chenxiang via wrote:
> From: Xiang Chen <chenxiang66@hisilicon.com>
> 
> Currently the number of MSI vectors comes from register PCI_MSI_FLAGS
> which should be power-of-2 in qemu, in some scenaries it is not the same as
> the number that driver requires in guest, for example, a PCI driver wants
> to allocate 6 MSI vecotrs in guest, but as the limitation, it will allocate
> 8 MSI vectors. So it requires 8 MSI vectors in qemu while the driver in
> guest only wants to allocate 6 MSI vectors.
> 
> When GICv4.1 is enabled, it iterates over all possible MSIs and enable the
> forwarding while the guest has only created some of mappings in the virtual
> ITS, so some calls fail. The exception print is as following:
> vfio-pci 0000:3a:00.1: irq bypass producer (token 000000008f08224d) 
> registration
> fails:66311

With Thomas's series to make MSI more dynamic this could spell future
problems, as future kernels might have different ordering.

It is just architecturally wrong to tie the MSI programming at the PCI
level with the current state of the guest's virtual interrupt
controller.

Physical hardware doesn't do this, virtual emulation shouldn't either.

People are taking too many liberties with trapping the PCI MSI
registers through VFIO. :(

Jason