Re: [PATCH] pci-assign: Do not expose MSI/MSI-X if the kernel does not support it

[Alex Williamson <alex.williamson@redhat.com>]

On Tue, 2011-08-02 at 19:32 +0200, Jan Kiszka wrote:
> On 2011-08-02 19:02, Alex Williamson wrote:
> > On Tue, 2011-08-02 at 14:27 +0200, Jan Kiszka wrote:
> >> Add checks for KVM_CAP_ASSIGN_DEV_IRQ (MSI) and KVM_CAP_DEVICE_MSIX, do
> >> not set up MSI/MSI-X if the required kernel features are missing.
> >>
> >> Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
> >> ---
> >>  hw/device-assignment.c |    6 ++++--
> >>  1 files changed, 4 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/hw/device-assignment.c b/hw/device-assignment.c
> >> index 4cc7b1a..7e965cb 100644
> >> --- a/hw/device-assignment.c
> >> +++ b/hw/device-assignment.c
> >> @@ -1201,7 +1201,8 @@ static int assigned_device_pci_cap_init(PCIDevice *pci_dev)
> >>  
> >>      /* Expose MSI capability
> >>       * MSI capability is the 1st capability in capability config */
> >> -    if ((pos = pci_find_cap_offset(pci_dev, PCI_CAP_ID_MSI, 0))) {
> >> +    pos = pci_find_cap_offset(pci_dev, PCI_CAP_ID_MSI, 0);
> >> +    if (pos != 0 && kvm_check_extension(kvm_state, KVM_CAP_ASSIGN_DEV_IRQ)) {
> > 
> > Is it even useful to have a device assigned w/o KVM_CAP_ASSIGN_DEV_IRQ?
> 
> If that feature is lacking, we fall back to the old KVM_ASSIGN_IRQ
> interface. I guess that used to work, but I bet no one tested it
> recently. However, the code is there, also in the kvm core.

Ah right.  Not sure how much I trust that, but seems obviously correct
to not expose capabilities we can't support.

Acked-by: Alex Williamson <alex.williamson@redhat.com>