Hi Alex, On 3/17/2023 4:01 PM, Alex Williamson wrote: > On Fri, 17 Mar 2023 15:21:09 -0700 > Reinette Chatre <reinette.chatre@xxxxxxxxx> wrote: > >> Hi Alex, >> >> On 3/17/2023 2:05 PM, Alex Williamson wrote: >>> On Wed, 15 Mar 2023 13:59:28 -0700 >>> Reinette Chatre <reinette.chatre@xxxxxxxxx> wrote: >>> >>>> Dynamic MSI-X is supported. Clear VFIO_IRQ_INFO_NORESIZE >>>> to provide guidance to user space. >>>> >>>> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx> >>>> --- >>>> drivers/vfio/pci/vfio_pci_core.c | 2 +- >>>> include/uapi/linux/vfio.h | 3 +++ >>>> 2 files changed, 4 insertions(+), 1 deletion(-) >>>> >>>> diff --git a/drivers/vfio/pci/vfio_pci_core.c b/drivers/vfio/pci/vfio_pci_core.c >>>> index ae0e161c7fc9..1d071ee212a7 100644 >>>> --- a/drivers/vfio/pci/vfio_pci_core.c >>>> +++ b/drivers/vfio/pci/vfio_pci_core.c >>>> @@ -1111,7 +1111,7 @@ static int vfio_pci_ioctl_get_irq_info(struct vfio_pci_core_device *vdev, >>>> if (info.index == VFIO_PCI_INTX_IRQ_INDEX) >>>> info.flags |= >>>> (VFIO_IRQ_INFO_MASKABLE | VFIO_IRQ_INFO_AUTOMASKED); >>>> - else >>>> + else if (info.index != VFIO_PCI_MSIX_IRQ_INDEX) >>>> info.flags |= VFIO_IRQ_INFO_NORESIZE; >>>> >>> >>> I think we need to check pci_msix_can_alloc_dyn(), right? Thanks, >> >> Can pci_msix_can_alloc_dyn() ever return false? >> >> I cannot see how pci_msix_can_alloc_dyn() can return false when >> considering the VFIO PCI MSI-X flow: >> >> vfio_msi_enable(..., ..., msix == true) >> pci_alloc_irq_vectors(..., ..., ..., flag == PCI_IRQ_MSIX) >> pci_alloc_irq_vectors_affinity() >> __pci_enable_msix_range() >> pci_setup_msix_device_domain() >> pci_create_device_domain(..., &pci_msix_template, ...) >> >> The template used above, pci_msix_template, has MSI_FLAG_PCI_MSIX_ALLOC_DYN >> hardcoded. This is the flag that pci_msix_can_alloc_dyn() tests for. >> >> If indeed pci_msix_can_alloc_dyn() can return false in the VFIO PCI MSI-X >> usage then this series needs to be reworked to continue supporting >> existing allocation mechanism as well as dynamic MSI-X allocation. Which >> allocation mechanism to use would be depend on pci_msix_can_alloc_dyn(). >> >> Alternatively, if you agree that VFIO PCI MSI-X can expect >> pci_msix_can_alloc_dyn() to always return true then I should perhaps >> add a test in vfio_msi_enable() that confirms this is the case. This would >> cause vfio_msi_enable() to fail if dynamic MSI-X is not possible, perhaps even >> complain loudly with a WARN. > > pci_setup_msix_device_domain() says it returns true if: > > * True when: > * - The device does not have a MSI parent irq domain associated, > * which keeps the legacy architecture specific and the global > * PCI/MSI domain models working > * - The MSI-X domain exists already > * - The MSI-X domain was successfully allocated > > That first one seems concerning, dynamic allocation only works on irq > domain configurations. What does that exclude and do we care about any > of them for vfio-pci? Minimally this suggests a dependency on > IRQ_DOMAIN, which we don't currently have, but I'm not sure if > supporting irq domains is the same as having irq domains. Thanks, Just to confirm, as I mentioned in [1] I do plan to rework this solution to support both allocation mechanisms, using pci_msix_can_alloc_dyn() to pick which one to use. Thank you very much for pointing out this gap to me. Reinette [1] https://lore.kernel.org/lkml/e2d3f5a6-0a36-f19d-8f19-748197c3308d@xxxxxxxxx/
