On Thu, 24 Jun 2021 04:20:31 +0200 Thomas Gleixner <tglx@xxxxxxxxxxxxx> wrote: > Kevin, > > thank you very much for digging into this! You made my day! > > On Thu, Jun 24 2021 at 00:00, Kevin Tian wrote: > >> From: Alex Williamson <alex.williamson@xxxxxxxxxx> > >> To work with what we've got, the vfio API describes the limitation of > >> the host interfaces via the VFIO_IRQ_INFO_NORESIZE flag. QEMU then > >> makes a choice in an attempt to better reflect what we can infer of the > >> guest programming of the device to incrementally enable vectors. We > > > > It's a surprise to me that Qemu even doesn't look at this flag today after > > searching its code... > > Indeed. > > git clone https://github.com/qemu/qemu.git > cd qemu > git log -p | grep NORESIZE > + * The NORESIZE flag indicates that the interrupt lines within the index > +#define VFIO_IRQ_INFO_NORESIZE (1 << 3) > > According to the git history of QEMU this was never used at all and I > don't care about the magic muck which might be in some RHT repository > which might make use of that. > > Find below the proper fix for this nonsense which just wasted everyones > time. I'll post it officialy with a proper changelog tomorrow unless > Kevin beats me to it who actually unearthed this and surely earns the > credit. > > Alex, I seriously have to ask what you were trying to tell us about this > flag and it's great value and the design related to this. > > I'm sure you can submit the corresponding fix to qemu yourself. > > And once you are back from lala land, can you please explain how > VFIO/PCI/MSIX is supposed to work in reality? It's part of the spec, there's never been a case of !NORESIZE, assuming NORESIZE is the safe behavior. Sorry, there's no smoking gun here, NAK > --- > --- a/drivers/gpu/drm/i915/gvt/kvmgt.c > +++ b/drivers/gpu/drm/i915/gvt/kvmgt.c > @@ -1644,8 +1644,6 @@ static long intel_vgpu_ioctl(struct mdev > if (info.index == VFIO_PCI_INTX_IRQ_INDEX) > info.flags |= (VFIO_IRQ_INFO_MASKABLE | > VFIO_IRQ_INFO_AUTOMASKED); > - else > - info.flags |= VFIO_IRQ_INFO_NORESIZE; > > return copy_to_user((void __user *)arg, &info, minsz) ? > -EFAULT : 0; > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -1018,8 +1018,6 @@ static long vfio_pci_ioctl(struct vfio_d > if (info.index == VFIO_PCI_INTX_IRQ_INDEX) > info.flags |= (VFIO_IRQ_INFO_MASKABLE | > VFIO_IRQ_INFO_AUTOMASKED); > - else > - info.flags |= VFIO_IRQ_INFO_NORESIZE; > > return copy_to_user((void __user *)arg, &info, minsz) ? > -EFAULT : 0; > --- a/include/uapi/linux/vfio.h > +++ b/include/uapi/linux/vfio.h > @@ -693,16 +693,6 @@ struct vfio_region_info_cap_nvlink2_lnks > * automatically masked by VFIO and the user needs to unmask the line > * to receive new interrupts. This is primarily intended to distinguish > * level triggered interrupts. > - * > - * The NORESIZE flag indicates that the interrupt lines within the index > - * are setup as a set and new subindexes cannot be enabled without first > - * disabling the entire index. This is used for interrupts like PCI MSI > - * and MSI-X where the driver may only use a subset of the available > - * indexes, but VFIO needs to enable a specific number of vectors > - * upfront. In the case of MSI-X, where the user can enable MSI-X and > - * then add and unmask vectors, it's up to userspace to make the decision > - * whether to allocate the maximum supported number of vectors or tear > - * down setup and incrementally increase the vectors as each is enabled. > */ > struct vfio_irq_info { > __u32 argsz; > @@ -710,7 +700,6 @@ struct vfio_irq_info { > #define VFIO_IRQ_INFO_EVENTFD (1 << 0) > #define VFIO_IRQ_INFO_MASKABLE (1 << 1) > #define VFIO_IRQ_INFO_AUTOMASKED (1 << 2) > -#define VFIO_IRQ_INFO_NORESIZE (1 << 3) > __u32 index; /* IRQ index */ > __u32 count; /* Number of IRQs within this index */ > }; > --- a/samples/vfio-mdev/mtty.c > +++ b/samples/vfio-mdev/mtty.c > @@ -1092,9 +1092,6 @@ static int mtty_get_irq_info(struct mdev > if (irq_info->index == VFIO_PCI_INTX_IRQ_INDEX) > irq_info->flags |= (VFIO_IRQ_INFO_MASKABLE | > VFIO_IRQ_INFO_AUTOMASKED); > - else > - irq_info->flags |= VFIO_IRQ_INFO_NORESIZE; > - > return 0; > } > >
