Re: [libvirt] [RFC PATCH 4/9] vfio-pci: register default dynamic-trap-bar-info region

On Wed, 4 Dec 2019 22:26:50 -0500 Yan Zhao <yan.y.zhao(a)intel.com&gt; wrote: > Dynamic trap bar info region is a channel for QEMU and vendor driver to > communicate dynamic trap info. It is of type > VFIO_REGION_TYPE_DYNAMIC_TRAP_BAR_INFO and subtype > VFIO_REGION_SUBTYPE_DYNAMIC_TRAP_BAR_INFO. > > This region has two fields: dt_fd and trap. > When QEMU detects a device regions of this type, it will create an > eventfd and write its eventfd id to dt_fd field. > When vendor drivre signals this eventfd, QEMU reads trap field of this > info region. > - If trap is true, QEMU would search the device's PCI BAR > regions and disable all the sparse mmaped subregions (if the sparse > mmaped subregion is disablable). > - If trap is false, QEMU would re-enable those subregions. > > A typical usage is > 1. vendor driver first cuts its bar 0 into several sections, all in a > sparse mmap array. So initally, all its bar 0 are passthroughed. > 2. vendor driver specifys part of bar 0 sections to be disablable. > 3. on migration starts, vendor driver signals dt_fd and set trap to true > to notify QEMU disabling the bar 0 sections of disablable flags on. > 4. QEMU disables those bar 0 section and hence let vendor driver be able > to trap access of bar 0 registers and make dirty page tracking possible. > 5. on migration failure, vendor driver signals dt_fd to QEMU again. > QEMU reads trap field of this info region which is false and QEMU > re-passthrough the whole bar 0 region. > > Vendor driver specifies whether it supports dynamic-trap-bar-info region > through cap VFIO_PCI_DEVICE_CAP_DYNAMIC_TRAP_BAR in > vfio_pci_mediate_ops->open(). > > If vfio-pci detects this cap, it will create a default > dynamic_trap_bar_info region on behalf of vendor driver with region len=0 > and region->ops=null. > Vvendor driver should override this region's len, flags, rw, mmap in its > vfio_pci_mediate_ops. TBH, I don't like this interface at all. Userspace doesn't pass data to the kernel via INFO ioctls. We have a SET_IRQS ioctl for configuring user signaling with eventfds. I think we only need to define an IRQ type that tells the user to re-evaluate the sparse mmap information for a region. The user would enumerate the device IRQs via GET_IRQ_INFO, find one of this type where the IRQ info would also indicate which region(s) should be re-evaluated on signaling. The user would enable that signaling via SET_IRQS and simply re-evaluate the

sparse mmap capability for the associated regions when signaled.

Thanks, Alex

> > Cc: Kevin Tian <kevin.tian(a)intel.com&gt; > > Signed-off-by: Yan Zhao <yan.y.zhao(a)intel.com&gt; > --- > drivers/vfio/pci/vfio_pci.c | 16 ++++++++++++++++ > include/linux/vfio.h | 3 ++- > include/uapi/linux/vfio.h | 11 +++++++++++ > 3 files changed, 29 insertions(+), 1 deletion(-) > > diff --git a/drivers/vfio/pci/vfio_pci.c b/drivers/vfio/pci/vfio_pci.c > index 059660328be2..62b811ca43e4 100644 > --- a/drivers/vfio/pci/vfio_pci.c > +++ b/drivers/vfio/pci/vfio_pci.c > @@ -127,6 +127,19 @@ void init_migration_region(struct vfio_pci_device *vdev) > NULL); > } > > +/** > + * register a region to hold info for dynamically trap bar regions > + */ > +void init_dynamic_trap_bar_info_region(struct vfio_pci_device *vdev) > +{ > + vfio_pci_register_dev_region(vdev, > + VFIO_REGION_TYPE_DYNAMIC_TRAP_BAR_INFO, > + VFIO_REGION_SUBTYPE_DYNAMIC_TRAP_BAR_INFO, > + NULL, 0, > + VFIO_REGION_INFO_FLAG_READ | VFIO_REGION_INFO_FLAG_WRITE, > + NULL); > +} > + > static void vfio_pci_probe_mmaps(struct vfio_pci_device *vdev) > { > struct resource *res; > @@ -538,6 +551,9 @@ static int vfio_pci_open(void *device_data) > if (caps & VFIO_PCI_DEVICE_CAP_MIGRATION) > init_migration_region(vdev); > > + if (caps & VFIO_PCI_DEVICE_CAP_DYNAMIC_TRAP_BAR) > + init_dynamic_trap_bar_info_region(vdev); > + > pr_info("vfio pci found mediate_ops %s, caps=%llx, handle=%x for %x:%x\n", > vdev->mediate_ops->name, caps, > handle, vdev->pdev->vendor, > diff --git a/include/linux/vfio.h b/include/linux/vfio.h > index cddea8e9dcb2..cf8ecf687bee 100644 > --- a/include/linux/vfio.h > +++ b/include/linux/vfio.h > @@ -197,7 +197,8 @@ extern void vfio_virqfd_disable(struct virqfd **pvirqfd); > > struct vfio_pci_mediate_ops { > char *name; > -#define VFIO_PCI_DEVICE_CAP_MIGRATION (0x01) > +#define VFIO_PCI_DEVICE_CAP_MIGRATION (0x01) > +#define VFIO_PCI_DEVICE_CAP_DYNAMIC_TRAP_BAR (0x02) > int (*open)(struct pci_dev *pdev, u64 *caps, u32 *handle); > void (*release)(int handle); > void (*get_region_info)(int handle, > diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h > index caf8845a67a6..74a2d0b57741 100644 > --- a/include/uapi/linux/vfio.h > +++ b/include/uapi/linux/vfio.h > @@ -258,6 +258,9 @@ struct vfio_region_info { > struct vfio_region_sparse_mmap_area { > __u64 offset; /* Offset of mmap'able area within region */ > __u64 size; /* Size of mmap'able area */ > + __u32 disablable; /* whether this mmap'able are able to > + * be dynamically disabled > + */ > }; > > struct vfio_region_info_cap_sparse_mmap { > @@ -454,6 +457,14 @@ struct vfio_device_migration_info { > #define VFIO_DEVICE_DIRTY_PFNS_ALL (~0ULL) > } __attribute__((packed)); > > +/* Region type and sub-type to hold info to dynamically trap bars */ > +#define VFIO_REGION_TYPE_DYNAMIC_TRAP_BAR_INFO (4) > +#define VFIO_REGION_SUBTYPE_DYNAMIC_TRAP_BAR_INFO (1) > + > +struct vfio_device_dt_bar_info_region { > + __u32 dt_fd; /* fd of eventfd to notify qemu trap/untrap bars*/ > + __u32 trap; /* trap/untrap bar regions */ > +}; > > /* sub-types for VFIO_REGION_TYPE_PCI_* */ >