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

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.

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_* */