[PATCH v4 0/5] iommu: Enable user space IOPFs in non-PASID and non-svm cases

Joel Granados
2024-10-15T21:08:29Z

This series makes use of iommufd_hwpt_replace_device to execute
non-pasid/non-svm user space IOPFs. Our main motivation is to expand or
facilitate user-space driver driven device verification by enabling IOPF
without SVM/PASID.

What?
* Enable IO page fault handling in user space for a non-pasid, non-svm
and non-virtualised use case.
* Move IOMMU_IOPF configuration from INTEL_IOMMU_SVM into INTEL_IOMMU.
* Move all page request queue related logic to a new (prq.c) file.
* Remove PASID checks from PRQ event handling as well as PRQ
initialization.
* Allow execution of IOMMU_HWPT_ALLOC with a valid fault id
(IOMMU_HWPT_FAULT_ID_VALID)

Why?
The PCI ATS Extended Capability allows peripheral devices to
participate in the caching of translations when operating under an
IOMMU. Further, the ATS Page Request Interface (PRI) Extension allows
devices to handle missing mappings. Currently, PRI is mainly used in
the context of Shared Virtual Addressing, requiring support for the
Process Address Space Identifier (PASID) capability which is not
strictly necessary. Relaxing this requirement adds to the
possibilities available for user-space driver driver device
verification as well as for avoiding pinning.

Testing?
The non-svm IOPF interface is exercised by first initializing an IOPF
enabled IOAS and then reading the fault file descriptor. Pseudocode on
the IOPF initializing and handling is in [3] and [4] (using libvfn).

Supplementary repositories supporting this patchset:
1. A user space library libvfn [1] which is used for testing and
verification (see examples/iopf.c), and
2. Basic emulation of PCIe ATS/PRI and Intel VT-d PRQ in QEMU [2].

Changes in v4:
- Include the "trailers" from Kevin that I missed on V3
- Link to v3: https://lore.kernel.org/r/20241009-jag-iopfv8-v3-0-bd4271df5b2b@kernel.org

Changes in v3:
- Adjust wording in cover letter
- Include "_iommu_" in the prq Intel function names to be more in line
with functions in iommu.h file
- Rebase on top of 6.12-rc2
- Update my ID in e-mail, git author and my Signed-off-by.
- Link to v2: https://lore.kernel.org/r/20240913-jag-iopfv8-v2-0-dea01c2343bc@samsung.com

Changes in v2:
- Remove "nesting" from wording. This wording is left over from initial
versions that are now irrelevant.
- Dropped "iommu: init pasid array while doing domain_replace and iopf
is active" as the initialization of the pasid_array x-array happens
automatically when an iopf capable domain is replaced on a device.
- Corrected commit message in "iommu/vt-d: Separate page request queue
from SVM"
- Link to v1: https://lore.kernel.org/r/20240904-jag-iopfv8-v1-0-e3549920adf3@samsung.com

V1:
- This is the first version of the series after initial feedback from
the RFC [5].

Comments and feedback are greatly appreciated
Best

Joel

[1] https://github.com/SamsungDS/libvfn/tree/iommufd-fault-queue
[2] https://gitlab.com/birkelund/qemu/-/tree/pcie-ats-pri

[3] Initializing
```
int iopf_init(struct iommu_ioas *ioas, const char *bdf)
{
// open vfio device from bdf
int devfd = open('/dev/vfio/devices/VFIO_DEV', O_RDWR);

struct vfio_device_bind_iommufd bind = {
.argsz = sizeof(bind),
.flags = 0,
.iommufd = __iommufd,
};
ioctl(devfd, VFIO_DEVICE_BIND_IOMMUFD, &bind);

struct iommu_ioas *ioas = ioas;
struct vfio_device_attach_iommufd_pt attach_data = {
.argsz = sizeof(attach_data),
.flags = 0,
.pt_id = ioas->id,
};
ioctl(devfd, VFIO_DEVICE_ATTACH_IOMMUFD_PT, &attach_data);

struct iommu_fault_alloc fault = {
.size = sizeof(fault),
.flags = 0,
};
ioctl(__iommufd, IOMMU_FAULT_QUEUE_ALLOC, &fault);

struct iommu_hwpt_alloc fault_cmd = {
.size = sizeof(fault_cmd),
.flags = IOMMU_HWPT_FAULT_ID_VALID,
.dev_id = bind.out_devid,
.pt_id = ioas->id,
.data_len = 0,
.data_uptr = (uint64_t)NULL,
.fault_id = fault.out_fault_id,
.__reserved = 0,
};
ioctl(__iommufd, IOMMU_HWPT_ALLOC, &fault_cmd);

// This is a re-attach
struct vfio_device_attach_iommufd_pt attach = {
.argsz = sizeof(attach),
.flags = 0,
.pt_id = fault_cmd.out_hwpt_id
};
ioctl(dev_fd, VFIO_DEVICE_ATTACH_IOMMUFD_PT, &attach);
}
```

[4] Handling
```
int handle_iopf(void *vaddr, int len, uint64_t iova) {
exec_command(CMD)

int iopf_fd = fault_cmd.fault_id;

struct iommu_hwpt_pgfault pgfault = {0};
if(read(iopf_fd, &pgfault, sizeof(pgfault)) == 0);
return; // no page fault

ret = iommu_map_vaddr(__iommmufd, vaddr, len, &iova)
struct iommu_hwpt_page_response pgfault_response = {
.cookie = pgfault.cookie,
.code = ret ? IOMMUFD_PAGE_RESP_SUCCESS : IOMMUFD_PAGE_RESP_INVALID,
};

write(iopf_fd, &pgfault_response, sizeof(pgfault_response));

return;
}
```

[5] https://lore.kernel.org/20240826-iopf-for-all-v1-0-59174e6a7528@samsung.com

Signed-off-by: Joel Granados <j.granados@samsung.com>
---
Joel Granados (3):
iommu/vt-d: Separate page request queue from SVM
iommu: kconfig: Move IOMMU_IOPF into INTEL_IOMMU
iommufd: Enable PRI when doing the iommufd_hwpt_alloc

Klaus Jensen (2):
iommu/vt-d: Remove the pasid present check in prq_event_thread
iommu/vt-d: drop pasid requirement for prq initialization

drivers/iommu/intel/Kconfig | 2 +-
drivers/iommu/intel/Makefile | 2 +-
drivers/iommu/intel/iommu.c | 31 ++-
drivers/iommu/intel/iommu.h | 14 +-
drivers/iommu/intel/prq.c | 406 +++++++++++++++++++++++++++++++++++
drivers/iommu/intel/svm.c | 397 ----------------------------------
drivers/iommu/iommufd/hw_pagetable.c | 3 +-
7 files changed, 428 insertions(+), 427 deletions(-)
---
base-commit: 8cf0b93919e13d1e8d4466eb4080a4c4d9d66d7b
change-id: 20240904-jag-iopfv8-1577fd20422d

Best regards,
--
Joel Granados <joel.granados@kernel.org>