uio: Add SVA support for PCI devices via uio_pci_generic_sva.c

This patch introduces a new UIO driver, uio_pci_generic_sva, which
extends the functionality of uio_pci_generic by adding support for
Shared Virtual Addressing (SVA) when IOMMU is enabled in the system.

The key enhancement allows PCI devices to directly use user-space virtual
addresses for DMA operations, eliminating the need for bounce buffers or
explicit IOVA mapping. This is achieved by leveraging the kernel's IOMMU-SVA
subsystem, including process address space attachment, page fault handling,
and shared context management between CPU and device.

With this driver, userspace applications can perform zero-copy DMA using
native pointers:

   void *addr = malloc(N);
   set_dma_addr((uint64_t)addr);  // Passing user VA directly
   start_dma();

The device can now access 'addr' through the IOMMU's PASID-based translation,
provided that the underlying IOMMU hardware (e.g., Intel VT-d 3.1+, AMD-Vi,
ARM SMMU, RISCV IOMMU) and platform support SVA.

Dependencies:
- CONFIG_IOMMU_SVA must be enabled.
- The platform must support PRI (Page Request Interface) and PASID.
- Device drivers/userspace must handle page faults if demand-paging is used.

The implementation reuses core logic from uio_pci_generic.c while adding
PASID setting, and integration with the IOMMU SVA APIs.

Also, add a read-only sysfs attribute 'pasid' to expose the Process Address
Space ID assigned by IOMMU driver when binding an SVA-enabled device.
For details, refer to the ABI documentation for uio_pci_sva driver sysfs attribute
(Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid).

Signed-off-by: Yaxing Guo <guoyaxing@bosc.ac.cn>
Link: https://patch.msgid.link/20250926095828.506-1-guoyaxing@bosc.ac.cn
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 29 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid b/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid
new file mode 100644
index 000000000000..6892fe46cea8
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-uio_pci_sva-pasid
@@ -0,0 +1,29 @@
+What:		/sys/bus/pci/drivers/uio_pci_sva/<pci_dev>/pasid
+Date:		September 2025
+Contact:	Yaxing Guo <guoyaxing@bosc.ac.cn>
+Description:
+		Process Address Space ID (PASID) assigned by IOMMU driver to
+		the device for use with Shared Virtual Addressing (SVA).
+
+		This read-only attribute exposes the PASID (A 20-bit identifier
+		used in PCIe Address Translation Services and iommu table walks)
+		allocated by the IOMMU driver during sva device binding.
+
+		User-space UIO applications must read this attribute to obtain
+		the PASID and program it into the device's configuration registers.
+		This enables the device to perform DMA using user-space virtual
+		address, with address translation handled by IOMMU.
+
+		UIO User-space applications must:
+		- Opening device and Mapping the device's register space via /dev/uioX
+		(This triggers the IOMMU driver to allocate the PASID)
+		- Reading the PASID from sysfs
+		- Writing the PASID to a device-specific register (with example offset)
+		The code may be like:
+
+		map = mmap(..., "/dev/uio0", ...);
+
+		f = fopen("/sys/.../pasid", "r");
+		fscanf(f, "%d", &pasid);
+
+		map[REG_PASID_OFFSET] = pasid;