[RFC PATCH 1/5] vfio: Add UAPI for ZONE_DEVICE-backed P2P registration

[Pranjal Shrivastava <praan@google.com>]

Introduce VFIO_DEVICE_FEATURE_P2P_REGISTER to the VFIO_DEVICE_FEATURE
ioctl. This feature allows a privileged userspace process to register
a specific PCI BAR with the kernel's PCI P2P DMA provider framework.

Unlike the standard VFIO dmabuf exporter, this feature leverages the
pci-p2pdma infrastructure to manufacture ZONE_DEVICE struct pages for
the BAR.

Standard VFIO mmap() is not supported for BARs registered via this
interface. Users are instead expected to use the native p2pmem sysfs
interface for memory allocation and management.

Signed-off-by: Pranjal Shrivastava <praan@google.com>
---
 include/uapi/linux/vfio.h | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 5de618a3a5ee..adbac3f965eb 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -1534,6 +1534,21 @@ struct vfio_device_feature_dma_buf {
  */
 #define VFIO_DEVICE_FEATURE_MIG_PRECOPY_INFOv2  12
 
+/**
+ * Upon VFIO_DEVICE_FEATURE_SET register a PCI BAR with the kernel
+ * P2P DMA subsystem (pci-p2pdma).
+ *
+ * Once a BAR is registered, it will be added to the device's P2P
+ * pool and can be allocated via the standard sysfs p2pmem/allocate
+ * interface.
+ *
+ * Note: Standard VFIO mmap() of the BAR will be blocked once it is
+ * registered for native P2P.
+ *
+ * Return: 0 on success, -errno on failure.
+ */
+#define VFIO_DEVICE_FEATURE_P2P_REGISTER 13
+
 /* -------- API for Type1 VFIO IOMMU -------- */
 
 /**
-- 
2.54.0.1099.g489fc7bff1-goog