[PATCH kernel RFC 4/4] vfio/spapr_tce: Advertise and allow a huge DMA windows at 4GB

[Alexey Kardashevskiy]

So far the only option for a big 64big DMA window was a window located
at 0x800.0000.0000.0000 (1<<59) which creates problems for devices
supporting smaller DMA masks.

This exploits a POWER9 PHB option to allow the second DMA window to map
at 0 and advertises it with a 4GB offset to avoid overlap with
the default 32bit window.

Signed-off-by: Alexey Kardashevskiy <aik at ozlabs.ru>
---


This is an additional option and not inside
vfio_iommu_spapr_tce_ddw_info as the new option gets
a new flag and one would expect a new member in
vfio_iommu_spapr_tce_info per a flag but can squash it
into vfio_iommu_spapr_tce_ddw_info, should I?


---
 include/uapi/linux/vfio.h           |  2 ++
 drivers/vfio/vfio_iommu_spapr_tce.c | 10 ++++++++--
 2 files changed, 10 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/vfio.h b/include/uapi/linux/vfio.h
index 9e843a147ead..c7f89d47335a 100644
--- a/include/uapi/linux/vfio.h
+++ b/include/uapi/linux/vfio.h
@@ -831,9 +831,11 @@ struct vfio_iommu_spapr_tce_info {
 	__u32 argsz;
 	__u32 flags;
 #define VFIO_IOMMU_SPAPR_INFO_DDW	(1 << 0)	/* DDW supported */
+#define VFIO_IOMMU_SPAPR_INFO_DDW_START	(1 << 1)	/* DDW offset */
 	__u32 dma32_window_start;	/* 32 bit window start (bytes) */
 	__u32 dma32_window_size;	/* 32 bit window size (bytes) */
 	struct vfio_iommu_spapr_tce_ddw_info ddw;
+	__u64 dma64_window_start;
 };
 
 #define VFIO_IOMMU_SPAPR_TCE_GET_INFO	_IO(VFIO_TYPE, VFIO_BASE + 12)
diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
index 26cef65b41e7..470008c3359f 100644
--- a/drivers/vfio/vfio_iommu_spapr_tce.c
+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
@@ -691,7 +691,7 @@ static long tce_iommu_create_window(struct tce_container *container,
 	container->tables[num] = tbl;
 
 	/* Return start address assigned by platform in create_table() */
-	*start_addr = tbl->it_offset << tbl->it_page_shift;
+	*start_addr = tbl->it_dmaoff << tbl->it_page_shift;
 
 	return 0;
 
@@ -842,7 +842,13 @@ static long tce_iommu_ioctl(void *iommu_data,
 			info.ddw.levels = table_group->max_levels;
 		}
 
-		ddwsz = offsetofend(struct vfio_iommu_spapr_tce_info, ddw);
+		ddwsz = offsetofend(struct vfio_iommu_spapr_tce_info,
+				dma64_window_start);
+
+		if (info.argsz >= ddwsz) {
+			info.flags |= VFIO_IOMMU_SPAPR_INFO_DDW_START;
+			info.dma64_window_start = table_group->tce64_start;
+		}
 
 		if (info.argsz >= ddwsz)
 			minsz = ddwsz;
-- 
2.17.1