[PATCH RFC v2 09/15] vfio/nvgrace-egm: Add chardev ops for EGM management

[ankita]

From: Ankit Agrawal <ankita@xxxxxxxxxx>

EGM module implements the mmap file_ops to manage the usermode app's
VMA mapping to the EGM region. The appropriate region is determined
from the minor number.

Note that the EGM memory region is invisible to the host kernel as it
is not present in the host EFI map. The host Linux MM thus cannot manage
the memory, even though it is accessible on the host SPA. The EGM module
thus use remap_pfn_range() to perform the VMA mapping to the EGM region.

Suggested-by: Aniket Agashe <aniketa@xxxxxxxxxx>
Signed-off-by: Ankit Agrawal <ankita@xxxxxxxxxx>
---
 drivers/vfio/pci/nvgrace-gpu/egm.c | 41 +++++++++++++++++++++++++++++-
 include/linux/nvgrace-egm.h        |  1 +
 2 files changed, 41 insertions(+), 1 deletion(-)

diff --git a/drivers/vfio/pci/nvgrace-gpu/egm.c b/drivers/vfio/pci/nvgrace-gpu/egm.c
index d7e4f61a241c..5786ebe374a5 100644
--- a/drivers/vfio/pci/nvgrace-gpu/egm.c
+++ b/drivers/vfio/pci/nvgrace-gpu/egm.c
@@ -17,19 +17,58 @@ struct chardev {
 	struct cdev cdev;
 };
 
+static struct nvgrace_egm_dev *
+egm_chardev_to_nvgrace_egm_dev(struct chardev *egm_chardev)
+{
+	struct auxiliary_device *aux_dev =
+		container_of(egm_chardev->device.parent, struct auxiliary_device, dev);
+
+	return container_of(aux_dev, struct nvgrace_egm_dev, aux_dev);
+}
+
 static int nvgrace_egm_open(struct inode *inode, struct file *file)
 {
+	struct chardev *egm_chardev =
+		container_of(inode->i_cdev, struct chardev, cdev);
+
+	file->private_data = egm_chardev;
+
 	return 0;
 }
 
 static int nvgrace_egm_release(struct inode *inode, struct file *file)
 {
+	file->private_data = NULL;
+
 	return 0;
 }
 
 static int nvgrace_egm_mmap(struct file *file, struct vm_area_struct *vma)
 {
-	return 0;
+	struct chardev *egm_chardev = file->private_data;
+	struct nvgrace_egm_dev *egm_dev =
+		egm_chardev_to_nvgrace_egm_dev(egm_chardev);
+	u64 req_len, pgoff, end;
+	unsigned long start_pfn;
+
+	pgoff = vma->vm_pgoff &
+		((1U << (EGM_OFFSET_SHIFT - PAGE_SHIFT)) - 1);
+
+	if (check_sub_overflow(vma->vm_end, vma->vm_start, &req_len) ||
+	    check_add_overflow(PHYS_PFN(egm_dev->egmphys), pgoff, &start_pfn) ||
+	    check_add_overflow(PFN_PHYS(pgoff), req_len, &end))
+		return -EOVERFLOW;
+
+	if (end > egm_dev->egmlength)
+		return -EINVAL;
+
+	/*
+	 * EGM memory is invisible to the host kernel and is not managed
+	 * by it. Map the usermode VMA to the EGM region.
+	 */
+	return remap_pfn_range(vma, vma->vm_start,
+			       start_pfn, req_len,
+			       vma->vm_page_prot);
 }
 
 static const struct file_operations file_ops = {
diff --git a/include/linux/nvgrace-egm.h b/include/linux/nvgrace-egm.h
index a66906753267..b9956e7e5a0e 100644
--- a/include/linux/nvgrace-egm.h
+++ b/include/linux/nvgrace-egm.h
@@ -9,6 +9,7 @@
 #include <linux/auxiliary_bus.h>
 
 #define NVGRACE_EGM_DEV_NAME "egm"
+#define EGM_OFFSET_SHIFT   40
 
 struct gpu_node {
 	struct list_head list;
-- 
2.34.1