[RFC PATCH 04/20] dev_dax_iomap: Save the kva from memremap

[John Groves]

Save the kva from memremap because we need it for iomap rw support

Prior to famfs, there were no iomap users of /dev/dax - so the virtual
address from memremap was not needed.

Also: in some cases dev_dax_probe() is called with the first
dev_dax->range offset past pgmap[0].range. In those cases we need to
add the difference to virt_addr in order to have the physaddr's in
dev_dax->ranges match dev_dax->virt_addr.

Dragons...

Signed-off-by: John Groves <john@xxxxxxxxxx>
---
 drivers/dax/dax-private.h |  1 +
 drivers/dax/device.c      | 15 +++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/drivers/dax/dax-private.h b/drivers/dax/dax-private.h
index 446617b73aea..894eb1c66b4a 100644
--- a/drivers/dax/dax-private.h
+++ b/drivers/dax/dax-private.h
@@ -63,6 +63,7 @@ struct dax_mapping {
 struct dev_dax {
 	struct dax_region *region;
 	struct dax_device *dax_dev;
+	u64 virt_addr;
 	unsigned int align;
 	int target_node;
 	bool dyn_id;
diff --git a/drivers/dax/device.c b/drivers/dax/device.c
index 40ba660013cf..6cd79d00fe1b 100644
--- a/drivers/dax/device.c
+++ b/drivers/dax/device.c
@@ -372,6 +372,7 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	struct dax_device *dax_dev = dev_dax->dax_dev;
 	struct device *dev = &dev_dax->dev;
 	struct dev_pagemap *pgmap;
+	u64 data_offset = 0;
 	struct inode *inode;
 	struct cdev *cdev;
 	void *addr;
@@ -426,6 +427,20 @@ static int dev_dax_probe(struct dev_dax *dev_dax)
 	if (IS_ERR(addr))
 		return PTR_ERR(addr);
 
+	/* Detect whether the data is at a non-zero offset into the memory */
+	if (pgmap->range.start != dev_dax->ranges[0].range.start) {
+		u64 phys = (u64)dev_dax->ranges[0].range.start;
+		u64 pgmap_phys = (u64)dev_dax->pgmap[0].range.start;
+		u64 vmemmap_shift = (u64)dev_dax->pgmap[0].vmemmap_shift;
+
+		if (!WARN_ON(pgmap_phys > phys))
+			data_offset = phys - pgmap_phys;
+
+		pr_notice("%s: offset detected phys=%llx pgmap_phys=%llx offset=%llx shift=%llx\n",
+		       __func__, phys, pgmap_phys, data_offset, vmemmap_shift);
+	}
+	dev_dax->virt_addr = (u64)addr + data_offset;
+
 	inode = dax_inode(dax_dev);
 	cdev = inode->i_cdev;
 	cdev_init(cdev, &dax_fops);
-- 
2.43.0