[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 <j...@groves.net>
---
 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