Re: [PATCH V7 05/19] dax: Add dax_operations for use by fs-dax on fsdev dax

Ira Weiny
2026-02-13T21:20:02Z

John Groves wrote:
> From: John Groves <John@Groves.net>
>
> fsdev: Add dax_operations for use by famfs
>
> - These methods are based on pmem_dax_ops from drivers/nvdimm/pmem.c
> - fsdev_dax_direct_access() returns the hpa, pfn and kva. The kva was
> newly stored as dev_dax->virt_addr by dev_dax_probe().
> - The hpa/pfn are used for mmap (dax_iomap_fault()), and the kva is used
> for read/write (dax_iomap_rw())
> - fsdev_dax_recovery_write() and dev_dax_zero_page_range() have not been
> tested yet. I'm looking for suggestions as to how to test those.
> - dax-private.h: add dev_dax->cached_size, which fsdev needs to
> remember. The dev_dax size cannot change while a driver is bound
> (dev_dax_resize returns -EBUSY if dev->driver is set). Caching the size
> at probe time allows fsdev's direct_access path can use it without
> acquiring dax_dev_rwsem (which isn't exported anyway).
>
> Signed-off-by: John Groves <john@groves.net>

[snip]

> +
> +static long __fsdev_dax_direct_access(struct dax_device *dax_dev, pgoff_t pgoff,
> + long nr_pages, enum dax_access_mode mode, void **kaddr,
> + unsigned long *pfn)
> +{
> + struct dev_dax *dev_dax = dax_get_private(dax_dev);
> + size_t size = nr_pages << PAGE_SHIFT;
> + size_t offset = pgoff << PAGE_SHIFT;
> + void *virt_addr = dev_dax->virt_addr + offset;
> + phys_addr_t phys;
> + unsigned long local_pfn;
> +
> + WARN_ON(!dev_dax->virt_addr);

WARN_ON_ONCE. But frankly I'm pretty sure this is impossible to hit given
the probe call, so best remove it. Also yall already used dev_dax->virt_addr
above. And will hand back a bad address to the caller. So...

> +
> + phys = dax_pgoff_to_phys(dev_dax, pgoff, nr_pages << PAGE_SHIFT);
> + if (phys == -1) {
> + dev_dbg(&dev_dax->dev,
> + "pgoff (%#lx) out of range\n", pgoff);
> + return -ERANGE;

EFAULT?

Ira

[snip]