Re: [PATCH V3 2/9] dax/fsdev: fix multi-range offset in memory_failure handler

[Dave Jiang]

On 5/30/26 9:50 AM, John Groves wrote:
> From: John Groves 
> 
> Fix memory_failure offset calculation for multi-range devices. The old code
> subtracted ranges[0].range.start from the faulting PFN's physical address,
> which produces an incorrect (inflated) logical offset when the PFN falls in
> ranges[1] or beyond due to physical gaps between ranges. Add
> fsdev_pfn_to_offset() to walk the range list and compute the correct
> device-linear byte offset.
> 
> Fixes: d5406bd458b0a ("dax: add fsdev.c driver for fs-dax on character dax")
> Signed-off-by: John Groves 

Reviewed-by: Dave Jiang 

> ---
>  drivers/dax/fsdev.c | 17 -
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
> index 188b2526bee45..f315533b299e9 100644
> --- a/drivers/dax/fsdev.c
> +++ b/drivers/dax/fsdev.c
> @@ -135,11 +135,26 @@ static void fsdev_clear_ops(void *data)
>   * The core mm code in free_zone_device_folio() handles the wake_up_var()
>   * directly for this memory type.
>   */
> +static u64 fsdev_pfn_to_offset(struct dev_dax *dev_dax, unsigned long pfn)
> +{
> + phys_addr_t phys = PFN_PHYS(pfn);
> + u64 offset = 0;
> +
> + for (int i = 0; i < dev_dax->nr_range; i++) {
> + struct range *range = &dev_dax->ranges[i].range;
> +
> + if (phys >= range->start && phys <= range->end)
> + return offset + (phys - range->start);
> + offset += range_len(range);
> + }
> + return -1ULL;
> +}
> +
>  static int fsdev_pagemap_memory_failure(struct dev_pagemap *pgmap,
>   unsigned long pfn, unsigned long nr_pages, int mf_flags)
>  {
>   struct dev_dax *dev_dax = pgmap->owner;
> - u64 offset = PFN_PHYS(pfn) - dev_dax->ranges[0].range.start;
> + u64 offset = fsdev_pfn_to_offset(dev_dax, pfn);
>   u64 len = nr_pages << PAGE_SHIFT;
>  
>   return dax_holder_notify_failure(dev_dax->dax_dev, offset,

Re: [PATCH V3 2/9] dax/fsdev: fix multi-range offset in memory_failure handler

[Alison Schofield]

On Sat, May 30, 2026 at 04:50:42PM +, John Groves wrote:
> From: John Groves 
> 
> Fix memory_failure offset calculation for multi-range devices. The old code
> subtracted ranges[0].range.start from the faulting PFN's physical address,
> which produces an incorrect (inflated) logical offset when the PFN falls in
> ranges[1] or beyond due to physical gaps between ranges. Add
> fsdev_pfn_to_offset() to walk the range list and compute the correct
> device-linear byte offset.
> 
> Fixes: d5406bd458b0a ("dax: add fsdev.c driver for fs-dax on character dax")
> Signed-off-by: John Groves 
> ---

Reviewed-by: Alison Schofield 

[PATCH V3 2/9] dax/fsdev: fix multi-range offset in memory_failure handler

[John Groves]

From: John Groves 

Fix memory_failure offset calculation for multi-range devices. The old code
subtracted ranges[0].range.start from the faulting PFN's physical address,
which produces an incorrect (inflated) logical offset when the PFN falls in
ranges[1] or beyond due to physical gaps between ranges. Add
fsdev_pfn_to_offset() to walk the range list and compute the correct
device-linear byte offset.

Fixes: d5406bd458b0a ("dax: add fsdev.c driver for fs-dax on character dax")
Signed-off-by: John Groves 
---
 drivers/dax/fsdev.c | 17 -
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/drivers/dax/fsdev.c b/drivers/dax/fsdev.c
index 188b2526bee45..f315533b299e9 100644
--- a/drivers/dax/fsdev.c
+++ b/drivers/dax/fsdev.c
@@ -135,11 +135,26 @@ static void fsdev_clear_ops(void *data)
  * The core mm code in free_zone_device_folio() handles the wake_up_var()
  * directly for this memory type.
  */
+static u64 fsdev_pfn_to_offset(struct dev_dax *dev_dax, unsigned long pfn)
+{
+   phys_addr_t phys = PFN_PHYS(pfn);
+   u64 offset = 0;
+
+   for (int i = 0; i < dev_dax->nr_range; i++) {
+   struct range *range = &dev_dax->ranges[i].range;
+
+   if (phys >= range->start && phys <= range->end)
+   return offset + (phys - range->start);
+   offset += range_len(range);
+   }
+   return -1ULL;
+}
+
 static int fsdev_pagemap_memory_failure(struct dev_pagemap *pgmap,
unsigned long pfn, unsigned long nr_pages, int mf_flags)
 {
struct dev_dax *dev_dax = pgmap->owner;
-   u64 offset = PFN_PHYS(pfn) - dev_dax->ranges[0].range.start;
+   u64 offset = fsdev_pfn_to_offset(dev_dax, pfn);
u64 len = nr_pages << PAGE_SHIFT;
 
return dax_holder_notify_failure(dev_dax->dax_dev, offset,
-- 
2.53.0