Re: [PATCH v3 02/13] device/dax: update devdax to use mmap_prepare

Pedro Falcato
2025-09-17T10:37:23Z

On Tue, Sep 16, 2025 at 03:11:48PM +0100, Lorenzo Stoakes wrote:
> The devdax driver does nothing special in its f_op->mmap hook, so
> straightforwardly update it to use the mmap_prepare hook instead.
>
> Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
> Acked-by: David Hildenbrand <david@redhat.com>
> Reviewed-by: Jan Kara <jack@suse.cz>

Acked-by: Pedro Falcato <pfalcato@suse.de>

> ---
> drivers/dax/device.c | 32 +++++++++++++++++++++-----------
> 1 file changed, 21 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/dax/device.c b/drivers/dax/device.c
> index 2bb40a6060af..c2181439f925 100644
> --- a/drivers/dax/device.c
> +++ b/drivers/dax/device.c
> @@ -13,8 +13,9 @@
> #include "dax-private.h"
> #include "bus.h"
>
> -static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> - const char *func)
> +static int __check_vma(struct dev_dax *dev_dax, vm_flags_t vm_flags,
> + unsigned long start, unsigned long end, struct file *file,
> + const char *func)
> {
> struct device *dev = &dev_dax->dev;
> unsigned long mask;
> @@ -23,7 +24,7 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> return -ENXIO;
>
> /* prevent private mappings from being established */
> - if ((vma->vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
> + if ((vm_flags & VM_MAYSHARE) != VM_MAYSHARE) {
> dev_info_ratelimited(dev,
> "%s: %s: fail, attempted private mapping\n",
> current->comm, func);
> @@ -31,15 +32,15 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> }
>
> mask = dev_dax->align - 1;
> - if (vma->vm_start & mask || vma->vm_end & mask) {
> + if (start & mask || end & mask) {
> dev_info_ratelimited(dev,
> "%s: %s: fail, unaligned vma (%#lx - %#lx, %#lx)\n",
> - current->comm, func, vma->vm_start, vma->vm_end,
> + current->comm, func, start, end,
> mask);
> return -EINVAL;
> }
>
> - if (!vma_is_dax(vma)) {
> + if (!file_is_dax(file)) {
> dev_info_ratelimited(dev,
> "%s: %s: fail, vma is not DAX capable\n",
> current->comm, func);
> @@ -49,6 +50,13 @@ static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> return 0;
> }
>
> +static int check_vma(struct dev_dax *dev_dax, struct vm_area_struct *vma,
> + const char *func)
> +{
> + return __check_vma(dev_dax, vma->vm_flags, vma->vm_start, vma->vm_end,
> + vma->vm_file, func);
> +}
> +

Side comment: I'm no DAX expert at all, but this check_vma() thing looks... smelly?
Besides the !dax_alive() check, I don't see the need to recheck vma limits at
every ->huge_fault() call. Even taking mremap() into account,
->get_unmapped_area() should Do The Right Thing, no?

--
Pedro