Re: [PATCH] mm/nvdimm: Use correct alignment when looking at first pfn from a region

[Dan Williams <dan.j.williams@intel.com>]

On Mon, May 13, 2019 at 7:55 PM Aneesh Kumar K.V
<aneesh.kumar@linux.ibm.com> wrote:
>
> We already add the start_pad to the resource->start but fails to section
> align the start. This make sure with altmap we compute the right first
> pfn when start_pad is zero and we are doing an align down of start address.
>
> Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
> ---
>  kernel/memremap.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/memremap.c b/kernel/memremap.c
> index a856cb5ff192..23d77b60e728 100644
> --- a/kernel/memremap.c
> +++ b/kernel/memremap.c
> @@ -59,9 +59,9 @@ static unsigned long pfn_first(struct dev_pagemap *pgmap)
>  {
>         const struct resource *res = &pgmap->res;
>         struct vmem_altmap *altmap = &pgmap->altmap;
> -       unsigned long pfn;
> +       unsigned long pfn = PHYS_PFN(res->start);
>
> -       pfn = res->start >> PAGE_SHIFT;
> +       pfn = SECTION_ALIGN_DOWN(pfn);

This does not seem right to me it breaks the assumptions of where the
first expected valid pfn occurs in the passed in range.