Re: [PATCH] mm/vmemmap/devdax: Fix kernel crash when probing devdax devices

[Jane Chu <jane.chu@xxxxxxxxxx>]

On 4/7/2023 5:23 AM, Aneesh Kumar K.V wrote:
> diff --git a/mm/Kconfig b/mm/Kconfig
> index ff7b209dec05..99f87c1be1e8 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -461,6 +461,9 @@ config SPARSEMEM_VMEMMAP
>   	  pfn_to_page and page_to_pfn operations.  This is the most
>   	  efficient option when sufficient kernel resources are available.
>   
> +config ARCH_WANT_OPTIMIZE_VMEMMAP
> +	bool
> +

Could this devdax specific config switch be added to drivers/dax/Kconfig 
? also, how about adding 'DAX' to the config switch name?

BTW, I noticed something minor and unrelated in the original commit 
(c4386bd8ee3a):

-static unsigned long pfn_next(unsigned long pfn)
+static unsigned long pfn_next(struct dev_pagemap *pgmap, unsigned long pfn)
 {
-       if (pfn % 1024 == 0)
+       if (pfn % (1024 << pgmap->vmemmap_shift))     <---- this line
                cond_resched();
-       return pfn + 1;
+       return pfn + pgmap_vmemmap_nr(pgmap);
+}

should be
+       if (pfn % (1024 * pgmap_vmemmap_nr(pgmap))
to be consistent.

thanks,
-jane