Re: [PATCH V3 1/2] mm/ioremap: Check virtual address alignment while creating huge mappings

["Kani, Toshi" <toshi.kani@hpe.com>]

On Thu, 2019-05-09 at 10:16 +0530, Anshuman Khandual wrote:
> Virtual address alignment is essential in ensuring correct clearing for all
> intermediate level pgtable entries and freeing associated pgtable pages. An
> unaligned address can end up randomly freeing pgtable page that potentially
> still contains valid mappings. Hence also check it's alignment along with
> existing phys_addr check.
> 
> Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Toshi Kani <toshi.kani@hpe.com>
> Cc: Andrew Morton <akpm@linux-foundation.org>
> Cc: Will Deacon <will.deacon@arm.com>
> Cc: Chintan Pandya <cpandya@codeaurora.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> ---
>  lib/ioremap.c | 6 ++++++
>  1 file changed, 6 insertions(+)
> 
> diff --git a/lib/ioremap.c b/lib/ioremap.c
> index 063213685563..8b5c8dda857d 100644
> --- a/lib/ioremap.c
> +++ b/lib/ioremap.c
> @@ -86,6 +86,9 @@ static int ioremap_try_huge_pmd(pmd_t *pmd, unsigned long addr,
>  	if ((end - addr) != PMD_SIZE)
>  		return 0;
>  
> +	if (!IS_ALIGNED(addr, PMD_SIZE))
> +		return 0;
> +
>  	if (!IS_ALIGNED(phys_addr, PMD_SIZE))
>  		return 0;
>  
> @@ -126,6 +129,9 @@ static int ioremap_try_huge_pud(pud_t *pud, unsigned long addr,
>  	if ((end - addr) != PUD_SIZE)
>  		return 0;
>  
> +	if (!IS_ALIGNED(addr, PUD_SIZE))
> +		return 0;
> +
>  	if (!IS_ALIGNED(phys_addr, PUD_SIZE))
>  		return 0;

Not sure if we have such case today, but I agree that it is prudent to
have such checks.  Is there any reason not to add this check to p4d for
consistency?

Thanks,
-Toshi