[PATCH RFC v1 02/12] mm/usercopy.c: Prepare check_page_span() for PG_reserved changes

[David Hildenbrand]

On 22.10.19 19:12, David Hildenbrand wrote:
> Right now, ZONE_DEVICE memory is always set PG_reserved. We want to
> change that.
> 
> Let's make sure that the logic in the function won't change. Once we no
> longer set these pages to reserved, we can rework this function to
> perform separate checks for ZONE_DEVICE (split from PG_reserved checks).
> 
> Cc: Kees Cook <keescook at chromium.org>
> Cc: Andrew Morton <akpm at linux-foundation.org>
> Cc: Kate Stewart <kstewart at linuxfoundation.org>
> Cc: Allison Randal <allison at lohutok.net>
> Cc: "Isaac J. Manjarres" <isaacm at codeaurora.org>
> Cc: Qian Cai <cai at lca.pw>
> Cc: Thomas Gleixner <tglx at linutronix.de>
> Signed-off-by: David Hildenbrand <david at redhat.com>
> ---
>   mm/usercopy.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/usercopy.c b/mm/usercopy.c
> index 660717a1ea5c..a3ac4be35cde 100644
> --- a/mm/usercopy.c
> +++ b/mm/usercopy.c
> @@ -203,14 +203,15 @@ static inline void check_page_span(const void *ptr, unsigned long n,
>   	 * device memory), or CMA. Otherwise, reject since the object spans
>   	 * several independently allocated pages.
>   	 */
> -	is_reserved = PageReserved(page);
> +	is_reserved = PageReserved(page) || is_zone_device_page(page);
>   	is_cma = is_migrate_cma_page(page);
>   	if (!is_reserved && !is_cma)
>   		usercopy_abort("spans multiple pages", NULL, to_user, 0, n);
>   
>   	for (ptr += PAGE_SIZE; ptr <= end; ptr += PAGE_SIZE) {
>   		page = virt_to_head_page(ptr);
> -		if (is_reserved && !PageReserved(page))
> +		if (is_reserved && !(PageReserved(page) ||
> +				     is_zone_device_page(page)))
>   			usercopy_abort("spans Reserved and non-Reserved pages",
>   				       NULL, to_user, 0, n);
>   		if (is_cma && !is_migrate_cma_page(page))
> 

@Kees, would it be okay to stop checking against ZONE_DEVICE pages here 
or is there a good rationale behind this?

(I would turn this patch into a simple update of the comment if we agree 
that we don't care)

-- 

Thanks,

David / dhildenb