Re: [PATCH 2/2] arm/xen: Add misuse warning to virt_to_gfn

[Julien Grall <julien@xen.org>]

Hi Simon,

On 25/08/2020 10:31, Simon Leiner wrote:
> As virt_to_gfn uses virt_to_phys, it will return invalid addresses when
> used with vmalloc'd addresses. This patch introduces a warning, when
> virt_to_gfn is used in this way.
> 
> Signed-off-by: Simon Leiner <simon@leiner.me>
> ---
>   include/xen/arm/page.h | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/include/xen/arm/page.h b/include/xen/arm/page.h
> index d7f6af50e200..b0d303b633d0 100644
> --- a/include/xen/arm/page.h
> +++ b/include/xen/arm/page.h
> @@ -76,7 +76,11 @@ static inline unsigned long bfn_to_pfn(unsigned long bfn)
>   #define bfn_to_local_pfn(bfn)	bfn_to_pfn(bfn)
>   
>   /* VIRT <-> GUEST conversion */
> -#define virt_to_gfn(v)		(pfn_to_gfn(virt_to_phys(v) >> XEN_PAGE_SHIFT))
> +#define virt_to_gfn(v)                                                         \
> +	({                                                                     \
> +		WARN_ON_ONCE(is_vmalloc_addr(v));                              \

virt_to_gfn() will usually be called from generic code. WARN_ON_ONCE() 
will only catch one instance and it means we would have to fix the first 
instance and then re-run to catch the others.

So I think we want to switch to WARN_ON() here.

Cheers,

-- 
Julien Grall