Re: [PATCH v18 2/2] xen/arm: check read handler behavior

[Julien Grall <julien@xxxxxxx>]

Hi Steward,

On 25/03/2025 17:27, Stewart Hildebrand wrote:
> We expect mmio read handlers to leave the bits above the access size
> zeroed. Add an ASSERT to check this aspect of read handler behavior.
>
> Suggested-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> Signed-off-by: Stewart Hildebrand <stewart.hildebrand@xxxxxxx>
With one question below:

Acked-by: Julien Grall <jgrall@xxxxxxxxxx>

> ---
> v17->v18:
> * no change
>
> v16->v17:
> * new patch
>
> See 
> https://lore.kernel.org/xen-devel/bc6660ef-59f1-4514-9792-067d987e3fbc@xxxxxxx/
>
> Also see 7db7bd0f319f ("arm/vpci: honor access size when returning an error")
>
> Also see xen/arch/arm/ioreq.c:handle_ioserv()
> ---
>   xen/arch/arm/io.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/xen/arch/arm/io.c b/xen/arch/arm/io.c
> index 653428e16c1f..68b5dca70026 100644
> --- a/xen/arch/arm/io.c
> +++ b/xen/arch/arm/io.c
> @@ -37,6 +37,8 @@ static enum io_state handle_read(const struct mmio_handler 
> *handler,
>       if ( !handler->ops->read(v, info, &r, handler->priv) )
>           return IO_ABORT;
>   
> +    ASSERT((r & ~GENMASK_ULL((1U << info->dabt.size) * 8 - 1, 0)) == 0);
OOI, I was expecing GENMASK to be sufficient because "r" is effectively 
an "unsigned long". So any reason to use GENMASK_ULL?
Cheers,

--
Julien Grall