Re: [XEN PATCH v7 08/20] xen/arm: ffa: note dependency on 4k pages

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

HI Jens,

> On 22 Feb 2023, at 16:33, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> 
> Adds a BUILD_BUG_ON() to assert the dependency on 4k pages in the FF-A
> mediator.
> 
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>

NIT: I would s/note/enforce/ in the title:
xen/arm: ffa: enforce 4k pages

Reviewed-by: Bertrand Marquis <bertrand.marquis@xxxxxxx>

Cheers
Bertrand

> ---
> xen/arch/arm/tee/ffa.c | 21 +++++++++++++++++++++
> 1 file changed, 21 insertions(+)
> 
> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> index d04bac9cc47f..8b0b80ce1ff5 100644
> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -56,6 +56,16 @@
> #define FFA_MY_VERSION          MAKE_FFA_VERSION(FFA_MY_VERSION_MAJOR, \
>                                                  FFA_MY_VERSION_MINOR)
> 
> +/*
> + * The FF-A specification explicitly works with 4K pages as a measure of
> + * memory size, for example, FFA_RXTX_MAP takes one parameter "RX/TX page
> + * count" which is the number of contiguous 4K pages allocated. Xen may use
> + * a different page size depending on the configuration to avoid confusion
> + * with PAGE_SIZE use a special define when it's a page size as in the FF-A
> + * specification.
> + */
> +#define FFA_PAGE_SIZE                   SZ_4K
> +
> /* Framework direct request/response */
> #define FFA_MSG_FLAG_FRAMEWORK          BIT(31, U)
> #define FFA_MSG_TYPE_MASK               0xFFU;
> @@ -242,6 +252,17 @@ static bool ffa_probe(void)
>     unsigned int major_vers;
>     unsigned int minor_vers;
> 
> +    /*
> +     * FF-A often works in units of 4K pages and currently it's assumed
> +     * that we can map memory using that granularity. See also the comment
> +     * above the FFA_PAGE_SIZE define.
> +     *
> +     * It is possible to support a PAGE_SIZE larger than 4K in Xen, but
> +     * until that is fully handled in this code make sure that we only use
> +     * 4K page sizes.
> +     */
> +    BUILD_BUG_ON(PAGE_SIZE != FFA_PAGE_SIZE);
> +
>     /*
>      * psci_init_smccc() updates this value with what's reported by EL-3
>      * or secure world.
> -- 
> 2.34.1
>