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

[Jens Wiklander <jens.wiklander@xxxxxxxxxx>]

Hi Bertrand,

On Fri, Feb 24, 2023 at 4:27 PM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> 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

OK, I'll fix it.

Thanks,
Jens

>
> 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
> >
>