Re: [XEN PATCH v7 16/20] xen/arm: ffa: add defines for sharing memory

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jens,

> On 22 Feb 2023, at 16:33, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> 
> Adds defines needed for sharing using the function FFA_MEM_SHARE and
> friends.
> 
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
> xen/arch/arm/tee/ffa.c | 57 ++++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 57 insertions(+)
> 
> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> index 3571817c0bcd..bfd378f7fcd7 100644
> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -22,6 +22,14 @@
> #include <asm/tee/ffa.h>
> #include <asm/regs.h>
> 
> +/*
> + * References:
> + * FF-A-1.0-REL: FF-A specification version 1.0 available at
> + *               https://developer.arm.com/documentation/den0077/a
> + * FF-A-1.1-REL0: FF-A specification version 1.1 available at
> + *                https://developer.arm.com/documentation/den0077/e
> + */

This could actually be directly in the file header.

> +
> /* Error codes */
> #define FFA_RET_OK                      0
> #define FFA_RET_NOT_SUPPORTED           -1
> @@ -66,6 +74,55 @@
>  */
> #define FFA_PAGE_SIZE                   SZ_4K
> 
> +/*
> + * Limit for shared buffer size. Please note that this define limits
> + * number of pages. But user buffer can be not aligned to a page
> + * boundary. So it is possible that user would not be able to share
> + * exactly FFA_MAX_SHM_BUFFER_PG * FFA_PAGE_SIZE bytes.
> + *
> + * FF-A doesn't have any direct requirments on GlobalPlatform or vice
> + * versa, but an implementation can very well use FF-A in order to provide
> + * a GlobalPlatform interface on top.
> + *
> + * Global Platform specification for TEE requires that any TEE
> + * implementation should allow to share buffers with size of at least
> + * 512KB. Due to align issue mentioned above, we need to increase this
> + * value with one.

Could you give a bit more details here: what spec version, where in the spec ?

I did download one version of it and at a first glance could not find this 
value.

> + */
> +#define FFA_MAX_SHM_PAGE_COUNT          (SZ_512K / FFA_PAGE_SIZE + 1)
> +
> +/*
> + * Limits the number of shared buffers that guest can have at once. This
> + * is to prevent case, when guests tricks XEN into exhausting its own
> + * memory by allocating many small buffers. This value has been chosen
> + * arbitrary.
> + */
> +#define FFA_MAX_SHM_COUNT               32

For those 2 limits, I am a bit wondering which should be defined in the code or 
maybe
configurable in kconfig or through xen command line or per guest.

I do not think we can answer that now but if one of these limits is reached we 
should
have a clear error message so that we could easily say what to modify and decide
if/how to solve it.


> +
> +/* FF-A-1.1-REL0 section 10.9.2 Memory region handle, page 167 */
> +#define FFA_HANDLE_HYP_FLAG             BIT(63, ULL)
> +#define FFA_HANDLE_INVALID              0xffffffffffffffffULL
> +
> +/*
> + * The bits for FFA_NORMAL_MEM_REG_ATTR FFA_MEM_ACC_RW below are
> + * defined in FF-A-1.1-REL0 Table 10.18 at page 175.
> + */
> + /* Memory attributes: Normal memory, Write-Back cacheable, Inner shareable 
> */
> +#define FFA_NORMAL_MEM_REG_ATTR         0x2fU
> +/* Memory access permissions: Read-write */
> +#define FFA_MEM_ACC_RW                  0x2U

RW bits are defined in table 10.15 at page 168 if i am not mistaking

> +
> +/* FF-A-1.1-REL0 section 10.11.4 Flags usage, page 184-187 */
> +/* Clear memory before mapping in receiver */
> +#define FFA_MEMORY_REGION_FLAG_CLEAR            BIT(0, U)
> +/* Relayer may time slice this operation */
> +#define FFA_MEMORY_REGION_FLAG_TIME_SLICE       BIT(1, U)
> +/* Clear memory after receiver relinquishes it */
> +#define FFA_MEMORY_REGION_FLAG_CLEAR_RELINQUISH BIT(2, U)
> +/* Share memory transaction */
> +#define FFA_MEMORY_REGION_TRANSACTION_TYPE_SHARE (1U << 3)
> +
> +
Please only add one empty line here.

I checked the definitions and they are all coherent with the spec.

Cheers
Bertrand

> /* Framework direct request/response */
> #define FFA_MSG_FLAG_FRAMEWORK          BIT(31, U)
> #define FFA_MSG_TYPE_MASK               0xFFU;
> -- 
> 2.34.1
>