Re: [XEN PATCH v7 10/20] xen/arm: ffa: add direct request support

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jens,

> On 22 Feb 2023, at 16:33, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> 
> Adds support for sending a FF-A direct request. Checks that the SP also
> supports handling a 32-bit direct request. 64-bit direct requests are
> not used by the mediator itself so there is not need to check for that.
> 
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
> xen/arch/arm/tee/ffa.c | 119 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 119 insertions(+)
> 
> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> index 463fd7730573..a5d8a12635b6 100644
> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -142,6 +142,7 @@
> 
> struct ffa_ctx {
>     uint32_t guest_vers;
> +    bool interrupted;

This is added and set here for one special error code but is never used.
I would suggest to introduce this when there will be an action based on it.

> };
> 
> /* Negotiated FF-A version to use with the SPMC */
> @@ -167,6 +168,55 @@ static bool ffa_get_version(uint32_t *vers)
>     return true;
> }
> 
> +static int32_t get_ffa_ret_code(const struct arm_smccc_1_2_regs *resp)
> +{
> +    switch ( resp->a0 )
> +    {
> +    case FFA_ERROR:
> +        if ( resp->a2 )
> +            return resp->a2;
> +        else
> +            return FFA_RET_NOT_SUPPORTED;
> +    case FFA_SUCCESS_32:
> +    case FFA_SUCCESS_64:
> +        return FFA_RET_OK;
> +    default:
> +        return FFA_RET_NOT_SUPPORTED;
> +    }
> +}
> +
> +static int32_t ffa_simple_call(uint32_t fid, register_t a1, register_t a2,
> +                               register_t a3, register_t a4)
> +{
> +    const struct arm_smccc_1_2_regs arg = {
> +        .a0 = fid,
> +        .a1 = a1,
> +        .a2 = a2,
> +        .a3 = a3,
> +        .a4 = a4,
> +    };
> +    struct arm_smccc_1_2_regs resp;
> +
> +    arm_smccc_1_2_smc(&arg, &resp);
> +
> +    return get_ffa_ret_code(&resp);
> +}
> +
> +static int32_t ffa_features(uint32_t id)
> +{
> +    return ffa_simple_call(FFA_FEATURES, id, 0, 0, 0);
> +}
> +
> +static bool check_mandatory_feature(uint32_t id)
> +{
> +    uint32_t ret = ffa_features(id);
> +
> +    if (ret)
> +        printk(XENLOG_ERR "ffa: mandatory feature id %#x missing\n", id);

It might be useful here to actually print the error code.
Are we sure that all errors actually mean not supported ?

> +
> +    return !ret;
> +}
> +
> static uint16_t get_vm_id(const struct domain *d)
> {
>     /* +1 since 0 is reserved for the hypervisor in FF-A */
> @@ -208,6 +258,66 @@ static void handle_version(struct cpu_user_regs *regs)
>     set_regs(regs, vers, 0, 0, 0, 0, 0, 0, 0);
> }
> 
> +static void handle_msg_send_direct_req(struct cpu_user_regs *regs, uint32_t 
> fid)
> +{
> +    struct arm_smccc_1_2_regs arg = { .a0 = fid, };
> +    struct arm_smccc_1_2_regs resp = { };
> +    struct domain *d = current->domain;
> +    struct ffa_ctx *ctx = d->arch.tee;
> +    uint32_t src_dst;
> +    uint64_t mask;
> +
> +    if ( smccc_is_conv_64(fid) )
> +        mask = GENMASK_ULL(63, 0);
> +    else
> +        mask = GENMASK_ULL(31, 0);
> +
> +    src_dst = get_user_reg(regs, 1);
> +    if ( (src_dst >> 16) != get_vm_id(d) )
> +    {
> +        resp.a0 = FFA_ERROR;
> +        resp.a2 = FFA_RET_INVALID_PARAMETERS;
> +        goto out;
> +    }
> +
> +    arg.a1 = src_dst;
> +    arg.a2 = get_user_reg(regs, 2) & mask;
> +    arg.a3 = get_user_reg(regs, 3) & mask;
> +    arg.a4 = get_user_reg(regs, 4) & mask;
> +    arg.a5 = get_user_reg(regs, 5) & mask;
> +    arg.a6 = get_user_reg(regs, 6) & mask;
> +    arg.a7 = get_user_reg(regs, 7) & mask;
> +
> +    while ( true )
> +    {
> +        arm_smccc_1_2_smc(&arg, &resp);
> +
> +        switch ( resp.a0 )
> +        {
> +        case FFA_INTERRUPT:
> +            ctx->interrupted = true;
> +            goto out;
> +        case FFA_ERROR:
> +        case FFA_SUCCESS_32:
> +        case FFA_SUCCESS_64:
> +        case FFA_MSG_SEND_DIRECT_RESP_32:
> +        case FFA_MSG_SEND_DIRECT_RESP_64:
> +            goto out;
> +        default:
> +            /* Bad fid, report back. */
> +            memset(&arg, 0, sizeof(arg));
> +            arg.a0 = FFA_ERROR;
> +            arg.a1 = src_dst;
> +            arg.a2 = FFA_RET_NOT_SUPPORTED;
> +            continue;

There is a potential infinite loop here and i do not understand
why this needs to be done.
Here if something is returning a value that you do not understand
you send back an ERROR to it. I do not find in the spec where this
is supposed to be done.
Can you explain a bit here ?

> +        }
> +    }
> +
> +out:
> +    set_regs(regs, resp.a0, resp.a1 & mask, resp.a2 & mask, resp.a3 & mask,
> +             resp.a4 & mask, resp.a5 & mask, resp.a6 & mask, resp.a7 & mask);
> +}
> +
> static bool ffa_handle_call(struct cpu_user_regs *regs)
> {
>     uint32_t fid = get_user_reg(regs, 0);
> @@ -225,6 +335,12 @@ static bool ffa_handle_call(struct cpu_user_regs *regs)
>     case FFA_ID_GET:
>         set_regs_success(regs, get_vm_id(d), 0);
>         return true;
> +    case FFA_MSG_SEND_DIRECT_REQ_32:
> +#ifdef CONFIG_ARM_64
> +    case FFA_MSG_SEND_DIRECT_REQ_64:
> +#endif
> +        handle_msg_send_direct_req(regs, fid);
> +        return true;
> 
>     default:
>         gprintk(XENLOG_ERR, "ffa: unhandled fid 0x%x\n", fid);
> @@ -310,6 +426,9 @@ static bool ffa_probe(void)
>     printk(XENLOG_INFO "ARM FF-A Firmware version %u.%u\n",
>            major_vers, minor_vers);
> 
> +    if ( !check_mandatory_feature(FFA_MSG_SEND_DIRECT_REQ_32) )
> +        return false;

One could not need this feature and here this will make everything unavailable 
instead.
Why not just reporting back the unsupported error to clients using unsupported 
interfaces ?

Cheers
Bertrand

> +
>     ffa_version = vers;
> 
>     return true;
> -- 
> 2.34.1
>