Re: [XEN PATCH v7 13/20] xen/arm: ffa: support mapping guest RX/TX buffers

[Bertrand Marquis <Bertrand.Marquis@xxxxxxx>]

Hi Jens,

> On 22 Feb 2023, at 16:33, Jens Wiklander <jens.wiklander@xxxxxxxxxx> wrote:
> 
> Adds support in the mediator to map and unmap the RX and TX buffers
> provided by the guest using the two FF-A functions FFA_RXTX_MAP and
> FFA_RXTX_UNMAP.
> 
> These buffer are later used to to transmit data that cannot be passed in
> registers only.
> 
> Signed-off-by: Jens Wiklander <jens.wiklander@xxxxxxxxxx>
> ---
> xen/arch/arm/tee/ffa.c | 127 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 127 insertions(+)
> 
> diff --git a/xen/arch/arm/tee/ffa.c b/xen/arch/arm/tee/ffa.c
> index f1b014b6c7f4..953b6dfd5eca 100644
> --- a/xen/arch/arm/tee/ffa.c
> +++ b/xen/arch/arm/tee/ffa.c
> @@ -149,10 +149,17 @@ struct ffa_partition_info_1_1 {
> };
> 
> struct ffa_ctx {
> +    void *rx;
> +    const void *tx;
> +    struct page_info *rx_pg;
> +    struct page_info *tx_pg;
> +    unsigned int page_count;
>     uint32_t guest_vers;
> +    bool tx_is_mine;
>     bool interrupted;
> };
> 
> +
Newline probably added by mistake.

> /* Negotiated FF-A version to use with the SPMC */
> static uint32_t ffa_version __ro_after_init;
> 
> @@ -337,6 +344,11 @@ static void set_regs(struct cpu_user_regs *regs, 
> register_t v0, register_t v1,
>         set_user_reg(regs, 7, v7);
> }
> 
> +static void set_regs_error(struct cpu_user_regs *regs, uint32_t error_code)
> +{
> +    set_regs(regs, FFA_ERROR, 0, error_code, 0, 0, 0, 0, 0);
> +}
> +
> static void set_regs_success(struct cpu_user_regs *regs, uint32_t w2,
>                              uint32_t w3)
> {
> @@ -358,6 +370,99 @@ static void handle_version(struct cpu_user_regs *regs)
>     set_regs(regs, vers, 0, 0, 0, 0, 0, 0, 0);
> }
> 
> +static uint32_t handle_rxtx_map(uint32_t fid, register_t tx_addr,
> +                                register_t rx_addr, uint32_t page_count)
> +{
> +    uint32_t ret = FFA_RET_INVALID_PARAMETERS;
> +    struct domain *d = current->domain;
> +    struct ffa_ctx *ctx = d->arch.tee;
> +    struct page_info *tx_pg;
> +    struct page_info *rx_pg;
> +    p2m_type_t t;
> +    void *rx;
> +    void *tx;
> +
> +    if ( !smccc_is_conv_64(fid) )
> +    {
> +        tx_addr &= UINT32_MAX;
> +        rx_addr &= UINT32_MAX;
> +    }

I am bit wondering here what we should do:
- we could just say that 32bit version of the call is not allowed for non 32bit 
guests
- we could check that the highest bits are 0 for 64bit guests and return an 
error if not
- we can just mask hopping that if there was a mistake the address after the 
mask
does not exist in the guest space

At the end nothing in the spec is preventing a 64bit guest to use the 32bit so 
it might
be a good idea to return an error if the highest 32bit are not 0 here ?

> +
> +    /* For now to keep things simple, only deal with a single page */
> +    if ( page_count != 1 )
> +        return FFA_RET_NOT_SUPPORTED;

Please add a TODO here and a print as this is a limitation we will probably 
have to
work on soon.


> +
> +    /* Already mapped */
> +    if ( ctx->rx )
> +        return FFA_RET_DENIED;
> +
> +    tx_pg = get_page_from_gfn(d, gfn_x(gaddr_to_gfn(tx_addr)), &t, 
> P2M_ALLOC);
> +    if ( !tx_pg )
> +        return FFA_RET_INVALID_PARAMETERS;
> +    /* Only normal RAM for now */
> +    if ( !p2m_is_ram(t) )
> +        goto err_put_tx_pg;
> +
> +    rx_pg = get_page_from_gfn(d, gfn_x(gaddr_to_gfn(rx_addr)), &t, 
> P2M_ALLOC);
> +    if ( !tx_pg )
> +        goto err_put_tx_pg;
> +    /* Only normal RAM for now */
> +    if ( !p2m_is_ram(t) )
> +        goto err_put_rx_pg;
> +
> +    tx = __map_domain_page_global(tx_pg);
> +    if ( !tx )
> +        goto err_put_rx_pg;
> +
> +    rx = __map_domain_page_global(rx_pg);
> +    if ( !rx )
> +        goto err_unmap_tx;
> +
> +    ctx->rx = rx;
> +    ctx->tx = tx;
> +    ctx->rx_pg = rx_pg;
> +    ctx->tx_pg = tx_pg;
> +    ctx->page_count = 1;

please use page_count here instead of 1 so that this is not forgotten once
we add support for more pages.


Cheers
Bertrand

> +    ctx->tx_is_mine = true;
> +    return FFA_RET_OK;
> +
> +err_unmap_tx:
> +    unmap_domain_page_global(tx);
> +err_put_rx_pg:
> +    put_page(rx_pg);
> +err_put_tx_pg:
> +    put_page(tx_pg);
> +
> +    return ret;
> +}
> +
> +static void rxtx_unmap(struct ffa_ctx *ctx)
> +{
> +    unmap_domain_page_global(ctx->rx);
> +    unmap_domain_page_global(ctx->tx);
> +    put_page(ctx->rx_pg);
> +    put_page(ctx->tx_pg);
> +    ctx->rx = NULL;
> +    ctx->tx = NULL;
> +    ctx->rx_pg = NULL;
> +    ctx->tx_pg = NULL;
> +    ctx->page_count = 0;
> +    ctx->tx_is_mine = false;
> +}
> +
> +static uint32_t handle_rxtx_unmap(void)
> +{
> +    struct domain *d = current->domain;
> +    struct ffa_ctx *ctx = d->arch.tee;
> +
> +    if ( !ctx->rx )
> +        return FFA_RET_INVALID_PARAMETERS;
> +
> +    rxtx_unmap(ctx);
> +
> +    return FFA_RET_OK;
> +}
> +
> static void handle_msg_send_direct_req(struct cpu_user_regs *regs, uint32_t 
> fid)
> {
>     struct arm_smccc_1_2_regs arg = { .a0 = fid, };
> @@ -423,6 +528,7 @@ static bool ffa_handle_call(struct cpu_user_regs *regs)
>     uint32_t fid = get_user_reg(regs, 0);
>     struct domain *d = current->domain;
>     struct ffa_ctx *ctx = d->arch.tee;
> +    int e;
> 
>     if ( !ctx )
>         return false;
> @@ -435,6 +541,24 @@ 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_RXTX_MAP_32:
> +#ifdef CONFIG_ARM_64
> +    case FFA_RXTX_MAP_64:
> +#endif
> +        e = handle_rxtx_map(fid, get_user_reg(regs, 1), get_user_reg(regs, 
> 2),
> +                            get_user_reg(regs, 3));
> +        if ( e )
> +            set_regs_error(regs, e);
> +        else
> +            set_regs_success(regs, 0, 0);
> +        return true;
> +    case FFA_RXTX_UNMAP:
> +        e = handle_rxtx_unmap();
> +        if ( e )
> +            set_regs_error(regs, e);
> +        else
> +            set_regs_success(regs, 0, 0);
> +        return true;
>     case FFA_MSG_SEND_DIRECT_REQ_32:
> #ifdef CONFIG_ARM_64
>     case FFA_MSG_SEND_DIRECT_REQ_64:
> @@ -515,6 +639,9 @@ static int ffa_relinquish_resources(struct domain *d)
>                    get_vm_id(d), subscr_vm_destroyed[n], res);
>     }
> 
> +    if ( ctx->rx )
> +        rxtx_unmap(ctx);
> +
>     XFREE(d->arch.tee);
> 
>     return 0;
> -- 
> 2.34.1
>