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

[Jens Wiklander <jens.wiklander@xxxxxxxxxx>]

Hi Bertrand,

On Thu, Mar 2, 2023 at 4:05 PM Bertrand Marquis
<Bertrand.Marquis@xxxxxxx> wrote:
>
> 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.

Yes, I'll remove it.

>
> > /* 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 ?

The SMC Calling Convention says:
When an SMC32/HVC32 call is made from AArch64:
- A Function Identifier is passed in register W0.
- Arguments are passed in registers W1-W7.

So masking off the higher bits is all that should be done.

>
> > +
> > +    /* 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.

I'll add an arbitrary upper limit and a print if it's exceeded.

>
>
> > +
> > +    /* 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.

OK

Cheers,
Jens

>
>
> 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
> >
>