Re: [Xen-devel] [PATCH v2 10/13] optee: add support for RPC commands

[Julien Grall <julien.grall@xxxxxxx>]

On 10/09/18 19:14, Volodymyr Babchuk wrote:
> On 10.09.18 18:34, Julien Grall wrote:
> > On 03/09/18 17:54, Volodymyr Babchuk wrote:
> > >   static struct shm_buf *allocate_shm_buf(struct domain_ctx *ctx,
> > >                                           uint64_t cookie,
> > >                                           int pages_cnt)
> > > @@ -704,6 +732,28 @@ static bool copy_std_request_back(struct 
> > > domain_ctx *ctx,
> > >       return true;
> > >   }
> > > +static void handle_rpc_return(struct domain_ctx *ctx,
> > > +                             struct cpu_user_regs *regs,
> > > +                             struct std_call_ctx *call)
> > > +{
> > > +    call->optee_thread_id = get_user_reg(regs, 3);
> > > +    call->rpc_op = OPTEE_SMC_RETURN_GET_RPC_FUNC(get_user_reg(regs, 
> > > 0));
> > > +
> > > +    if ( call->rpc_op == OPTEE_SMC_RPC_FUNC_CMD )
> > > +    {
> > > +        /* Copy RPC request from shadowed buffer to guest */
> > > +        uint64_t cookie = get_user_reg(regs, 1) << 32 | 
> > > get_user_reg(regs, 2);
> > > +        struct shm_rpc *shm_rpc = find_shm_rpc(ctx, cookie);
> > Newline between declaration and code.
> Sorry, another habit from kernel coding style :(
I think you need to modify your habit because I am pretty sure Linux 
folks would not allow:
struct shm_rpc *rpc = find_shm(...);
if ( rpc )
  ...

The correct way is:

struct shm_rpc *rpc = find_shm(...);

if ( rpc )

Notice the newline between struct and if.

> > > +        if ( !shm_rpc )
> > > +        {
> > > +            gprintk(XENLOG_ERR, "Can't find SHM-RPC with cookie 
> > > %lx\n", cookie);
> > > +            return;
> > > +        }
> > > +        memcpy(shm_rpc->guest_arg, shm_rpc->xen_arg,
> > > +               OPTEE_MSG_GET_ARG_SIZE(shm_rpc->xen_arg->num_params));
> > > +    }
> > > +}
> > > +
> > >   static bool execute_std_call(struct domain_ctx *ctx,
> > >                                struct cpu_user_regs *regs,
> > >                                struct std_call_ctx *call)
> > > @@ -715,8 +765,7 @@ static bool execute_std_call(struct domain_ctx *ctx,
> > >       optee_ret = get_user_reg(regs, 0);
> > >       if ( OPTEE_SMC_RETURN_IS_RPC(optee_ret) )
> > >       {
> > > -        call->optee_thread_id = get_user_reg(regs, 3);
> > > -        call->rpc_op = OPTEE_SMC_RETURN_GET_RPC_FUNC(optee_ret);
> > > +        handle_rpc_return(ctx, regs, call);
> > It would make sense to introduce handle_rpc_return where you actually 
> > add those 2 lines.
> > >           return true;
> > >       }
> > > @@ -783,6 +832,74 @@ out:
> > >       return ret;
> > >   }
> > > +
> > > +static void handle_rpc_cmd_alloc(struct domain_ctx *ctx,
> > > +                                 struct cpu_user_regs *regs,
> > > +                                 struct std_call_ctx *call,
> > > +                                 struct shm_rpc *shm_rpc)
> > > +{
> > > +    if ( shm_rpc->xen_arg->params[0].attr != 
> > > (OPTEE_MSG_ATTR_TYPE_TMEM_OUTPUT |
> > > +                                            OPTEE_MSG_ATTR_NONCONTIG) )
> > > +    {
> > > +        gprintk(XENLOG_WARNING, "Invalid attrs for shared mem 
> > > buffer\n");
> > > +        return;
> > > +    }
> > > +
> > > +    /* Last entry in non_contig array is used to hold RPC-allocated 
> > > buffer */
> > > +    if ( call->non_contig[MAX_NONCONTIG_ENTRIES - 1] )
> > > +    {
> > > +        free_xenheap_pages(call->non_contig[MAX_NONCONTIG_ENTRIES - 1],
> > > + call->non_contig_order[MAX_NONCONTIG_ENTRIES - 1]);
> > > +        call->non_contig[MAX_NONCONTIG_ENTRIES - 1] = NULL;
> > > +    }
> > This is quite odd. Why don't you just deny allocating information in 
> > the non_config array? This would avoid to silently dropped any page 
> > that may have been linked together and potentially used still in use.
> No, this, actually is part of the protocol. OP-TEE can ask to allocate 
> more shared buffers, one per RPC return.
Please a give link to the spec and the paragraph.

> call->non_contig[x] is needed to hold list of pages until OP_TEE 
> consumes them. The it can be freed and reused to allocate next buffer.
> Consider this:
What is x?

> 1. OP-TEE issues RPC "allocate buffer"
> 2. NW returns list of pages
> 3. Mediator translates and stores address in non_contig[x]
> 4. OP-TEE begins to consume this list
> 5. IRQ arrives and OP-TEE forced to break the work
> 6. Mediator receives control back, but it should not free non_contig[x],
>     because it is not sure of OP-TEE finished reading from it
> 7. Xen/guest handles the IRQ and returns control back to OP-TEE
> 8. OP-TEE finishes processing this buffers and asks for another one
> 9. NW returns list of pages for the next buffer
> 10. At this point mediator is sure that OP-TEE finished processing
>      old non_contig[x], so it can free it and allocated another.
Thank you for the description of the protocol. However, it is still does 
not explain why you decided to free MAX_NONCONTIG_ENTRIES - 1. Why not 0 
or 1 or n?
Overall, it feels like to me you want to write more documentation about 
how the mediator is supposed to work.

[...]

> > Please try to avoid changing the coding style in different patch. But 
> > this one is wrong.
> Yep :( this is the artifact from splitting the big patch.
>
> > >               gprintk(XENLOG_WARNING, "Failed to allocate shm_rpc 
> > > object\n");
> > > -            ptr = 0;
> > > -        }
> > > -        else
> > > -            ptr = mfn_to_maddr(shm_rpc->guest_mfn);
> > > +            ptr = ~0;
> > Can you explain why you change from 0 to ~0?
> I had to introduce this in the original patch, actually.
What do you mean?

Cheers,

--
Julien Grall

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