[xen staging] optee: immediately free buffers that are released by OP-TEE

[patchbot@xxxxxxx]

commit 5b13eb1d978e9732fe2c9826b60885b687a5c4fc
Author:     Volodymyr Babchuk <Volodymyr_Babchuk@xxxxxxxx>
AuthorDate: Fri Jun 19 22:33:59 2020 +0000
Commit:     Stefano Stabellini <sstabellini@xxxxxxxxxx>
CommitDate: Wed Jul 1 10:09:38 2020 -0700

    optee: immediately free buffers that are released by OP-TEE
    
    Normal World can share a buffer with OP-TEE for two reasons:
    1. A client application wants to exchange data with TA
    2. OP-TEE asks for shared buffer for internal needs
    
    The second case was handled more strictly than necessary:
    
    1. In RPC request OP-TEE asks for buffer
    2. NW allocates buffer and provides it via RPC response
    3. Xen pins pages and translates data
    4. Xen provides buffer to OP-TEE
    5. OP-TEE uses it
    6. OP-TEE sends request to free the buffer
    7. NW frees the buffer and sends the RPC response
    8. Xen unpins pages and forgets about the buffer
    
    The problem is that Xen should forget about buffer in between stages 6
    and 7. I.e. the right flow should be like this:
    
    6. OP-TEE sends request to free the buffer
    7. Xen unpins pages and forgets about the buffer
    8. NW frees the buffer and sends the RPC response
    
    This is because OP-TEE internally frees the buffer before sending the
    "free SHM buffer" request. So we have no reason to hold reference for
    this buffer anymore. Moreover, in multiprocessor systems NW have time
    to reuse the buffer cookie for another buffer. Xen complained about this
    and denied the new buffer registration. I have seen this issue while
    running tests on iMX SoC.
    
    So, this patch basically corrects that behavior by freeing the buffer
    earlier, when handling RPC return from OP-TEE.
    
    Signed-off-by: Volodymyr Babchuk <volodymyr_babchuk@xxxxxxxx>
    Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
    Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxx>
    Release-acked-by: Paul Durrant <paul@xxxxxxx>
---
 xen/arch/arm/tee/optee.c | 32 ++++++++++++++++++++++++++++----
 1 file changed, 28 insertions(+), 4 deletions(-)

diff --git a/xen/arch/arm/tee/optee.c b/xen/arch/arm/tee/optee.c
index 6a035355db..780f37e527 100644
--- a/xen/arch/arm/tee/optee.c
+++ b/xen/arch/arm/tee/optee.c
@@ -1099,6 +1099,34 @@ static int handle_rpc_return(struct optee_domain *ctx,
         if ( shm_rpc->xen_arg->cmd == OPTEE_RPC_CMD_SHM_ALLOC )
             call->rpc_buffer_type = shm_rpc->xen_arg->params[0].u.value.a;
 
+        /*
+         * OP-TEE is signalling that it has freed the buffer that it
+         * requested before. This is the right time for us to do the
+         * same.
+         */
+        if ( shm_rpc->xen_arg->cmd == OPTEE_RPC_CMD_SHM_FREE )
+        {
+            uint64_t cookie = shm_rpc->xen_arg->params[0].u.value.b;
+
+            free_optee_shm_buf(ctx, cookie);
+
+            /*
+             * OP-TEE asks to free the buffer, but this is not the same
+             * buffer we previously allocated for it. While nothing
+             * prevents OP-TEE from asking this, it is the strange
+             * situation. This may or may not be caused by a bug in
+             * OP-TEE or mediator. But is better to print warning.
+             */
+            if ( call->rpc_data_cookie && call->rpc_data_cookie != cookie )
+            {
+                gprintk(XENLOG_ERR,
+                        "Saved RPC cookie does not corresponds to OP-TEE's 
(%"PRIx64" != %"PRIx64")\n",
+                        call->rpc_data_cookie, cookie);
+
+                WARN();
+            }
+            call->rpc_data_cookie = 0;
+        }
         unmap_domain_page(shm_rpc->xen_arg);
     }
 
@@ -1464,10 +1492,6 @@ static void handle_rpc_cmd(struct optee_domain *ctx, 
struct cpu_user_regs *regs,
             }
             break;
         case OPTEE_RPC_CMD_SHM_FREE:
-            free_optee_shm_buf(ctx, shm_rpc->xen_arg->params[0].u.value.b);
-            if ( call->rpc_data_cookie ==
-                 shm_rpc->xen_arg->params[0].u.value.b )
-                call->rpc_data_cookie = 0;
             break;
         default:
             break;
--
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