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+# General Extensions to the GlobalPlatform TEE Internal API
+
+This document describes the OP-TEE extensions introduced with respect to the GlobalPlatform TEE API Specifications v1.0.
+
+Specific extensions documentation are part of:
+* Cryptographic Extensions
+  * [Concatenation Key Derivation](crypto_concat_kdf.md)
+  * [HMAC Key Derivation](crypto_hkdf.md)
+  * [Public-Key Key Derivation](crypto_pbkdf2.md)
+
+
+# Cache Maintenance Support
+Following functions have been introduced in order to operate with cache:
+
+    TEE_Result TEE_CacheClean(char *buf, size_t len);
+    TEE_Result TEE_CacheFlush(char *buf, size_t len);
+    TEE_Result TEE_CacheInvalidate(char *buf, size_t len);
+
+These functions are available to any Trusted Application defined with the flag TA_FLAG_CACHE_MAINTENANCE sets on. When not set, each function returns the error code TEE_ERROR_NOT_SUPPORTED.
+
+Within these extensions, a Trusted Application is able to operate on the data cache, with the following specification:
+
+Function              | Description
+:---------------------|:----------
+TEE_CacheClean()      | Write back to memory any dirty data cache lines. The line is marked as not dirty. The valid bit is unchanged
+TEE_CacheFlush()      | Purges any valid data cache lines. Any dirty cache lines                 are first written back to memory, then the cache line is invalidated.
+TEE_CacheInvalidate() | Invalidate any valid data cache lines. Any dirty line are not written back to memory.
+
+In the following 2 cases, the error code TEE_ERROR_ACCESS_DENIED is returned:
+* the memory range has not the write access, that is TEE_MEMORY_ACCESS_WRITE is not set.
+* the memory is not a User Space memory