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-rw-r--r--Documentation/arm64/tagged-address-abi.rst11
1 files changed, 9 insertions, 2 deletions
diff --git a/Documentation/arm64/tagged-address-abi.rst b/Documentation/arm64/tagged-address-abi.rst
index d4a85d535bf9..4a9d9c794ee5 100644
--- a/Documentation/arm64/tagged-address-abi.rst
+++ b/Documentation/arm64/tagged-address-abi.rst
@@ -44,8 +44,15 @@ The AArch64 Tagged Address ABI has two stages of relaxation depending
how the user addresses are used by the kernel:
1. User addresses not accessed by the kernel but used for address space
- management (e.g. ``mmap()``, ``mprotect()``, ``madvise()``). The use
- of valid tagged pointers in this context is always allowed.
+ management (e.g. ``mprotect()``, ``madvise()``). The use of valid
+ tagged pointers in this context is allowed with the exception of
+ ``brk()``, ``mmap()`` and the ``new_address`` argument to
+ ``mremap()`` as these have the potential to alias with existing
+ user addresses.
+
+ NOTE: This behaviour changed in v5.6 and so some earlier kernels may
+ incorrectly accept valid tagged pointers for the ``brk()``,
+ ``mmap()`` and ``mremap()`` system calls.
2. User addresses accessed by the kernel (e.g. ``write()``). This ABI
relaxation is disabled by default and the application thread needs to