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Diffstat (limited to '')
| -rw-r--r-- | Documentation/arm64/memory-tagging-extension.rst | 54 |
1 files changed, 44 insertions, 10 deletions
diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documentation/arm64/memory-tagging-extension.rst index 7b99c8f428eb..dbae47bba25e 100644 --- a/Documentation/arm64/memory-tagging-extension.rst +++ b/Documentation/arm64/memory-tagging-extension.rst @@ -76,6 +76,9 @@ configurable behaviours: with ``.si_code = SEGV_MTEAERR`` and ``.si_addr = 0`` (the faulting address is unknown). +- *Asymmetric* - Reads are handled as for synchronous mode while writes + are handled as for asynchronous mode. + The user can select the above modes, per thread, using the ``prctl(PR_SET_TAGGED_ADDR_CTRL, flags, 0, 0, 0)`` system call where ``flags`` contains any number of the following values in the ``PR_MTE_TCF_MASK`` @@ -91,8 +94,9 @@ mode is specified, the program will run in that mode. If multiple modes are specified, the mode is selected as described in the "Per-CPU preferred tag checking modes" section below. -The current tag check fault mode can be read using the -``prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0)`` system call. +The current tag check fault configuration can be read using the +``prctl(PR_GET_TAGGED_ADDR_CTRL, 0, 0, 0, 0)`` system call. If +multiple modes were requested then all will be reported. Tag checking can also be disabled for a user thread by setting the ``PSTATE.TCO`` bit with ``MSR TCO, #1``. @@ -139,18 +143,25 @@ tag checking mode as the CPU's preferred tag checking mode. The preferred tag checking mode for each CPU is controlled by ``/sys/devices/system/cpu/cpu<N>/mte_tcf_preferred``, to which a -privileged user may write the value ``async`` or ``sync``. The default -preferred mode for each CPU is ``async``. +privileged user may write the value ``async``, ``sync`` or ``asymm``. The +default preferred mode for each CPU is ``async``. To allow a program to potentially run in the CPU's preferred tag checking mode, the user program may set multiple tag check fault mode bits in the ``flags`` argument to the ``prctl(PR_SET_TAGGED_ADDR_CTRL, -flags, 0, 0, 0)`` system call. If the CPU's preferred tag checking -mode is in the task's set of provided tag checking modes (this will -always be the case at present because the kernel only supports two -tag checking modes, but future kernels may support more modes), that -mode will be selected. Otherwise, one of the modes in the task's mode -set will be selected in a currently unspecified manner. +flags, 0, 0, 0)`` system call. If both synchronous and asynchronous +modes are requested then asymmetric mode may also be selected by the +kernel. If the CPU's preferred tag checking mode is in the task's set +of provided tag checking modes, that mode will be selected. Otherwise, +one of the modes in the task's mode will be selected by the kernel +from the task's mode set using the preference order: + + 1. Asynchronous + 2. Asymmetric + 3. Synchronous + +Note that there is no way for userspace to request multiple modes and +also disable asymmetric mode. Initial process state --------------------- @@ -213,6 +224,29 @@ address ABI control and MTE configuration of a process as per the Documentation/arm64/tagged-address-abi.rst and above. The corresponding ``regset`` is 1 element of 8 bytes (``sizeof(long))``). +Core dump support +----------------- + +The allocation tags for user memory mapped with ``PROT_MTE`` are dumped +in the core file as additional ``PT_AARCH64_MEMTAG_MTE`` segments. The +program header for such segment is defined as: + +:``p_type``: ``PT_AARCH64_MEMTAG_MTE`` +:``p_flags``: 0 +:``p_offset``: segment file offset +:``p_vaddr``: segment virtual address, same as the corresponding + ``PT_LOAD`` segment +:``p_paddr``: 0 +:``p_filesz``: segment size in file, calculated as ``p_mem_sz / 32`` + (two 4-bit tags cover 32 bytes of memory) +:``p_memsz``: segment size in memory, same as the corresponding + ``PT_LOAD`` segment +:``p_align``: 0 + +The tags are stored in the core file at ``p_offset`` as two 4-bit tags +in a byte. With the tag granule of 16 bytes, a 4K page requires 128 +bytes in the core file. + Example of correct usage ======================== |