diff options
Diffstat (limited to 'Documentation/arm64')
| -rw-r--r-- | Documentation/arm64/elf_hwcaps.rst | 5 | ||||
| -rw-r--r-- | Documentation/arm64/memory-tagging-extension.rst | 26 |
2 files changed, 23 insertions, 8 deletions
diff --git a/Documentation/arm64/elf_hwcaps.rst b/Documentation/arm64/elf_hwcaps.rst index b72ff17d600a..a8f30963e550 100644 --- a/Documentation/arm64/elf_hwcaps.rst +++ b/Documentation/arm64/elf_hwcaps.rst @@ -259,6 +259,11 @@ HWCAP2_RPRES Functionality implied by ID_AA64ISAR2_EL1.RPRES == 0b0001. +HWCAP2_MTE3 + + Functionality implied by ID_AA64PFR1_EL1.MTE == 0b0011, as described + by Documentation/arm64/memory-tagging-extension.rst. + 4. Unused AT_HWCAP bits ----------------------- diff --git a/Documentation/arm64/memory-tagging-extension.rst b/Documentation/arm64/memory-tagging-extension.rst index 6ccbdc408df6..dd27f78d7608 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`` @@ -140,18 +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 --------------------- |