diff options
Diffstat (limited to 'Documentation/arch/powerpc')
| -rw-r--r-- | Documentation/arch/powerpc/dexcr.rst | 141 | ||||
| -rw-r--r-- | Documentation/arch/powerpc/firmware-assisted-dump.rst | 91 | ||||
| -rw-r--r-- | Documentation/arch/powerpc/kvm-nested.rst | 4 |
3 files changed, 184 insertions, 52 deletions
diff --git a/Documentation/arch/powerpc/dexcr.rst b/Documentation/arch/powerpc/dexcr.rst index 615a631f51..ab0724212f 100644 --- a/Documentation/arch/powerpc/dexcr.rst +++ b/Documentation/arch/powerpc/dexcr.rst @@ -36,8 +36,145 @@ state for a process. Configuration ============= -The DEXCR is currently unconfigurable. All threads are run with the -NPHIE aspect enabled. +prctl +----- + +A process can control its own userspace DEXCR value using the +``PR_PPC_GET_DEXCR`` and ``PR_PPC_SET_DEXCR`` pair of +:manpage:`prctl(2)` commands. These calls have the form:: + + prctl(PR_PPC_GET_DEXCR, unsigned long which, 0, 0, 0); + prctl(PR_PPC_SET_DEXCR, unsigned long which, unsigned long ctrl, 0, 0); + +The possible 'which' and 'ctrl' values are as follows. Note there is no relation +between the 'which' value and the DEXCR aspect's index. + +.. flat-table:: + :header-rows: 1 + :widths: 2 7 1 + + * - ``prctl()`` which + - Aspect name + - Aspect index + + * - ``PR_PPC_DEXCR_SBHE`` + - Speculative Branch Hint Enable (SBHE) + - 0 + + * - ``PR_PPC_DEXCR_IBRTPD`` + - Indirect Branch Recurrent Target Prediction Disable (IBRTPD) + - 3 + + * - ``PR_PPC_DEXCR_SRAPD`` + - Subroutine Return Address Prediction Disable (SRAPD) + - 4 + + * - ``PR_PPC_DEXCR_NPHIE`` + - Non-Privileged Hash Instruction Enable (NPHIE) + - 5 + +.. flat-table:: + :header-rows: 1 + :widths: 2 8 + + * - ``prctl()`` ctrl + - Meaning + + * - ``PR_PPC_DEXCR_CTRL_EDITABLE`` + - This aspect can be configured with PR_PPC_SET_DEXCR (get only) + + * - ``PR_PPC_DEXCR_CTRL_SET`` + - This aspect is set / set this aspect + + * - ``PR_PPC_DEXCR_CTRL_CLEAR`` + - This aspect is clear / clear this aspect + + * - ``PR_PPC_DEXCR_CTRL_SET_ONEXEC`` + - This aspect will be set after exec / set this aspect after exec + + * - ``PR_PPC_DEXCR_CTRL_CLEAR_ONEXEC`` + - This aspect will be clear after exec / clear this aspect after exec + +Note that + +* which is a plain value, not a bitmask. Aspects must be worked with individually. + +* ctrl is a bitmask. ``PR_PPC_GET_DEXCR`` returns both the current and onexec + configuration. For example, ``PR_PPC_GET_DEXCR`` may return + ``PR_PPC_DEXCR_CTRL_EDITABLE | PR_PPC_DEXCR_CTRL_SET | + PR_PPC_DEXCR_CTRL_CLEAR_ONEXEC``. This would indicate the aspect is currently + set, it will be cleared when you run exec, and you can change this with the + ``PR_PPC_SET_DEXCR`` prctl. + +* The set/clear terminology refers to setting/clearing the bit in the DEXCR. + For example:: + + prctl(PR_PPC_SET_DEXCR, PR_PPC_DEXCR_IBRTPD, PR_PPC_DEXCR_CTRL_SET, 0, 0); + + will set the IBRTPD aspect bit in the DEXCR, causing indirect branch prediction + to be disabled. + +* The status returned by ``PR_PPC_GET_DEXCR`` represents what value the process + would like applied. It does not include any alternative overrides, such as if + the hypervisor is enforcing the aspect be set. To see the true DEXCR state + software should read the appropriate SPRs directly. + +* The aspect state when starting a process is copied from the parent's state on + :manpage:`fork(2)`. The state is reset to a fixed value on + :manpage:`execve(2)`. The PR_PPC_SET_DEXCR prctl() can control both of these + values. + +* The ``*_ONEXEC`` controls do not change the current process's DEXCR. + +Use ``PR_PPC_SET_DEXCR`` with one of ``PR_PPC_DEXCR_CTRL_SET`` or +``PR_PPC_DEXCR_CTRL_CLEAR`` to edit a given aspect. + +Common error codes for both getting and setting the DEXCR are as follows: + +.. flat-table:: + :header-rows: 1 + :widths: 2 8 + + * - Error + - Meaning + + * - ``EINVAL`` + - The DEXCR is not supported by the kernel. + + * - ``ENODEV`` + - The aspect is not recognised by the kernel or not supported by the + hardware. + +``PR_PPC_SET_DEXCR`` may also report the following error codes: + +.. flat-table:: + :header-rows: 1 + :widths: 2 8 + + * - Error + - Meaning + + * - ``EINVAL`` + - The ctrl value contains unrecognised flags. + + * - ``EINVAL`` + - The ctrl value contains mutually conflicting flags (e.g., + ``PR_PPC_DEXCR_CTRL_SET | PR_PPC_DEXCR_CTRL_CLEAR``) + + * - ``EPERM`` + - This aspect cannot be modified with prctl() (check for the + PR_PPC_DEXCR_CTRL_EDITABLE flag with PR_PPC_GET_DEXCR). + + * - ``EPERM`` + - The process does not have sufficient privilege to perform the operation. + For example, clearing NPHIE on exec is a privileged operation (a process + can still clear its own NPHIE aspect without privileges). + +This interface allows a process to control its own DEXCR aspects, and also set +the initial DEXCR value for any children in its process tree (up to the next +child to use an ``*_ONEXEC`` control). This allows fine-grained control over the +default value of the DEXCR, for example allowing containers to run with different +default values. coredump and ptrace diff --git a/Documentation/arch/powerpc/firmware-assisted-dump.rst b/Documentation/arch/powerpc/firmware-assisted-dump.rst index e363fc4852..7e37aadd1f 100644 --- a/Documentation/arch/powerpc/firmware-assisted-dump.rst +++ b/Documentation/arch/powerpc/firmware-assisted-dump.rst @@ -134,12 +134,12 @@ that are run. If there is dump data, then the memory is held. If there is no waiting dump data, then only the memory required to -hold CPU state, HPTE region, boot memory dump, FADump header and -elfcore header, is usually reserved at an offset greater than boot -memory size (see Fig. 1). This area is *not* released: this region -will be kept permanently reserved, so that it can act as a receptacle -for a copy of the boot memory content in addition to CPU state and -HPTE region, in the case a crash does occur. +hold CPU state, HPTE region, boot memory dump, and FADump header is +usually reserved at an offset greater than boot memory size (see Fig. 1). +This area is *not* released: this region will be kept permanently +reserved, so that it can act as a receptacle for a copy of the boot +memory content in addition to CPU state and HPTE region, in the case +a crash does occur. Since this reserved memory area is used only after the system crash, there is no point in blocking this significant chunk of memory from @@ -153,22 +153,22 @@ that were present in CMA region:: o Memory Reservation during first kernel - Low memory Top of memory - 0 boot memory size |<--- Reserved dump area --->| | - | | | Permanent Reservation | | - V V | | V - +-----------+-----/ /---+---+----+-------+-----+-----+----+--+ - | | |///|////| DUMP | HDR | ELF |////| | - +-----------+-----/ /---+---+----+-------+-----+-----+----+--+ - | ^ ^ ^ ^ ^ - | | | | | | - \ CPU HPTE / | | - ------------------------------ | | - Boot memory content gets transferred | | - to reserved area by firmware at the | | - time of crash. | | - FADump Header | - (meta area) | + Low memory Top of memory + 0 boot memory size |<------ Reserved dump area ----->| | + | | | Permanent Reservation | | + V V | | V + +-----------+-----/ /---+---+----+-----------+-------+----+-----+ + | | |///|////| DUMP | HDR |////| | + +-----------+-----/ /---+---+----+-----------+-------+----+-----+ + | ^ ^ ^ ^ ^ + | | | | | | + \ CPU HPTE / | | + -------------------------------- | | + Boot memory content gets transferred | | + to reserved area by firmware at the | | + time of crash. | | + FADump Header | + (meta area) | | | Metadata: This area holds a metadata structure whose @@ -186,13 +186,20 @@ that were present in CMA region:: 0 boot memory size | | |<------------ Crash preserved area ------------>| V V |<--- Reserved dump area --->| | - +-----------+-----/ /---+---+----+-------+-----+-----+----+--+ - | | |///|////| DUMP | HDR | ELF |////| | - +-----------+-----/ /---+---+----+-------+-----+-----+----+--+ - | | - V V - Used by second /proc/vmcore - kernel to boot + +----+---+--+-----/ /---+---+----+-------+-----+-----+-------+ + | |ELF| | |///|////| DUMP | HDR |/////| | + +----+---+--+-----/ /---+---+----+-------+-----+-----+-------+ + | | | | | | + ----- ------------------------------ --------------- + \ | | + \ | | + \ | | + \ | ---------------------------- + \ | / + \ | / + \ | / + /proc/vmcore + +---+ |///| -> Regions (CPU, HPTE & Metadata) marked like this in the above @@ -200,6 +207,12 @@ that were present in CMA region:: does not have CPU & HPTE regions while Metadata region is not supported on pSeries currently. + +---+ + |ELF| -> elfcorehdr, it is created in second kernel after crash. + +---+ + + Note: Memory from 0 to the boot memory size is used by second kernel + Fig. 2 @@ -353,26 +366,6 @@ TODO: - Need to come up with the better approach to find out more accurate boot memory size that is required for a kernel to boot successfully when booted with restricted memory. - - The FADump implementation introduces a FADump crash info structure - in the scratch area before the ELF core header. The idea of introducing - this structure is to pass some important crash info data to the second - kernel which will help second kernel to populate ELF core header with - correct data before it gets exported through /proc/vmcore. The current - design implementation does not address a possibility of introducing - additional fields (in future) to this structure without affecting - compatibility. Need to come up with the better approach to address this. - - The possible approaches are: - - 1. Introduce version field for version tracking, bump up the version - whenever a new field is added to the structure in future. The version - field can be used to find out what fields are valid for the current - version of the structure. - 2. Reserve the area of predefined size (say PAGE_SIZE) for this - structure and have unused area as reserved (initialized to zero) - for future field additions. - - The advantage of approach 1 over 2 is we don't need to reserve extra space. Author: Mahesh Salgaonkar <mahesh@linux.vnet.ibm.com> diff --git a/Documentation/arch/powerpc/kvm-nested.rst b/Documentation/arch/powerpc/kvm-nested.rst index 630602a8aa..5defd13cc6 100644 --- a/Documentation/arch/powerpc/kvm-nested.rst +++ b/Documentation/arch/powerpc/kvm-nested.rst @@ -546,7 +546,9 @@ table information. +--------+-------+----+--------+----------------------------------+ | 0x1052 | 0x08 | RW | T | CTRL | +--------+-------+----+--------+----------------------------------+ -| 0x1053-| | | | Reserved | +| 0x1053 | 0x08 | RW | T | DPDES | ++--------+-------+----+--------+----------------------------------+ +| 0x1054-| | | | Reserved | | 0x1FFF | | | | | +--------+-------+----+--------+----------------------------------+ | 0x2000 | 0x04 | RW | T | CR | |