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author | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-04-27 09:32:30 +0200 |
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committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2020-04-27 09:32:30 +0200 |
commit | f6402eb4a2b3192bdf23fa39ef8e85fd3691cca9 (patch) | |
tree | da8d55cd97d59cfe689fe447d98637204f2218e3 /Documentation/arm64/amu.rst | |
parent | 992a60ed0d5e312ce9a485c9e12097ac82ae4b3e (diff) | |
parent | 6a8b55ed4056ea5559ebe4f6a4b247f627870d4c (diff) | |
download | lwn-f6402eb4a2b3192bdf23fa39ef8e85fd3691cca9.tar.gz lwn-f6402eb4a2b3192bdf23fa39ef8e85fd3691cca9.zip |
Merge 5.7-rc3 into usb-next
We need the USB fixes in here too.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'Documentation/arm64/amu.rst')
-rw-r--r-- | Documentation/arm64/amu.rst | 47 |
1 files changed, 26 insertions, 21 deletions
diff --git a/Documentation/arm64/amu.rst b/Documentation/arm64/amu.rst index 5057b11100ed..036783ee327f 100644 --- a/Documentation/arm64/amu.rst +++ b/Documentation/arm64/amu.rst @@ -23,13 +23,14 @@ optional external memory-mapped interface. Version 1 of the Activity Monitors architecture implements a counter group of four fixed and architecturally defined 64-bit event counters. - - CPU cycle counter: increments at the frequency of the CPU. - - Constant counter: increments at the fixed frequency of the system - clock. - - Instructions retired: increments with every architecturally executed - instruction. - - Memory stall cycles: counts instruction dispatch stall cycles caused by - misses in the last level cache within the clock domain. + +- CPU cycle counter: increments at the frequency of the CPU. +- Constant counter: increments at the fixed frequency of the system + clock. +- Instructions retired: increments with every architecturally executed + instruction. +- Memory stall cycles: counts instruction dispatch stall cycles caused by + misses in the last level cache within the clock domain. When in WFI or WFE these counters do not increment. @@ -57,11 +58,12 @@ counters, only the presence of the extension. Firmware (code running at higher exception levels, e.g. arm-tf) support is needed to: - - Enable access for lower exception levels (EL2 and EL1) to the AMU - registers. - - Enable the counters. If not enabled these will read as 0. - - Save/restore the counters before/after the CPU is being put/brought up - from the 'off' power state. + +- Enable access for lower exception levels (EL2 and EL1) to the AMU + registers. +- Enable the counters. If not enabled these will read as 0. +- Save/restore the counters before/after the CPU is being put/brought up + from the 'off' power state. When using kernels that have this feature enabled but boot with broken firmware the user may experience panics or lockups when accessing the @@ -78,10 +80,11 @@ are not trapped in EL2/EL3. The fixed counters of AMUv1 are accessible though the following system register definitions: - - SYS_AMEVCNTR0_CORE_EL0 - - SYS_AMEVCNTR0_CONST_EL0 - - SYS_AMEVCNTR0_INST_RET_EL0 - - SYS_AMEVCNTR0_MEM_STALL_EL0 + +- SYS_AMEVCNTR0_CORE_EL0 +- SYS_AMEVCNTR0_CONST_EL0 +- SYS_AMEVCNTR0_INST_RET_EL0 +- SYS_AMEVCNTR0_MEM_STALL_EL0 Auxiliary platform specific counters can be accessed using SYS_AMEVCNTR1_EL0(n), where n is a value between 0 and 15. @@ -93,9 +96,10 @@ Userspace access ---------------- Currently, access from userspace to the AMU registers is disabled due to: - - Security reasons: they might expose information about code executed in - secure mode. - - Purpose: AMU counters are intended for system management use. + +- Security reasons: they might expose information about code executed in + secure mode. +- Purpose: AMU counters are intended for system management use. Also, the presence of the feature is not visible to userspace. @@ -105,8 +109,9 @@ Virtualization Currently, access from userspace (EL0) and kernelspace (EL1) on the KVM guest side is disabled due to: - - Security reasons: they might expose information about code executed - by other guests or the host. + +- Security reasons: they might expose information about code executed + by other guests or the host. Any attempt to access the AMU registers will result in an UNDEFINED exception being injected into the guest. |