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Documentation: arm64: fix amu.rst doc warnings
Fix bullet list formatting to eliminate doc warnings: Documentation/arm64/amu.rst:26: WARNING: Unexpected indentation. Documentation/arm64/amu.rst:60: WARNING: Unexpected indentation. Documentation/arm64/amu.rst:81: WARNING: Unexpected indentation. Documentation/arm64/amu.rst:108: WARNING: Unexpected indentation. Signed-off-by: Randy Dunlap <rdunlap@infradead.org> Cc: Ionela Voinescu <ionela.voinescu@arm.com> Cc: Will Deacon <will@kernel.org> Cc: linux-arm-kernel@lists.infradead.org Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
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@ -23,13 +23,14 @@ optional external memory-mapped interface.
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Version 1 of the Activity Monitors architecture implements a counter group
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of four fixed and architecturally defined 64-bit event counters.
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- CPU cycle counter: increments at the frequency of the CPU.
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- Constant counter: increments at the fixed frequency of the system
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clock.
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- Instructions retired: increments with every architecturally executed
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instruction.
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- Memory stall cycles: counts instruction dispatch stall cycles caused by
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misses in the last level cache within the clock domain.
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- CPU cycle counter: increments at the frequency of the CPU.
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- Constant counter: increments at the fixed frequency of the system
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clock.
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- Instructions retired: increments with every architecturally executed
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instruction.
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- Memory stall cycles: counts instruction dispatch stall cycles caused by
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misses in the last level cache within the clock domain.
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When in WFI or WFE these counters do not increment.
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@ -57,11 +58,12 @@ counters, only the presence of the extension.
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Firmware (code running at higher exception levels, e.g. arm-tf) support is
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needed to:
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- Enable access for lower exception levels (EL2 and EL1) to the AMU
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registers.
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- Enable the counters. If not enabled these will read as 0.
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- Save/restore the counters before/after the CPU is being put/brought up
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from the 'off' power state.
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- Enable access for lower exception levels (EL2 and EL1) to the AMU
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registers.
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- Enable the counters. If not enabled these will read as 0.
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- Save/restore the counters before/after the CPU is being put/brought up
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from the 'off' power state.
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When using kernels that have this feature enabled but boot with broken
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firmware the user may experience panics or lockups when accessing the
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@ -78,10 +80,11 @@ are not trapped in EL2/EL3.
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The fixed counters of AMUv1 are accessible though the following system
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register definitions:
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- SYS_AMEVCNTR0_CORE_EL0
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- SYS_AMEVCNTR0_CONST_EL0
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- SYS_AMEVCNTR0_INST_RET_EL0
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- SYS_AMEVCNTR0_MEM_STALL_EL0
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- SYS_AMEVCNTR0_CORE_EL0
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- SYS_AMEVCNTR0_CONST_EL0
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- SYS_AMEVCNTR0_INST_RET_EL0
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- SYS_AMEVCNTR0_MEM_STALL_EL0
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Auxiliary platform specific counters can be accessed using
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SYS_AMEVCNTR1_EL0(n), where n is a value between 0 and 15.
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@ -93,9 +96,10 @@ Userspace access
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----------------
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Currently, access from userspace to the AMU registers is disabled due to:
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- Security reasons: they might expose information about code executed in
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secure mode.
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- Purpose: AMU counters are intended for system management use.
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- Security reasons: they might expose information about code executed in
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secure mode.
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- Purpose: AMU counters are intended for system management use.
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Also, the presence of the feature is not visible to userspace.
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@ -105,8 +109,9 @@ Virtualization
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Currently, access from userspace (EL0) and kernelspace (EL1) on the KVM
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guest side is disabled due to:
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- Security reasons: they might expose information about code executed
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by other guests or the host.
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- Security reasons: they might expose information about code executed
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by other guests or the host.
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Any attempt to access the AMU registers will result in an UNDEFINED
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exception being injected into the guest.
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