Messages in this thread | | | Subject | Re: [PATCH v3 2/7] arm64: trap to EL1 accesses to AMU counters from EL0 | From | Suzuki Kuruppassery Poulose <> | Date | Wed, 12 Feb 2020 11:44:59 +0000 |
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On 11/02/2020 18:45, Ionela Voinescu wrote: > The activity monitors extension is an optional extension introduced > by the ARMv8.4 CPU architecture. In order to access the activity > monitors counters safely, if desired, the kernel should detect the > presence of the extension through the feature register, and mediate > the access. > > Therefore, disable direct accesses to activity monitors counters > from EL0 (userspace) and trap them to EL1 (kernel). > > To be noted that the ARM64_AMU_EXTN kernel config and the disable_amu > kernel parameter do not have an effect on this code. Given that the > amuserenr_el0 resets to an UNKNOWN value, setting the trap of EL0 > accesses to EL1 is always attempted for safety and security > considerations. Therefore firmware should still ensure accesses to > AMU registers are not trapped in EL2/EL3 as this code cannot be > bypassed if the CPU implements the Activity Monitors Unit. > > Signed-off-by: Ionela Voinescu <ionela.voinescu@arm.com> > Cc: Catalin Marinas <catalin.marinas@arm.com> > Cc: Will Deacon <will@kernel.org> > Cc: Mark Rutland <mark.rutland@arm.com> > Cc: Steve Capper <steve.capper@arm.com> > ---
Reviewed-by: Suzuki K Poulose <suzuki.poulose@arm.com>
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