Hi Ionela, On 26/02/2020 13:29, 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. > diff --git a/arch/arm64/mm/proc.S b/arch/arm64/mm/proc.S > index aafed6902411..7103027b4e64 100644 > --- a/arch/arm64/mm/proc.S > +++ b/arch/arm64/mm/proc.S > @@ -131,6 +131,7 @@ alternative_endif > ubfx x11, x11, #1, #1 > msr oslar_el1, x11 > reset_pmuserenr_el0 x0 // Disable PMU access from EL0 > + reset_amuserenr_el0 x0 // Disable AMU access from EL0 > > alternative_if ARM64_HAS_RAS_EXTN > msr_s SYS_DISR_EL1, xzr (This above hunk is in: cpu_do_resume, and this next one is __cpu_setup,) > @@ -423,6 +424,8 @@ SYM_FUNC_START(__cpu_setup) > isb // Unmask debug exceptions now, > enable_dbg // since this is per-cpu > reset_pmuserenr_el0 x0 // Disable PMU access from EL0 > + reset_amuserenr_el0 x0 // Disable AMU access from EL0 I think you only need this in __cpu_setup. The entry-point from cpu-idle calls: | cpu_resume | ->__cpu_setup | -->reset_amuserenr_el0 | ->_cpu_resume | -->cpu_do_resume | --->reset_amuserenr_el0 (Which means the PMU reset call is redundant too). Its harmless, and needs cleaning up already, so regardless: Reviewed-by: James Morse <james.morse@xxxxxxx> Thanks, James
