Re: [PATCH v2 4/6] arm64: KVM: Add interface to set guest value for TRFCR register

[James Clark]

On 05/10/2023 17:58, Suzuki K Poulose wrote:
> On 05/10/2023 13:57, James Clark wrote:
>> Add an interface for the Coresight driver to use to set the value of the
>> TRFCR register for the guest. This register controls the exclude
> 
> 
> 
>> settings for trace at different exception levels, and is used to
>> honor the exclude_host and exclude_guest parameters from the Perf
>> session. This will be used to later write TRFCR_EL1 on nVHE at guest
>> switch. For VHE, TRFCR_EL1 is written immediately. Because guest writes
> 
> minor nit: May be it would be clearer to say:
> 
> For VHE, the host trace is controlled by TRFCR_EL2 and thus we can
> write to the TRFCR_EL1 immediately. Because, ...
> 
>> to the register are trapped, the value will persist and can't be
>> modified.
>>
>> The settings must be copied to the vCPU before each run in the same
>> way that PMU events are because the per-cpu struct isn't accessible in
> 
> super minor nit:
> 
> way that PMU events are, because ...
> >> protected mode.
>>
>> Now that both guest and host values are saved, rename trfcr_el1 to
>> host_trfcr_el1 to make it clear that's the value that should be restored
> 
> This seems obsolete ? I couldn't find any reference to host_trfcr_el1
> anywhere ?
> 

Yep it was from an old version. I remove it and fixed all of the above too.

> Otherwise looks good to me.
> 
> Suzuki
> 


> 
>> on return to the host.
>>
>> Signed-off-by: James Clark <james.clark@xxxxxxx>
>> ---
>>   arch/arm64/include/asm/kvm_host.h |  3 +++
>>   arch/arm64/kvm/arm.c              |  1 +
>>   arch/arm64/kvm/debug.c            | 26 ++++++++++++++++++++++++++
>>   3 files changed, 30 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/kvm_host.h
>> b/arch/arm64/include/asm/kvm_host.h
>> index b5200f199692..8f2b4ec8ea61 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -1123,6 +1123,8 @@ void kvm_arch_vcpu_put_debug_state_flags(struct
>> kvm_vcpu *vcpu);
>>   void kvm_set_pmu_events(u32 set, struct perf_event_attr *attr);
>>   void kvm_clr_pmu_events(u32 clr);
>>   bool kvm_set_pmuserenr(u64 val);
>> +void kvm_etm_set_guest_trfcr(u64 trfcr_guest);
>> +void kvm_etm_update_vcpu_events(struct kvm_vcpu *vcpu);
>>   #else
>>   static inline void kvm_set_pmu_events(u32 set, struct
>> perf_event_attr *attr) {}
>>   static inline void kvm_clr_pmu_events(u32 clr) {}
>> @@ -1130,6 +1132,7 @@ static inline bool kvm_set_pmuserenr(u64 val)
>>   {
>>       return false;
>>   }
>> +static inline void kvm_etm_set_guest_trfcr(u64 trfcr_guest) {}
>>   #endif
>>     void kvm_vcpu_load_sysregs_vhe(struct kvm_vcpu *vcpu);
>> diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
>> index 78b0970eb8e6..22fab356b88f 100644
>> --- a/arch/arm64/kvm/arm.c
>> +++ b/arch/arm64/kvm/arm.c
>> @@ -1012,6 +1012,7 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu)
>>           kvm_vgic_flush_hwstate(vcpu);
>>             kvm_pmu_update_vcpu_events(vcpu);
>> +        kvm_etm_update_vcpu_events(vcpu);
>>             /*
>>            * Ensure we set mode to IN_GUEST_MODE after we disable
>> diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
>> index 6a1bad1a921b..19e722359154 100644
>> --- a/arch/arm64/kvm/debug.c
>> +++ b/arch/arm64/kvm/debug.c
>> @@ -23,6 +23,12 @@
>>     static DEFINE_PER_CPU(u64, mdcr_el2);
>>   +/*
>> + * Per CPU value for TRFCR that should be applied to any guest vcpu
>> that may
>> + * run on that core in the future.
>> + */
>> +static DEFINE_PER_CPU(u64, guest_trfcr);
>> +
>>   /**
>>    * save/restore_guest_debug_regs
>>    *
>> @@ -342,3 +348,23 @@ void kvm_arch_vcpu_put_debug_state_flags(struct
>> kvm_vcpu *vcpu)
>>       vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE);
>>       vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
>>   }
>> +
>> +void kvm_etm_set_guest_trfcr(u64 trfcr_guest)
>> +{
>> +    if (has_vhe())
>> +        write_sysreg_s(trfcr_guest, SYS_TRFCR_EL12);
>> +    else
>> +        *this_cpu_ptr(&guest_trfcr) = trfcr_guest;
>> +}
>> +EXPORT_SYMBOL_GPL(kvm_etm_set_guest_trfcr);
>> +
>> +/*
>> + * Updates the vcpu's view of the etm events for this cpu. Must be
>> + * called before every vcpu run after disabling interrupts, to ensure
>> + * that an interrupt cannot fire and update the structure.
>> + */
>> +void kvm_etm_update_vcpu_events(struct kvm_vcpu *vcpu)
>> +{
>> +    if (!has_vhe() && vcpu_get_flag(vcpu, DEBUG_STATE_SAVE_TRFCR))
>> +        ctxt_sys_reg(&vcpu->arch.ctxt, TRFCR_EL1) =
>> *this_cpu_ptr(&guest_trfcr);
>> +}
>