Re: [PATCH v3 5/6] arm64: KVM: Write TRFCR value on guest switch with nVHE

[Suzuki K Poulose]

On 19/10/2023 17:55, James Clark wrote:
> The guest value for TRFCR requested by the Coresight driver is saved
> in sysregs[TRFCR_EL1]. On guest switch this value needs to be written to
> the register. Currently TRFCR is only modified when we want to disable
> trace completely in guests due to an issue with TRBE. Expand the
> __debug_save_trace() function to always write to the register if a
> different value for guests is required, but also keep the existing TRBE
> disable behavior if that's required.
>
> The TRFCR restore function remains functionally the same, except a value
> of 0 doesn't mean "don't restore" anymore. Now that we save both guest
> and host values the register is restored any time the guest and host
> values differ.
>
> Signed-off-by: James Clark <james.clark@xxxxxxx>

Looks good to me.

Reviewed-by: Suzuki K Poulose <suzuki.poulose@xxxxxxx>


> ---
>   arch/arm64/include/asm/kvm_hyp.h   |  6 ++-
>   arch/arm64/kvm/hyp/nvhe/debug-sr.c | 68 ++++++++++++++++++------------
>   arch/arm64/kvm/hyp/nvhe/switch.c   |  4 +-
>   3 files changed, 48 insertions(+), 30 deletions(-)
>
> diff --git a/arch/arm64/include/asm/kvm_hyp.h b/arch/arm64/include/asm/kvm_hyp.h
> index 52ac90d419e7..6286e580696e 100644
> --- a/arch/arm64/include/asm/kvm_hyp.h
> +++ b/arch/arm64/include/asm/kvm_hyp.h
> @@ -103,8 +103,10 @@ void __debug_switch_to_guest(struct kvm_vcpu *vcpu);
>   void __debug_switch_to_host(struct kvm_vcpu *vcpu);
>   
>   #ifdef __KVM_NVHE_HYPERVISOR__
> -void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt);
> -void __debug_restore_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt);
> +void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt,
> +				    struct kvm_cpu_context *guest_ctxt);
> +void __debug_restore_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt,
> +				       struct kvm_cpu_context *guest_ctxt);
>   #endif
>   
>   void __fpsimd_save_state(struct user_fpsimd_state *fp_regs);
> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> index f389ee59788c..6174f710948e 100644
> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
> @@ -51,42 +51,57 @@ static void __debug_restore_spe(struct kvm_cpu_context *host_ctxt)
>   	write_sysreg_s(ctxt_sys_reg(host_ctxt, PMSCR_EL1), SYS_PMSCR_EL1);
>   }
>   
> -static void __debug_save_trace(struct kvm_cpu_context *host_ctxt)
> +/*
> + * Save TRFCR and disable trace completely if TRBE is being used, otherwise
> + * apply required guest TRFCR value.
> + */
> +static void __debug_save_trace(struct kvm_cpu_context *host_ctxt,
> +			       struct kvm_cpu_context *guest_ctxt)
>   {
> -	ctxt_sys_reg(host_ctxt, TRFCR_EL1) = 0;
> +	ctxt_sys_reg(host_ctxt, TRFCR_EL1) = read_sysreg_s(SYS_TRFCR_EL1);
>   
>   	/* Check if the TRBE is enabled */
> -	if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E))
> -		return;
> -	/*
> -	 * Prohibit trace generation while we are in guest.
> -	 * Since access to TRFCR_EL1 is trapped, the guest can't
> -	 * modify the filtering set by the host.
> -	 */
> -	ctxt_sys_reg(host_ctxt, TRFCR_EL1) = read_sysreg_s(SYS_TRFCR_EL1);
> -	write_sysreg_s(0, SYS_TRFCR_EL1);
> -	isb();
> -	/* Drain the trace buffer to memory */
> -	tsb_csync();
> +	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRBE) &&
> +	    (read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E)) {
> +		/*
> +		 * Prohibit trace generation while we are in guest. Since access
> +		 * to TRFCR_EL1 is trapped, the guest can't modify the filtering
> +		 * set by the host.
> +		 */
> +		ctxt_sys_reg(guest_ctxt, TRFCR_EL1) = 0;
> +		write_sysreg_s(0, SYS_TRFCR_EL1);
> +		isb();
> +		/* Drain the trace buffer to memory */
> +		tsb_csync();
> +	} else {
> +		/*
> +		 * Not using TRBE, so guest trace works. Apply the guest filters
> +		 * provided by the Coresight driver, if different.
> +		 */
> +		if (ctxt_sys_reg(host_ctxt, TRFCR_EL1) !=
> +		    ctxt_sys_reg(guest_ctxt, TRFCR_EL1))
> +			write_sysreg_s(ctxt_sys_reg(guest_ctxt, TRFCR_EL1),
> +				       SYS_TRFCR_EL1);
> +	}
>   }
>   
> -static void __debug_restore_trace(struct kvm_cpu_context *host_ctxt)
> +static void __debug_restore_trace(struct kvm_cpu_context *host_ctxt,
> +				  struct kvm_cpu_context *guest_ctxt)
>   {
> -	if (!ctxt_sys_reg(host_ctxt, TRFCR_EL1))
> -		return;
> -
>   	/* Restore trace filter controls */
> -	write_sysreg_s(ctxt_sys_reg(host_ctxt, TRFCR_EL1), SYS_TRFCR_EL1);
> +	if (ctxt_sys_reg(host_ctxt, TRFCR_EL1) != ctxt_sys_reg(guest_ctxt, TRFCR_EL1))
> +		write_sysreg_s(ctxt_sys_reg(host_ctxt, TRFCR_EL1), SYS_TRFCR_EL1);
>   }
>   
> -void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt)
> +void __debug_save_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt,
> +				    struct kvm_cpu_context *guest_ctxt)
>   {
>   	/* Disable and flush SPE data generation */
>   	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_SPE))
>   		__debug_save_spe(host_ctxt);
> -	/* Disable and flush Self-Hosted Trace generation */
> -	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRBE))
> -		__debug_save_trace(host_ctxt);
> +
> +	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRFCR))
> +		__debug_save_trace(host_ctxt, guest_ctxt);
>   }
>   
>   void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
> @@ -94,12 +109,13 @@ void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
>   	__debug_switch_to_guest_common(vcpu);
>   }
>   
> -void __debug_restore_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt)
> +void __debug_restore_host_buffers_nvhe(struct kvm_cpu_context *host_ctxt,
> +				       struct kvm_cpu_context *guest_ctxt)
>   {
>   	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_SPE))
>   		__debug_restore_spe(host_ctxt);
> -	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRBE))
> -		__debug_restore_trace(host_ctxt);
> +	if (vcpu_get_flag(host_ctxt->__hyp_running_vcpu, DEBUG_STATE_SAVE_TRFCR))
> +		__debug_restore_trace(host_ctxt, guest_ctxt);
>   }
>   
>   void __debug_switch_to_host(struct kvm_vcpu *vcpu)
> diff --git a/arch/arm64/kvm/hyp/nvhe/switch.c b/arch/arm64/kvm/hyp/nvhe/switch.c
> index 6b4b24ae077f..c7bea5cf672d 100644
> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
> @@ -278,7 +278,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>   	 * translation regime to EL2 (via MDCR_EL2_E2PB == 0) and
>   	 * before we load guest Stage1.
>   	 */
> -	__debug_save_host_buffers_nvhe(host_ctxt);
> +	__debug_save_host_buffers_nvhe(host_ctxt, guest_ctxt);
>   
>   	/*
>   	 * We're about to restore some new MMU state. Make sure
> @@ -345,7 +345,7 @@ int __kvm_vcpu_run(struct kvm_vcpu *vcpu)
>   	 * This must come after restoring the host sysregs, since a non-VHE
>   	 * system may enable SPE here and make use of the TTBRs.
>   	 */
> -	__debug_restore_host_buffers_nvhe(host_ctxt);
> +	__debug_restore_host_buffers_nvhe(host_ctxt, guest_ctxt);
>   
>   	if (pmu_switch_needed)
>   		__pmu_switch_to_host(vcpu);