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Message-ID: <ec50ef51-e0f7-90f5-2c4a-01754e3b70ad@arm.com>
Date: Thu, 19 Oct 2023 17:59:01 +0100
From: James Clark <james.clark@....com>
To: Suzuki K Poulose <suzuki.poulose@....com>
Cc: Oliver Upton <oliver.upton@...ux.dev>,
James Morse <james.morse@....com>,
Zenghui Yu <yuzenghui@...wei.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>,
Mike Leach <mike.leach@...aro.org>,
Leo Yan <leo.yan@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Rob Herring <robh@...nel.org>,
Jintack Lim <jintack.lim@...aro.org>,
Akihiko Odaki <akihiko.odaki@...nix.com>,
Fuad Tabba <tabba@...gle.com>, Joey Gouly <joey.gouly@....com>,
linux-kernel@...r.kernel.org, coresight@...ts.linaro.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
broonie@...nel.org, maz@...nel.org
Subject: Re: [PATCH v2 5/6] arm64: KVM: Write TRFCR value on guest switch with
nVHE
On 05/10/2023 19:05, Suzuki K Poulose wrote:
> On 05/10/2023 13:57, 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@....com>
>> ---
>> arch/arm64/include/asm/kvm_hyp.h | 6 ++-
>> arch/arm64/kvm/debug.c | 13 +++++-
>> arch/arm64/kvm/hyp/nvhe/debug-sr.c | 63 ++++++++++++++++++------------
>> arch/arm64/kvm/hyp/nvhe/switch.c | 4 +-
>> 4 files changed, 57 insertions(+), 29 deletions(-)
>>
>> diff --git a/arch/arm64/include/asm/kvm_hyp.h
>> b/arch/arm64/include/asm/kvm_hyp.h
>> index 37e238f526d7..0383fd3d60b5 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/debug.c b/arch/arm64/kvm/debug.c
>> index 19e722359154..d949dd354464 100644
>> --- a/arch/arm64/kvm/debug.c
>> +++ b/arch/arm64/kvm/debug.c
>> @@ -337,10 +337,21 @@ void kvm_arch_vcpu_load_debug_state_flags(struct
>> kvm_vcpu *vcpu)
>> !(read_sysreg_s(SYS_PMBIDR_EL1) & BIT(PMBIDR_EL1_P_SHIFT)))
>> vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_SPE);
>> - /* Check if we have TRBE implemented and available at the host */
>> + /*
>> + * Check if we have TRBE implemented and available at the host.
>> If it's
>> + * in use at the time of guest switch it will need to be disabled
>> and
>> + * then restored.
>> + */
>> if (cpuid_feature_extract_unsigned_field(dfr0,
>> ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
>> !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
>> vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
>
> As per A3.1 Armv9-A architecture extensions (DDI 0487J.a), FEAT_TRBE
> mandates FEAT_TRF. So, we could check FEAT_TRF and if we have a hit,
> skip the TRBE checks. But, having read the code below, it looks like
> we need separate flags for TRFCR and TRBE.
>
>> + /*
>> + * Also save TRFCR on nVHE if FEAT_TRF (TraceFilt) exists. This
>> will be
>> + * done in cases where use of TRBE doesn't completely disable
>> trace and
>> + * handles the exclude_host/exclude_guest rules of the trace
>> session.
>> + */
>> + if (cpuid_feature_extract_unsigned_field(dfr0,
>> ID_AA64DFR0_EL1_TraceFilt_SHIFT))
>> + vcpu_set_flag(vcpu, DEBUG_STATE_SAVE_TRFCR);
>
>> }
>> void kvm_arch_vcpu_put_debug_state_flags(struct kvm_vcpu *vcpu)
>> diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
>> b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
>> index 128a57dddabf..c6252029c277 100644
>> --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
>> +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
>> @@ -51,42 +51,56 @@ 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 (read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E) {
>
> This is problematic. At this point, we are not sure if TRBE is available
> or not (e.g. we could be on a v8.4 CPU or a v9.0 with TRBE disabled by
> higher EL). May be we need to add a separate flag to indicate the
> presence of TRBE.
>
> Suzuki
>
Fixed in V3
>> + /*
>> + * 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_TRFCR))
>> - __debug_save_trace(host_ctxt);
>> + __debug_save_trace(host_ctxt, guest_ctxt);
>> }
>> void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
>> @@ -94,12 +108,13 @@ 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_TRFCR))
>> - __debug_restore_trace(host_ctxt);
>> + __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 c8f15e4dab19..55207ec31bd3 100644
>> --- a/arch/arm64/kvm/hyp/nvhe/switch.c
>> +++ b/arch/arm64/kvm/hyp/nvhe/switch.c
>> @@ -276,7 +276,7 @@ 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
>> @@ -343,7 +343,7 @@ 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);
>
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