Messages in this thread | | | Date | Thu, 5 Oct 2023 19:05:01 +0100 | Subject | Re: [PATCH v2 5/6] arm64: KVM: Write TRFCR value on guest switch with nVHE | From | Suzuki K Poulose <> |
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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@arm.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
> + /* > + * 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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