Messages in this thread | ![/](/images/icornerl.gif) | | Date | Tue, 08 Aug 2023 12:04:19 +0100 | From | Marc Zyngier <> | Subject | Re: [RFC PATCH 2/3] arm64: KVM: Support exclude_guest for Coresight trace in nVHE |
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On Fri, 04 Aug 2023 11:13:12 +0100, James Clark <james.clark@arm.com> wrote: > > Currently trace will always be generated in nVHE as long as TRBE isn't > being used. To allow filtering out guest trace, re-apply the filter > rules before switching to the guest. > > The TRFCR restore function remains the same. > > Signed-off-by: James Clark <james.clark@arm.com> > --- > arch/arm64/kvm/debug.c | 7 ++++ > arch/arm64/kvm/hyp/nvhe/debug-sr.c | 56 +++++++++++++++++++++++++++--- > 2 files changed, 59 insertions(+), 4 deletions(-) > > diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c > index 8725291cb00a..ebb4db20a859 100644 > --- a/arch/arm64/kvm/debug.c > +++ b/arch/arm64/kvm/debug.c > @@ -335,10 +335,17 @@ void kvm_arch_vcpu_load_debug_state_flags(struct kvm_vcpu *vcpu) > 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_TRBE); > + /* > + * Save TRFCR on nVHE if FEAT_TRF exists. This will be done in cases > + * where DEBUG_STATE_SAVE_TRBE doesn't completely disable trace. > + */ > + 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) > { > vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_SPE); > vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRBE); > + vcpu_clear_flag(vcpu, DEBUG_STATE_SAVE_TRFCR); > } > diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > index 4558c02eb352..0e8c85b29b92 100644 > --- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c > +++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c > @@ -51,13 +51,17 @@ static void __debug_restore_spe(u64 pmscr_el1) > write_sysreg_s(pmscr_el1, SYS_PMSCR_EL1); > } > > -static void __debug_save_trace(u64 *trfcr_el1) > +/* > + * Save TRFCR and disable trace completely if TRBE is being used. Return true > + * if trace was disabled. > + */ > +static bool __debug_save_trace(u64 *trfcr_el1) > { > *trfcr_el1 = 0; > > /* Check if the TRBE is enabled */ > if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E)) > - return; > + return false;
While you're refactoring this code, please move the zeroing of *trfcr_el1 under the if statement.
> /* > * Prohibit trace generation while we are in guest. > * Since access to TRFCR_EL1 is trapped, the guest can't > @@ -68,6 +72,8 @@ static void __debug_save_trace(u64 *trfcr_el1) > isb(); > /* Drain the trace buffer to memory */ > tsb_csync(); > + > + return true; > } > > static void __debug_restore_trace(u64 trfcr_el1) > @@ -79,14 +85,55 @@ static void __debug_restore_trace(u64 trfcr_el1) > write_sysreg_s(trfcr_el1, SYS_TRFCR_EL1); > } > > +#if IS_ENABLED(CONFIG_PERF_EVENTS)
As previously stated, just always compile this. There shouldn't be anything here that's so large that it becomes a candidate for exclusion. Hell, even the whole of NV+pKVM are permanent features, even of most people won't use *any* of that.
> +static inline void __debug_save_trfcr(struct kvm_vcpu *vcpu) > +{ > + u64 trfcr; > + struct kvm_etm_event etm_event = vcpu->arch.host_debug_state.etm_event; > + > + /* No change if neither are excluded */ > + if (!etm_event.exclude_guest && !etm_event.exclude_host) { > + /* Zeroing prevents restoring a stale value */ > + vcpu->arch.host_debug_state.trfcr_el1 = 0;
I find this "zero means do nothing" part very odd. I can see it is already done, but I really dislike this sort of assumption to avoid writing to a register.
I'd really prefer we track another version of TRFCR_EL1, compare host and guest, and decide to avoid writing if they are equal. At least, it would be readable.
And in the end, expressing *everything* in terms of the register would really help, instead of the exclude_* stuff that has no place in the low-level arch code.
Thanks,
M.
-- Without deviation from the norm, progress is not possible.
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