Messages in this thread | | | Date | Wed, 9 Aug 2023 15:20:58 +0100 | Subject | Re: [RFC PATCH 2/3] arm64: KVM: Support exclude_guest for Coresight trace in nVHE | From | James Clark <> |
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On 08/08/2023 12:04, Marc Zyngier wrote: > 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. >
Yep, I agree with all of the above, I can make these changes for the next version. I just want to clarify your point about disabling trace for protected guests when not in debug mode that I asked about in the review on patch 1.
> Thanks, > > M. >
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