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Message-ID: <Zz4c5LmQnK2SD5HO@linux.dev>
Date: Wed, 20 Nov 2024 17:31:16 +0000
From: Oliver Upton <oliver.upton@...ux.dev>
To: James Clark <james.clark@...aro.org>
Cc: suzuki.poulose@....com, coresight@...ts.linaro.org,
kvmarm@...ts.linux.dev, Marc Zyngier <maz@...nel.org>,
Joey Gouly <joey.gouly@....com>, Zenghui Yu <yuzenghui@...wei.com>,
Catalin Marinas <catalin.marinas@....com>,
Will Deacon <will@...nel.org>, Mike Leach <mike.leach@...aro.org>,
Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
Mark Rutland <mark.rutland@....com>,
Anshuman Khandual <anshuman.khandual@....com>,
"Rob Herring (Arm)" <robh@...nel.org>,
Shiqi Liu <shiqiliu@...t.edu.cn>, Fuad Tabba <tabba@...gle.com>,
James Morse <james.morse@....com>, Mark Brown <broonie@...nel.org>,
Raghavendra Rao Ananta <rananta@...gle.com>,
linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 11/12] KVM: arm64: Swap TRFCR on guest switch
On Tue, Nov 12, 2024 at 10:37:10AM +0000, James Clark wrote:
> +void kvm_set_trfcr(u64 host_trfcr, u64 guest_trfcr)
> +{
> + if (kvm_arm_skip_trace_state())
> + return;
> +
> + if (has_vhe())
> + write_sysreg_s(guest_trfcr, SYS_TRFCR_EL12);
> + else
> + if (host_trfcr != guest_trfcr) {
> + *host_data_ptr(host_debug_state.trfcr_el1) = guest_trfcr;
Huh? That's going into host_debug_state, which is the dumping grounds
for *host* context when entering a guest.
Not sure why we'd stick a *guest* value in there...
> + host_data_set_flag(HOST_STATE_SWAP_TRFCR);
> + } else
> + host_data_clear_flag(HOST_STATE_SWAP_TRFCR);
> +}
> +EXPORT_SYMBOL_GPL(kvm_set_trfcr);
I have a rather strong distaste for this interface, both with the
coresight driver and internally with the hypervisor. It'd be better if
the driver actually told KVM what the *intent* is rather than throwing a
pile of bits over the fence and forcing KVM to interpret what that
configuration means.
> +static void __debug_swap_trace(void)
> +{
> + u64 trfcr = read_sysreg_el1(SYS_TRFCR);
> +
> + write_sysreg_el1(*host_data_ptr(host_debug_state.trfcr_el1), SYS_TRFCR);
> + *host_data_ptr(host_debug_state.trfcr_el1) = trfcr;
> + host_data_set_flag(HOST_STATE_RESTORE_TRFCR);
> +}
> +
What if trace is disabled in the guest or in the host? Do we need to
synchronize when transitioning from an enabled -> disabled state like we
do today?
I took a stab at this, completely untested of course && punts on
protected mode. But this is _generally_ how I'd like to see everything
fit together.
diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
index 8bc0ec151684..b4714cece5f0 100644
--- a/arch/arm64/include/asm/kvm_host.h
+++ b/arch/arm64/include/asm/kvm_host.h
@@ -611,7 +611,7 @@ struct cpu_sve_state {
*/
struct kvm_host_data {
#define KVM_HOST_DATA_FLAG_HAS_SPE 0
-#define KVM_HOST_DATA_FLAG_HAS_TRBE 1
+#define KVM_HOST_DATA_FLAG_HOST_TRBE_ENABLED 1
#define KVM_HOST_DATA_FLAG_HOST_SVE_ENABLED 2
#define KVM_HOST_DATA_FLAG_HOST_SME_ENABLED 3
unsigned long flags;
@@ -659,6 +659,9 @@ struct kvm_host_data {
u64 mdcr_el2;
} host_debug_state;
+ /* Guest trace filter value */
+ u64 guest_trfcr_el1;
+
/* Number of programmable event counters (PMCR_EL0.N) for this CPU */
unsigned int nr_event_counters;
@@ -1381,6 +1384,8 @@ static inline bool kvm_pmu_counter_deferred(struct perf_event_attr *attr)
void kvm_set_pmu_events(u64 set, struct perf_event_attr *attr);
void kvm_clr_pmu_events(u64 clr);
bool kvm_set_pmuserenr(u64 val);
+void kvm_enable_trbe(u64 guest_trfcr);
+void kvm_disable_trbe(void);
#else
static inline void kvm_set_pmu_events(u64 set, struct perf_event_attr *attr) {}
static inline void kvm_clr_pmu_events(u64 clr) {}
@@ -1388,6 +1393,8 @@ static inline bool kvm_set_pmuserenr(u64 val)
{
return false;
}
+void kvm_enable_trbe(u64 guest_trfcr) {}
+void kvm_disable_trbe(void) {}
#endif
void kvm_vcpu_load_vhe(struct kvm_vcpu *vcpu);
diff --git a/arch/arm64/kvm/debug.c b/arch/arm64/kvm/debug.c
index 46dbeabd6833..6ef8d8f4b452 100644
--- a/arch/arm64/kvm/debug.c
+++ b/arch/arm64/kvm/debug.c
@@ -72,10 +72,6 @@ void kvm_init_host_debug_data(void)
if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_PMSVer_SHIFT) &&
!(read_sysreg_s(SYS_PMBIDR_EL1) & PMBIDR_EL1_P))
host_data_set_flag(HAS_SPE);
-
- if (cpuid_feature_extract_unsigned_field(dfr0, ID_AA64DFR0_EL1_TraceBuffer_SHIFT) &&
- !(read_sysreg_s(SYS_TRBIDR_EL1) & TRBIDR_EL1_P))
- host_data_set_flag(HAS_TRBE);
}
/*
@@ -215,3 +211,27 @@ void kvm_debug_handle_oslar(struct kvm_vcpu *vcpu, u64 val)
kvm_arch_vcpu_load(vcpu, smp_processor_id());
preempt_enable();
}
+
+void kvm_enable_trbe(u64 guest_trfcr)
+{
+ if (WARN_ON_ONCE(preemptible()))
+ return;
+
+ if (has_vhe()) {
+ write_sysreg_s(guest_trfcr, SYS_TRFCR_EL12);
+ return;
+ }
+
+ *host_data_ptr(guest_trfcr_el1) = guest_trfcr;
+ host_data_set_flag(HOST_TRBE_ENABLED);
+}
+EXPORT_SYMBOL_GPL(kvm_enable_trbe);
+
+void kvm_disable_trbe(void)
+{
+ if (has_vhe() || WARN_ON_ONCE(preemptible()))
+ return;
+
+ host_data_clear_flag(HOST_TRBE_ENABLED);
+}
+EXPORT_SYMBOL_GPL(kvm_disable_trbe);
diff --git a/arch/arm64/kvm/hyp/nvhe/debug-sr.c b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
index 858bb38e273f..d36cbce75bee 100644
--- a/arch/arm64/kvm/hyp/nvhe/debug-sr.c
+++ b/arch/arm64/kvm/hyp/nvhe/debug-sr.c
@@ -51,32 +51,33 @@ static void __debug_restore_spe(u64 pmscr_el1)
write_sysreg_el1(pmscr_el1, SYS_PMSCR);
}
-static void __debug_save_trace(u64 *trfcr_el1)
+static void __trace_do_switch(u64 *saved_trfcr, u64 new_trfcr)
{
- *trfcr_el1 = 0;
+ *saved_trfcr = read_sysreg_el1(SYS_TRFCR);
+ write_sysreg_el1(new_trfcr, SYS_TRFCR);
- /* Check if the TRBE is enabled */
- if (!(read_sysreg_s(SYS_TRBLIMITR_EL1) & TRBLIMITR_EL1_E))
+ /* Nothing left to do if going to an enabled state */
+ if (new_trfcr)
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.
+ * Switching to a context with trace generation disabled. Drain the
+ * trace buffer to memory.
*/
- *trfcr_el1 = read_sysreg_el1(SYS_TRFCR);
- write_sysreg_el1(0, SYS_TRFCR);
isb();
- /* Drain the trace buffer to memory */
tsb_csync();
}
-static void __debug_restore_trace(u64 trfcr_el1)
+static void __trace_switch_to_guest(void)
{
- if (!trfcr_el1)
- return;
+ __trace_do_switch(host_data_ptr(host_debug_state.trfcr_el1),
+ *host_data_ptr(guest_trfcr_el1));
+}
- /* Restore trace filter controls */
- write_sysreg_el1(trfcr_el1, SYS_TRFCR);
+static void __trace_switch_to_host(void)
+{
+ __trace_do_switch(host_data_ptr(guest_trfcr_el1),
+ *host_data_ptr(host_debug_state.trfcr_el1));
}
void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
@@ -84,9 +85,13 @@ void __debug_save_host_buffers_nvhe(struct kvm_vcpu *vcpu)
/* Disable and flush SPE data generation */
if (host_data_test_flag(HAS_SPE))
__debug_save_spe(host_data_ptr(host_debug_state.pmscr_el1));
- /* Disable and flush Self-Hosted Trace generation */
- if (host_data_test_flag(HAS_TRBE))
- __debug_save_trace(host_data_ptr(host_debug_state.trfcr_el1));
+
+ /*
+ * Switch the trace filter, potentially disabling and flushing trace
+ * data generation
+ */
+ if (host_data_test_flag(HOST_TRBE_ENABLED))
+ __trace_switch_to_guest();
}
void __debug_switch_to_guest(struct kvm_vcpu *vcpu)
@@ -98,8 +103,8 @@ void __debug_restore_host_buffers_nvhe(struct kvm_vcpu *vcpu)
{
if (host_data_test_flag(HAS_SPE))
__debug_restore_spe(*host_data_ptr(host_debug_state.pmscr_el1));
- if (host_data_test_flag(HAS_TRBE))
- __debug_restore_trace(*host_data_ptr(host_debug_state.trfcr_el1));
+ if (host_data_test_flag(HOST_TRBE_ENABLED))
+ __trace_switch_to_host();
}
void __debug_switch_to_host(struct kvm_vcpu *vcpu)
--
Thanks,
Oliver
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