linux-kernel - [PATCH v9 26/30] KVM: arm64: Add trace reset to the nVHE/pKVM hyp

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Message-ID: <20251202093623.2337860-27-vdonnefort@google.com>
Date: Tue,  2 Dec 2025 09:36:19 +0000
From: Vincent Donnefort <vdonnefort@...gle.com>
To: rostedt@...dmis.org, mhiramat@...nel.org, mathieu.desnoyers@...icios.com, 
	linux-trace-kernel@...r.kernel.org, maz@...nel.org, oliver.upton@...ux.dev, 
	joey.gouly@....com, suzuki.poulose@....com, yuzenghui@...wei.com
Cc: kvmarm@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	jstultz@...gle.com, qperret@...gle.com, will@...nel.org, 
	aneesh.kumar@...nel.org, kernel-team@...roid.com, 
	linux-kernel@...r.kernel.org, Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH v9 26/30] KVM: arm64: Add trace reset to the nVHE/pKVM hyp

Make the hypervisor reset either the whole tracing buffer or a specific
ring-buffer, on remotes/hypervisor/trace or per_cpu/<cpu>/trace write
access.

Signed-off-by: Vincent Donnefort <vdonnefort@...gle.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 375607c67285..a28b072125ec 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -94,6 +94,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___tracing_enable,
 	__KVM_HOST_SMCCC_FUNC___tracing_swap_reader,
 	__KVM_HOST_SMCCC_FUNC___tracing_update_clock,
+	__KVM_HOST_SMCCC_FUNC___tracing_reset,
 };
 
 #define DECLARE_KVM_VHE_SYM(sym)	extern char sym[]
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index fd641e1b1c23..44912869d184 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -12,6 +12,7 @@ void __tracing_unload(void);
 int __tracing_enable(bool enable);
 int __tracing_swap_reader(unsigned int cpu);
 void __tracing_update_clock(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc);
+int __tracing_reset(unsigned int cpu);
 #else
 static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
 static inline void tracing_commit_entry(void) { }
@@ -21,5 +22,6 @@ static inline void __tracing_unload(void) { }
 static inline int __tracing_enable(bool enable) { return -ENODEV; }
 static inline int __tracing_swap_reader(unsigned int cpu) { return -ENODEV; }
 static inline void __tracing_update_clock(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc) { }
+static inline int __tracing_reset(unsigned int cpu) { return -ENODEV; }
 #endif
 #endif
diff --git a/arch/arm64/kvm/hyp/nvhe/hyp-main.c b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
index 45b8f70828de..f92e82cbfcb4 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -625,6 +625,13 @@ static void handle___tracing_update_clock(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = 0;
 }
 
+static void handle___tracing_reset(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
+
+	cpu_reg(host_ctxt, 1) = __tracing_reset(cpu);
+}
+
 typedef void (*hcall_t)(struct kvm_cpu_context *);
 
 #define HANDLE_FUNC(x)	[__KVM_HOST_SMCCC_FUNC_##x] = (hcall_t)handle_##x
@@ -671,6 +678,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__tracing_enable),
 	HANDLE_FUNC(__tracing_swap_reader),
 	HANDLE_FUNC(__tracing_update_clock),
+	HANDLE_FUNC(__tracing_reset),
 };
 
 static void handle_host_hcall(struct kvm_cpu_context *host_ctxt)
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index 97e9f6c1a52c..93475cc36640 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -287,3 +287,20 @@ void __tracing_update_clock(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cyc)
 	/* ...we can now override the old one and swap. */
 	trace_clock_update(mult, shift, epoch_ns, epoch_cyc);
 }
+
+int __tracing_reset(unsigned int cpu)
+{
+	int ret = -ENODEV;
+
+	if (cpu >= hyp_nr_cpus)
+		return -EINVAL;
+
+	hyp_spin_lock(&trace_buffer.lock);
+
+	if (hyp_trace_buffer_loaded(&trace_buffer))
+		ret = simple_ring_buffer_reset(per_cpu_ptr(trace_buffer.simple_rbs, cpu));
+
+	hyp_spin_unlock(&trace_buffer.lock);
+
+	return ret;
+}
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 1e5fc27f0e9d..09bc192e3514 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -313,7 +313,7 @@ static int hyp_trace_swap_reader_page(unsigned int cpu, void *priv)
 
 static int hyp_trace_reset(unsigned int cpu, void *priv)
 {
-	return 0;
+	return kvm_call_hyp_nvhe(__tracing_reset, cpu);
 }
 
 static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
-- 
2.52.0.107.ga0afd4fd5b-goog