linux-kernel - [PATCH v4 20/24] KVM: arm64: Add trace reset to the pKVM hyp

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Message-ID: <20250506164820.515876-21-vdonnefort@google.com>
Date: Tue,  6 May 2025 17:48:16 +0100
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, 
	kernel-team@...roid.com, linux-kernel@...r.kernel.org, 
	Vincent Donnefort <vdonnefort@...gle.com>
Subject: [PATCH v4 20/24] KVM: arm64: Add trace reset to the pKVM hyp

Let the hypervisor reset the trace buffer when triggered from the
tracefs file remotes/hypervisor/trace.

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 d122d79718a0..c40820a4b049 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -91,6 +91,7 @@ enum __kvm_host_smccc_func {
 	__KVM_HOST_SMCCC_FUNC___pkvm_load_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_unload_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_enable_tracing,
+	__KVM_HOST_SMCCC_FUNC___pkvm_reset_tracing,
 	__KVM_HOST_SMCCC_FUNC___pkvm_swap_reader_tracing,
 };
 
diff --git a/arch/arm64/kvm/hyp/include/nvhe/trace.h b/arch/arm64/kvm/hyp/include/nvhe/trace.h
index 4e11dcdf049b..0d2732f0d406 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -11,6 +11,7 @@ void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cy
 int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size);
 void __pkvm_unload_tracing(void);
 int __pkvm_enable_tracing(bool enable);
+int __pkvm_reset_tracing(unsigned int cpu);
 int __pkvm_swap_reader_tracing(unsigned int cpu);
 #else
 static inline void *tracing_reserve_entry(unsigned long length) { return NULL; }
@@ -21,6 +22,7 @@ void __pkvm_update_clock_tracing(u32 mult, u32 shift, u64 epoch_ns, u64 epoch_cy
 static inline int __pkvm_load_tracing(unsigned long desc_va, size_t desc_size) { return -ENODEV; }
 static inline void __pkvm_unload_tracing(void) { }
 static inline int __pkvm_enable_tracing(bool enable) { return -ENODEV; }
+static inline int __pkvm_reset_tracing(unsigned int cpu) { return -ENODEV; }
 static inline int __pkvm_swap_reader_tracing(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 c73229fb5e1b..65260bfd33ac 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -605,6 +605,13 @@ static void handle___pkvm_enable_tracing(struct kvm_cpu_context *host_ctxt)
 	cpu_reg(host_ctxt, 1) = __pkvm_enable_tracing(enable);
 }
 
+static void handle___pkvm_reset_tracing(struct kvm_cpu_context *host_ctxt)
+{
+	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
+
+	cpu_reg(host_ctxt, 1) = __pkvm_reset_tracing(cpu);
+}
+
 static void handle___pkvm_swap_reader_tracing(struct kvm_cpu_context *host_ctxt)
 {
 	DECLARE_REG(unsigned int, cpu, host_ctxt, 1);
@@ -655,6 +662,7 @@ static const hcall_t host_hcall[] = {
 	HANDLE_FUNC(__pkvm_load_tracing),
 	HANDLE_FUNC(__pkvm_unload_tracing),
 	HANDLE_FUNC(__pkvm_enable_tracing),
+	HANDLE_FUNC(__pkvm_reset_tracing),
 	HANDLE_FUNC(__pkvm_swap_reader_tracing),
 };
 
diff --git a/arch/arm64/kvm/hyp/nvhe/trace.c b/arch/arm64/kvm/hyp/nvhe/trace.c
index 32fd889315f0..b6d97237a7a0 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -230,6 +230,25 @@ int __pkvm_enable_tracing(bool enable)
 	return ret;
 }
 
+int __pkvm_reset_tracing(unsigned int cpu)
+{
+	int ret = 0;
+
+	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));
+	else
+		ret = -ENODEV;
+
+	hyp_spin_unlock(&trace_buffer.lock);
+
+	return ret;
+}
+
 int __pkvm_swap_reader_tracing(unsigned int cpu)
 {
 	int ret;
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 516d6c63c145..c7ad36212a7d 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -301,7 +301,7 @@ 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(__pkvm_reset_tracing, cpu);
 }
 
 static int hyp_trace_enable_event(unsigned short id, bool enable, void *priv)
-- 
2.49.0.967.g6a0df3ecc3-goog