[PATCH v14 26/30] KVM: arm64: Add trace reset to the nVHE/pKVM hyp

Vincent Donnefort
2026-03-09T16:26:28Z

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@google.com>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 9c4fe3bfbfff..66abf77cf371 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 02d5271199d5..9b05f0c87586 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)
__tracing_update_clock(mult, shift, epoch_ns, epoch_cyc);
}

+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 2c8e6f49d7de..a6ca27b18e15 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)
--
2.53.0.473.g4a7958ca14-goog