[09/11] KVM: arm64: Add trace interface for hyp tracefs

Commit Message

Vincent Donnefort Feb. 24, 2025, 12:13 p.m. UTC

The trace interface is solely here to reset tracing. Non-consuming read
is not yet supported due to the lack of support in the ring-buffer
meta page.

Signed-off-by: Vincent Donnefort <[e-mail]>

Patch

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 87d3e0e73b68..74f10847a55e 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_teardown_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 6f1cc571b47a..28bbb54b7a0b 100644
--- a/arch/arm64/kvm/hyp/include/nvhe/trace.h
+++ b/arch/arm64/kvm/hyp/include/nvhe/trace.h
@@ -20,6 +20,7 @@  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_teardown_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; }
@@ -30,6 +31,7 @@  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_teardown_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 a8b497b22407..e2419c97c57d 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_teardown_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 d79b6539377e..bf935645ed91 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -262,7 +262,7 @@  void tracing_commit_entry(void)
 	smp_store_release(&cpu_buffer->status, HYP_RB_READY);
 }
 
-static void hyp_rb_disable_writing(struct hyp_rb_per_cpu *cpu_buffer)
+static u32 hyp_rb_disable_writing(struct hyp_rb_per_cpu *cpu_buffer)
 {
 	u32 prev_status;
 
@@ -272,6 +272,8 @@  static void hyp_rb_disable_writing(struct hyp_rb_per_cpu *cpu_buffer)
 					      HYP_RB_READY,
 					      HYP_RB_UNAVAILABLE);
 	} while (prev_status == HYP_RB_WRITING);
+
+	return prev_status;
 }
 
 static int hyp_rb_enable_writing(struct hyp_rb_per_cpu *cpu_buffer)
@@ -284,6 +286,44 @@  static int hyp_rb_enable_writing(struct hyp_rb_per_cpu *cpu_buffer)
 	return 0;
 }
 
+static int hyp_rb_reset(struct hyp_rb_per_cpu *cpu_buffer)
+{
+	struct hyp_buffer_page *bpage;
+	u32 prev_status;
+
+	if (!hyp_rb_loaded(cpu_buffer))
+		return -ENODEV;
+
+	prev_status = hyp_rb_disable_writing(cpu_buffer);
+
+	while (!hyp_bpage_is_head(cpu_buffer->head_page))
+		cpu_buffer->head_page = hyp_bpage_next_page(cpu_buffer->head_page);
+
+	bpage = cpu_buffer->tail_page = cpu_buffer->head_page;
+	do {
+		hyp_bpage_reset(bpage);
+		bpage = hyp_bpage_next_page(bpage);
+	} while (bpage != cpu_buffer->head_page);
+
+	hyp_bpage_reset(cpu_buffer->reader_page);
+
+	cpu_buffer->last_overrun = 0;
+	cpu_buffer->write_stamp = 0;
+
+	cpu_buffer->meta->reader.read = 0;
+	cpu_buffer->meta->reader.lost_events = 0;
+	cpu_buffer->meta->entries = 0;
+	cpu_buffer->meta->overrun = 0;
+	cpu_buffer->meta->read = 0;
+	meta_pages_lost(cpu_buffer->meta) = 0;
+	meta_pages_touched(cpu_buffer->meta) = 0;
+
+	if (prev_status == HYP_RB_READY)
+		hyp_rb_enable_writing(cpu_buffer);
+
+	return 0;
+}
+
 static void hyp_rb_teardown(struct hyp_rb_per_cpu *cpu_buffer)
 {
 	int i;
@@ -572,3 +612,17 @@  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_rb_lock);
+	ret = hyp_rb_reset(per_cpu_ptr(&trace_rb, cpu));
+	hyp_spin_unlock(&trace_rb_lock);
+
+	return ret;
+}
diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
index 38d97e34eada..03a6813cbe66 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -200,6 +200,11 @@  static int __get_reader_page(int cpu)
 	return kvm_call_hyp_nvhe(__pkvm_swap_reader_tracing, cpu);
 }
 
+static int __reset(int cpu)
+{
+	return kvm_call_hyp_nvhe(__pkvm_reset_tracing, cpu);
+}
+
 static void hyp_trace_free_pages(struct hyp_trace_desc *desc)
 {
 	struct rb_page_desc *rb_desc;
@@ -361,6 +366,7 @@  static int hyp_trace_buffer_load(struct hyp_trace_buffer *hyp_buffer, size_t siz
 
 	hyp_buffer->remote.pdesc = &desc->page_desc;
 	hyp_buffer->remote.get_reader_page = __get_reader_page;
+	hyp_buffer->remote.reset = __reset;
 	hyp_buffer->trace_buffer = ring_buffer_remote(&hyp_buffer->remote);
 	if (!hyp_buffer->trace_buffer) {
 		ret = -ENOMEM;
@@ -825,6 +831,49 @@  static const struct file_operations hyp_trace_raw_fops = {
 	.release        = hyp_trace_raw_release,
 };
 
+static void hyp_trace_reset(int cpu)
+{
+	struct hyp_trace_buffer *hyp_buffer = &hyp_trace_buffer;
+
+	mutex_lock(&hyp_buffer->lock);
+
+	if (!hyp_trace_buffer_loaded(hyp_buffer))
+		goto out;
+
+	if (cpu == RING_BUFFER_ALL_CPUS)
+		ring_buffer_reset(hyp_buffer->trace_buffer);
+	else
+		ring_buffer_reset_cpu(hyp_buffer->trace_buffer, cpu);
+
+out:
+	mutex_unlock(&hyp_buffer->lock);
+}
+
+static int hyp_trace_open(struct inode *inode, struct file *file)
+{
+	int cpu = (s64)inode->i_private;
+
+	if (file->f_mode & FMODE_WRITE) {
+		hyp_trace_reset(cpu);
+
+		return 0;
+	}
+
+	return -EPERM;
+}
+
+static ssize_t hyp_trace_write(struct file *filp, const char __user *ubuf,
+			       size_t count, loff_t *ppos)
+{
+	return count;
+}
+
+static const struct file_operations hyp_trace_fops = {
+	.open           = hyp_trace_open,
+	.write          = hyp_trace_write,
+	.release        = NULL,
+};
+
 static int hyp_trace_clock_show(struct seq_file *m, void *v)
 {
 	seq_puts(m, "[boot]\n");
@@ -857,6 +906,9 @@  int hyp_trace_init_tracefs(void)
 	tracefs_create_file("trace_pipe", TRACEFS_MODE_WRITE, root,
 			    (void *)RING_BUFFER_ALL_CPUS, &hyp_trace_pipe_fops);
 
+	tracefs_create_file("trace", TRACEFS_MODE_WRITE, root,
+			    (void *)RING_BUFFER_ALL_CPUS, &hyp_trace_fops);
+
 	tracefs_create_file("trace_clock", TRACEFS_MODE_READ, root, NULL,
 			    &hyp_trace_clock_fops);
 
@@ -882,6 +934,9 @@  int hyp_trace_init_tracefs(void)
 
 		tracefs_create_file("trace_pipe_raw", TRACEFS_MODE_READ, per_cpu_dir,
 				    (void *)cpu, &hyp_trace_pipe_fops);
+
+		tracefs_create_file("trace", TRACEFS_MODE_READ, per_cpu_dir,
+				    (void *)cpu, &hyp_trace_fops);
 	}
 
 	return 0;