[PATCH 11/13] KVM: arm64: Add trace interface for hyp tracefs

[Vincent Donnefort]

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 <vdonnefort@xxxxxxxxxx>

diff --git a/arch/arm64/include/asm/kvm_asm.h b/arch/arm64/include/asm/kvm_asm.h
index 96490f8c3ff2..17896e6ceca7 100644
--- a/arch/arm64/include/asm/kvm_asm.h
+++ b/arch/arm64/include/asm/kvm_asm.h
@@ -83,6 +83,7 @@ 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 df17683a3b12..1004e1edf24f 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 7f5c3e888960..dc7a85922117 100644
--- a/arch/arm64/kvm/hyp/nvhe/hyp-main.c
+++ b/arch/arm64/kvm/hyp/nvhe/hyp-main.c
@@ -408,6 +408,13 @@ 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);
@@ -451,6 +458,7 @@ 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 022fe2e24f82..6ea0f1d475bb 100644
--- a/arch/arm64/kvm/hyp/nvhe/trace.c
+++ b/arch/arm64/kvm/hyp/nvhe/trace.c
@@ -284,12 +284,20 @@ static int rb_page_init(struct hyp_buffer_page *bpage, unsigned long hva)
 	return 0;
 }
 
+static void rb_page_reset(struct hyp_buffer_page *bpage)
+{
+	bpage->write = 0;
+	bpage->entries = 0;
+
+	local_set(&bpage->page->commit, 0);
+}
+
 static bool rb_cpu_loaded(struct hyp_rb_per_cpu *cpu_buffer)
 {
 	return !!cpu_buffer->bpages;
 }
 
-static void rb_cpu_disable_writing(struct hyp_rb_per_cpu *cpu_buffer)
+static int rb_cpu_disable_writing(struct hyp_rb_per_cpu *cpu_buffer)
 {
 	int prev_status;
 
@@ -299,6 +307,8 @@ static void rb_cpu_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 rb_cpu_enable_writing(struct hyp_rb_per_cpu *cpu_buffer)
@@ -311,6 +321,38 @@ static int rb_cpu_enable_writing(struct hyp_rb_per_cpu *cpu_buffer)
 	return 0;
 }
 
+static int rb_cpu_reset(struct hyp_rb_per_cpu *cpu_buffer)
+{
+	struct hyp_buffer_page *bpage;
+	int prev_status;
+
+	if (!rb_cpu_loaded(cpu_buffer))
+		return -ENODEV;
+
+	prev_status = rb_cpu_disable_writing(cpu_buffer);
+
+	bpage = cpu_buffer->head_page;
+	do {
+		rb_page_reset(bpage);
+		bpage = rb_next_page(bpage);
+	} while (bpage != cpu_buffer->head_page);
+
+	rb_page_reset(cpu_buffer->reader_page);
+
+	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)
+		rb_cpu_enable_writing(cpu_buffer);
+
+	return 0;
+}
+
 static void rb_cpu_teardown(struct hyp_rb_per_cpu *cpu_buffer)
 {
 	int i;
@@ -602,3 +644,17 @@ 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 = rb_cpu_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 0d0e5eada816..8ac8f9763cbd 100644
--- a/arch/arm64/kvm/hyp_trace.c
+++ b/arch/arm64/kvm/hyp_trace.c
@@ -196,6 +196,11 @@ 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;
@@ -354,6 +359,7 @@ static int hyp_trace_buffer_load(struct hyp_trace_buffer *hyp_buffer, size_t siz
 
 	hyp_buffer->writer.pdesc = &desc->page_desc;
 	hyp_buffer->writer.get_reader_page = __get_reader_page;
+	hyp_buffer->writer.reset = __reset;
 	hyp_buffer->trace_buffer = ring_buffer_reader(&hyp_buffer->writer);
 	if (!hyp_buffer->trace_buffer) {
 		ret = -ENOMEM;
@@ -820,6 +826,49 @@ static const struct file_operations hyp_trace_raw_fops = {
 	.llseek         = no_llseek,
 };
 
+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");
@@ -852,6 +901,9 @@ 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);
 
@@ -877,6 +929,9 @@ 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;
-- 
2.46.0.598.g6f2099f65c-goog