When running with KVM protected mode, the hypervisor is able to generate
events into tracefs compatible ring-buffers. Create a trace remote so
the kernel can read those buffers.

This currently doesn't provide any event support which will come later.

Signed-off-by: Vincent Donnefort <redacted>

diff --git a/arch/arm64/kvm/Kconfig b/arch/arm64/kvm/Kconfig
index 580426cdbe77..64db254f0448 100644
--- a/arch/arm64/kvm/Kconfig
+++ b/arch/arm64/kvm/Kconfig

@@ -87,6 +87,7 @@ config PKVM_TRACING
 	bool
 	depends on KVM
 	depends on TRACING
+	select TRACE_REMOTE
 	select SIMPLE_RING_BUFFER
 	default y
 

diff --git a/arch/arm64/kvm/Makefile b/arch/arm64/kvm/Makefile
index 3ebc0570345c..2c184e3abd8e 100644
--- a/arch/arm64/kvm/Makefile
+++ b/arch/arm64/kvm/Makefile

@@ -30,6 +30,8 @@ kvm-$(CONFIG_HW_PERF_EVENTS)  += pmu-emul.o pmu.o
 kvm-$(CONFIG_ARM64_PTR_AUTH)  += pauth.o
 kvm-$(CONFIG_PTDUMP_STAGE2_DEBUGFS) += ptdump.o
 
+kvm-$(CONFIG_PKVM_TRACING) += hyp_trace.o
+
 always-y := hyp_constants.h hyp-constants.s
 
 define rule_gen_hyp_constants

diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c
index 870953b4a8a7..c485e54417e2 100644
--- a/arch/arm64/kvm/arm.c
+++ b/arch/arm64/kvm/arm.c

@@ -24,6 +24,7 @@
 
 #define CREATE_TRACE_POINTS
 #include "trace_arm.h"
+#include "hyp_trace.h"
 
 #include <linux/uaccess.h>
 #include <asm/ptrace.h>

@@ -2345,6 +2346,9 @@ static int __init init_subsystems(void)
 
 	kvm_register_perf_callbacks(NULL);
 
+	err = hyp_trace_init();
+	if (err)
+		kvm_err("Failed to initialize Hyp tracing\n");
 out:
 	if (err)
 		hyp_cpu_pm_exit();

diff --git a/arch/arm64/kvm/hyp_trace.c b/arch/arm64/kvm/hyp_trace.c
new file mode 100644
index 000000000000..98051c3fb0c2
--- /dev/null
+++ b/arch/arm64/kvm/hyp_trace.c

@@ -0,0 +1,210 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2025 Google LLC
+ * Author: Vincent Donnefort <vdonnefort@google.com>
+ */
+
+#include <linux/trace_remote.h>
+#include <linux/simple_ring_buffer.h>
+
+#include <asm/kvm_host.h>
+#include <asm/kvm_hyptrace.h>
+
+#include "hyp_trace.h"
+
+/* Access to this struct within the trace_remote_callbacks are protected by the trace_remote lock */
+static struct hyp_trace_buffer {
+	struct hyp_trace_desc	*desc;
+	size_t			desc_size;
+} trace_buffer;
+
+static int hyp_trace_buffer_alloc_bpages_backing(struct hyp_trace_buffer *trace_buffer, size_t size)
+{
+	int nr_bpages = (PAGE_ALIGN(size) / PAGE_SIZE) + 1;
+	size_t backing_size;
+	void *start;
+
+	backing_size = PAGE_ALIGN(sizeof(struct simple_buffer_page) * nr_bpages *
+				  num_possible_cpus());
+
+	start = alloc_pages_exact(backing_size, GFP_KERNEL_ACCOUNT);
+	if (!start)
+		return -ENOMEM;
+
+	trace_buffer->desc->bpages_backing_start = (unsigned long)start;
+	trace_buffer->desc->bpages_backing_size = backing_size;
+
+	return 0;
+}
+
+static void hyp_trace_buffer_free_bpages_backing(struct hyp_trace_buffer *trace_buffer)
+{
+	free_pages_exact((void *)trace_buffer->desc->bpages_backing_start,
+			 trace_buffer->desc->bpages_backing_size);
+}
+
+static int __load_page(unsigned long va)
+{
+	return kvm_call_hyp_nvhe(__pkvm_host_share_hyp, virt_to_pfn((void *)va), 1);
+}