KVM: arm64: Fix nVHE/pKVM hyp tracing error on invalid desc

pKVM must validate the host-provided tracing buffer descriptor.
However, if an error is found, the hypervisor would just return 0 to the
host. Fix the return value on validation failure.

While at it, rename the function to hyp_trace_desc_is_valid() and skip
validation for the nVHE mode as we trust host-provided data in that
case.

Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Fixes: 680a04c ("KVM: arm64: Add tracing capability for the nVHE/pKVM hyp")
Link: https://lore.kernel.org/r/20260514162624.3477857-1-vdonnefort@google.com
Signed-off-by: Marc Zyngier <maz@kernel.org>

Author: vdonnefort

arch/arm64/kvm/hyp/nvhe/trace.c

@@ -164,13 +164,16 @@ static int hyp_trace_buffer_load(struct hyp_trace_buffer *trace_buffer,
 	return ret;
 }
 
-static bool hyp_trace_desc_validate(struct hyp_trace_desc *desc, size_t desc_size)
+static bool hyp_trace_desc_is_valid(struct hyp_trace_desc *desc, size_t desc_size)
 {
 	struct ring_buffer_desc *rb_desc;
 	unsigned int cpu;
 	size_t nr_bpages;
 	void *desc_end;
 
+	if (!is_protected_kvm_enabled())
+		return true;
+
 	/*
 	 * Both desc_size and bpages_backing_size are untrusted host-provided
 	 * values. We rely on __pkvm_host_donate_hyp() to enforce their validity.
@@ -212,8 +215,10 @@ int __tracing_load(unsigned long desc_hva, size_t desc_size)
 	if (ret)
 		return ret;
 
-	if (!hyp_trace_desc_validate(desc, desc_size))
+	if (!hyp_trace_desc_is_valid(desc, desc_size)) {
+		ret = -EINVAL;
 		goto err_release_desc;
+	}
 
 	hyp_spin_lock(&trace_buffer.lock);