HACK: Install a trampoline instruction into pvmfw memory

In order to aid testing on systems that provide an empty pvmfw carveout,
install a single trampoline instruction from the host prior to
deprivilege which simply branches to the address in X4.

Signed-off-by: Will Deacon <will@kernel.org>

arch/arm64/kvm/pkvm.c

diff --git a/arch/arm64/kvm/pkvm.c b/arch/arm64/kvm/pkvm.c
index b769a88..a795efab1 100644
--- a/arch/arm64/kvm/pkvm.c
+++ b/arch/arm64/kvm/pkvm.c
@@ -314,3 +314,21 @@ int kvm_init_pvm(struct kvm *kvm, unsigned long type)
 	kvm->arch.pkvm.enabled = true;
 	return 0;
 }
+
+static int BODGE_install_loader(void)
+{
+	void *addr;
+
+	if (!pkvm_firmware_mem)
+		return -ENOMEM;
+
+	addr = memremap(pkvm_firmware_mem->base, PAGE_SIZE, MEMREMAP_WB);
+	if (!addr)
+		return -EFAULT;
+
+	pr_info("!! Installing dummy pvmfw into reserved memory region...\n");
+	((u32 *)addr)[0] = 0xd61f0080; // BR	X4
+	memunmap(addr);
+	return 0;
+}
+arch_initcall(BODGE_install_loader);