The SBI headers define the Debug Triggers extension and its function IDs,
but KVM does not currently allow a VMM to expose DBTR to a guest.

Add DBTR to the KVM SBI extension list and forward its calls to userspace
through the existing KVM_EXIT_RISCV_SBI path. Keep the extension disabled
by default so that userspace must explicitly enable it through the SBI
extension ONE_REG interface before running the VCPU.

Signed-off-by: Xie Bo <xb@ultrarisc.com>
---
 arch/riscv/include/asm/kvm_vcpu_sbi.h | 1 +
 arch/riscv/include/uapi/asm/kvm.h     | 1 +
 arch/riscv/kvm/vcpu_sbi.c             | 4 ++++
 arch/riscv/kvm/vcpu_sbi_forward.c     | 7 +++++++
 4 files changed, 13 insertions(+)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index c1a7e3b40..53406b02f 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -104,6 +104,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_rfence;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_srst;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn;
+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbtr;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_susp;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_sta;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 504e73305..047d82f05 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -221,6 +221,7 @@ enum KVM_RISCV_SBI_EXT_ID {
 	KVM_RISCV_SBI_EXT_SUSP,
 	KVM_RISCV_SBI_EXT_FWFT,
 	KVM_RISCV_SBI_EXT_MPXY,
+	KVM_RISCV_SBI_EXT_DBTR,
 	KVM_RISCV_SBI_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index 46ab7b989..ed21239c5 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -70,6 +70,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
 		.ext_idx = KVM_RISCV_SBI_EXT_DBCN,
 		.ext_ptr = &vcpu_sbi_ext_dbcn,
 	},
+	{
+		.ext_idx = KVM_RISCV_SBI_EXT_DBTR,
+		.ext_ptr = &vcpu_sbi_ext_dbtr,
+	},
 	{
 		.ext_idx = KVM_RISCV_SBI_EXT_SUSP,
 		.ext_ptr = &vcpu_sbi_ext_susp,
diff --git a/arch/riscv/kvm/vcpu_sbi_forward.c b/arch/riscv/kvm/vcpu_sbi_forward.c
index 5a3c75eb2..8ac31b53f 100644
--- a/arch/riscv/kvm/vcpu_sbi_forward.c
+++ b/arch/riscv/kvm/vcpu_sbi_forward.c
@@ -26,6 +26,13 @@ const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbcn = {
 	.handler = kvm_riscv_vcpu_sbi_forward_handler,
 };
 
+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_dbtr = {
+	.extid_start = SBI_EXT_DBTR,
+	.extid_end = SBI_EXT_DBTR,
+	.default_disabled = true,
+	.handler = kvm_riscv_vcpu_sbi_forward_handler,
+};
+
 const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_mpxy = {
 	.extid_start = SBI_EXT_MPXY,
 	.extid_end = SBI_EXT_MPXY,

base-commit: b95f03f04d475aa6719d15a636ddf32222d55657
-- 
2.54.0