[PATCH RFC v4 1/4] RISC-V: paravirt: Add pvqspinlock KVM backend

[GUO Ren (XuanTie)]

Add the KVM backend for the SBI PVLOCK (paravirt qspinlock kick_cpu)
extension. kvm_sbi_ext_pvlock_kick_cpu() kicks the target vCPU out of
the halted state via kvm_vcpu_kick(), and yields to it with
kvm_vcpu_yield_to() when the target is already runnable.

Reviewed-by: Leonardo Bras <leobras at redhat.com>
Signed-off-by: GUO Ren (XuanTie) <guoren at kernel.org>
---
 arch/riscv/include/asm/kvm_vcpu_sbi.h |  1 +
 arch/riscv/include/asm/sbi.h          |  5 ++++
 arch/riscv/include/uapi/asm/kvm.h     |  1 +
 arch/riscv/kvm/Makefile               |  1 +
 arch/riscv/kvm/vcpu_sbi.c             |  4 +++
 arch/riscv/kvm/vcpu_sbi_pvlock.c      | 54 +++++++++++++++++++++++++++++++++++
 6 files changed, 66 insertions(+)

diff --git a/arch/riscv/include/asm/kvm_vcpu_sbi.h b/arch/riscv/include/asm/kvm_vcpu_sbi.h
index f01a2860c751..cdc16e64ad19 100644
--- a/arch/riscv/include/asm/kvm_vcpu_sbi.h
+++ b/arch/riscv/include/asm/kvm_vcpu_sbi.h
@@ -114,6 +114,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_fwft;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_mpxy;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_experimental;
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_vendor;
+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pvlock;
 
 #ifdef CONFIG_RISCV_PMU_SBI
 extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pmu;
diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 5725e0ca4dda..724ab834ad85 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -38,6 +38,7 @@ enum sbi_ext_id {
 	SBI_EXT_FWFT = 0x46574654,
 	SBI_EXT_MPXY = 0x4D505859,
 	SBI_EXT_DBTR = 0x44425452,
+	SBI_EXT_PVLOCK = 0x50564C4B,
 
 	/* Experimentals extensions must lie within this range */
 	SBI_EXT_EXPERIMENTAL_START = 0x08000000,
@@ -534,6 +535,10 @@ union sbi_dbtr_shmem_entry {
 	struct sbi_dbtr_id_msg id;
 };
 
+enum sbi_ext_pvlock_fid {
+	SBI_EXT_PVLOCK_KICK_CPU = 0,
+};
+
 /* SBI spec version fields */
 #define SBI_SPEC_VERSION_DEFAULT	0x1
 #define SBI_SPEC_VERSION_MAJOR_SHIFT	24
diff --git a/arch/riscv/include/uapi/asm/kvm.h b/arch/riscv/include/uapi/asm/kvm.h
index 20d9959ca44f..110a0d62113f 100644
--- a/arch/riscv/include/uapi/asm/kvm.h
+++ b/arch/riscv/include/uapi/asm/kvm.h
@@ -228,6 +228,7 @@ 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_PVLOCK,
 	KVM_RISCV_SBI_EXT_MAX,
 };
 
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 296c2ba05089..404a4c5f8984 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -38,6 +38,7 @@ kvm-y += vcpu_sbi_sta.o
 kvm-y += vcpu_sbi_system.o
 kvm-$(CONFIG_RISCV_SBI_V01) += vcpu_sbi_v01.o
 kvm-y += vcpu_switch.o
+kvm-y += vcpu_sbi_pvlock.o
 kvm-y += vcpu_timer.o
 kvm-y += vcpu_vector.o
 kvm-y += vm.o
diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index 1c4f874368fb..07f72e619fd5 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -94,6 +94,10 @@ static const struct kvm_riscv_sbi_extension_entry sbi_ext[] = {
 		.ext_idx = KVM_RISCV_SBI_EXT_VENDOR,
 		.ext_ptr = &vcpu_sbi_ext_vendor,
 	},
+	{
+		.ext_idx = KVM_RISCV_SBI_EXT_PVLOCK,
+		.ext_ptr = &vcpu_sbi_ext_pvlock,
+	},
 };
 
 static const struct kvm_riscv_sbi_extension_entry *
diff --git a/arch/riscv/kvm/vcpu_sbi_pvlock.c b/arch/riscv/kvm/vcpu_sbi_pvlock.c
new file mode 100644
index 000000000000..728e59f3f18f
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_sbi_pvlock.c
@@ -0,0 +1,54 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (C) 2026 GUO Ren (XuanTie) <guoren at kernel.org>
+ */
+
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/kvm_host.h>
+#include <asm/sbi.h>
+#include <asm/kvm_vcpu_sbi.h>
+
+static int kvm_sbi_ext_pvlock_kick_cpu(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	struct kvm *kvm = vcpu->kvm;
+	struct kvm_vcpu *target;
+
+	target = kvm_get_vcpu_by_id(kvm, cp->a0);
+	if (!target)
+		return SBI_ERR_INVALID_PARAM;
+
+	kvm_vcpu_kick(target);
+
+	if (READ_ONCE(target->ready))
+		kvm_vcpu_yield_to(target);
+
+	return SBI_SUCCESS;
+}
+
+static int kvm_sbi_ext_pvlock_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
+				      struct kvm_vcpu_sbi_return *retdata)
+{
+	int ret = 0;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	unsigned long funcid = cp->a6;
+
+	switch (funcid) {
+	case SBI_EXT_PVLOCK_KICK_CPU:
+		ret = kvm_sbi_ext_pvlock_kick_cpu(vcpu);
+		break;
+	default:
+		ret = SBI_ERR_NOT_SUPPORTED;
+	}
+
+	retdata->err_val = ret;
+
+	return 0;
+}
+
+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_pvlock = {
+	.extid_start = SBI_EXT_PVLOCK,
+	.extid_end = SBI_EXT_PVLOCK,
+	.handler = kvm_sbi_ext_pvlock_handler,
+};

-- 
2.43.0