RISC-V: KVM: Add SBI HSM extension in KVM

SBI HSM extension allows OS to start/stop harts any time. It also allows
ordered booting of harts instead of random booting.

Implement SBI HSM exntesion and designate the vcpu 0 as the boot vcpu id.
All other non-zero non-booting vcpus should be brought up by the OS
implementing HSM extension. If the guest OS doesn't implement HSM
extension, only single vcpu will be available to OS.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>

1 files changed, 105 insertions, 0 deletions

diff --git a/arch/riscv/kvm/vcpu_sbi_hsm.c b/arch/riscv/kvm/vcpu_sbi_hsm.c
new file mode 100644
index 000000000000..2e383687fa48
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_sbi_hsm.c
@@ -0,0 +1,105 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2021 Western Digital Corporation or its affiliates.
+ *
+ * Authors:
+ *     Atish Patra <atish.patra@wdc.com>
+ */
+
+#include <linux/errno.h>
+#include <linux/err.h>
+#include <linux/kvm_host.h>
+#include <asm/csr.h>
+#include <asm/sbi.h>
+#include <asm/kvm_vcpu_sbi.h>
+
+static int kvm_sbi_hsm_vcpu_start(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpu_context *reset_cntx;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	struct kvm_vcpu *target_vcpu;
+	unsigned long target_vcpuid = cp->a0;
+
+	target_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, target_vcpuid);
+	if (!target_vcpu)
+		return -EINVAL;
+	if (!target_vcpu->arch.power_off)
+		return -EALREADY;
+
+	reset_cntx = &target_vcpu->arch.guest_reset_context;
+	/* start address */
+	reset_cntx->sepc = cp->a1;
+	/* target vcpu id to start */
+	reset_cntx->a0 = target_vcpuid;
+	/* private data passed from kernel */
+	reset_cntx->a1 = cp->a2;
+	kvm_make_request(KVM_REQ_VCPU_RESET, target_vcpu);
+
+	kvm_riscv_vcpu_power_on(target_vcpu);
+
+	return 0;
+}
+
+static int kvm_sbi_hsm_vcpu_stop(struct kvm_vcpu *vcpu)
+{
+	if (vcpu->arch.power_off)
+		return -EINVAL;
+
+	kvm_riscv_vcpu_power_off(vcpu);
+
+	return 0;
+}
+
+static int kvm_sbi_hsm_vcpu_get_status(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	unsigned long target_vcpuid = cp->a0;
+	struct kvm_vcpu *target_vcpu;
+
+	target_vcpu = kvm_get_vcpu_by_id(vcpu->kvm, target_vcpuid);
+	if (!target_vcpu)
+		return -EINVAL;
+	if (!target_vcpu->arch.power_off)
+		return SBI_HSM_HART_STATUS_STARTED;
+	else
+		return SBI_HSM_HART_STATUS_STOPPED;
+}
+
+static int kvm_sbi_ext_hsm_handler(struct kvm_vcpu *vcpu, struct kvm_run *run,
+				   unsigned long *out_val,
+				   struct kvm_cpu_trap *utrap,
+				   bool *exit)
+{
+	int ret = 0;
+	struct kvm_cpu_context *cp = &vcpu->arch.guest_context;
+	struct kvm *kvm = vcpu->kvm;
+	unsigned long funcid = cp->a6;
+
+	switch (funcid) {
+	case SBI_EXT_HSM_HART_START:
+		mutex_lock(&kvm->lock);
+		ret = kvm_sbi_hsm_vcpu_start(vcpu);
+		mutex_unlock(&kvm->lock);
+		break;
+	case SBI_EXT_HSM_HART_STOP:
+		ret = kvm_sbi_hsm_vcpu_stop(vcpu);
+		break;
+	case SBI_EXT_HSM_HART_STATUS:
+		ret = kvm_sbi_hsm_vcpu_get_status(vcpu);
+		if (ret >= 0) {
+			*out_val = ret;
+			ret = 0;
+		}
+		break;
+	default:
+		ret = -EOPNOTSUPP;
+	}
+
+	return ret;
+}
+
+const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm = {
+	.extid_start = SBI_EXT_HSM,
+	.extid_end = SBI_EXT_HSM,
+	.handler = kvm_sbi_ext_hsm_handler,
+};