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Subject[PATCH v2 5/6] RISC-V: Add SBI HSM extension in KVM
Date
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>
---
arch/riscv/include/asm/sbi.h | 1 +
arch/riscv/kvm/Makefile | 2 +-
arch/riscv/kvm/vcpu.c | 19 ++++++
arch/riscv/kvm/vcpu_sbi.c | 4 ++
arch/riscv/kvm/vcpu_sbi_hsm.c | 109 ++++++++++++++++++++++++++++++++++
5 files changed, 134 insertions(+), 1 deletion(-)
create mode 100644 arch/riscv/kvm/vcpu_sbi_hsm.c

diff --git a/arch/riscv/include/asm/sbi.h b/arch/riscv/include/asm/sbi.h
index 4a405f583d32..881e89078785 100644
--- a/arch/riscv/include/asm/sbi.h
+++ b/arch/riscv/include/asm/sbi.h
@@ -106,6 +106,7 @@ enum sbi_srst_reset_reason {
#define SBI_ERR_INVALID_PARAM -3
#define SBI_ERR_DENIED -4
#define SBI_ERR_INVALID_ADDRESS -5
+#define SBI_ERR_ALREADY_AVAILABLE -6

extern unsigned long sbi_spec_version;
struct sbiret {
diff --git a/arch/riscv/kvm/Makefile b/arch/riscv/kvm/Makefile
index 302501295397..5627c9c7f249 100644
--- a/arch/riscv/kvm/Makefile
+++ b/arch/riscv/kvm/Makefile
@@ -11,5 +11,5 @@ kvm-objs := $(common-objs-y)

kvm-objs += main.o vm.o vmid.o tlb.o mmu.o
kvm-objs += vcpu.o vcpu_exit.o vcpu_switch.o vcpu_timer.o
-kvm-objs += vcpu_sbi.o vcpu_sbi_base.o vcpu_sbi_legacy.o vcpu_sbi_replace.o
+kvm-objs += vcpu_sbi.o vcpu_sbi_base.o vcpu_sbi_legacy.o vcpu_sbi_replace.o vcpu_sbi_hsm.o
obj-$(CONFIG_KVM) += kvm.o
diff --git a/arch/riscv/kvm/vcpu.c b/arch/riscv/kvm/vcpu.c
index bcc4af9d2fa9..99f94ab27cea 100644
--- a/arch/riscv/kvm/vcpu.c
+++ b/arch/riscv/kvm/vcpu.c
@@ -130,6 +130,13 @@ static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)
struct kvm_vcpu_csr *reset_csr = &vcpu->arch.guest_reset_csr;
struct kvm_cpu_context *cntx = &vcpu->arch.guest_context;
struct kvm_cpu_context *reset_cntx = &vcpu->arch.guest_reset_context;
+ bool loaded;
+
+ /* Disable preemption to avoid race with preempt notifiers */
+ preempt_disable();
+ loaded = (vcpu->cpu != -1);
+ if (loaded)
+ kvm_arch_vcpu_put(vcpu);

memcpy(csr, reset_csr, sizeof(*csr));

@@ -141,6 +148,11 @@ static void kvm_riscv_reset_vcpu(struct kvm_vcpu *vcpu)

WRITE_ONCE(vcpu->arch.irqs_pending, 0);
WRITE_ONCE(vcpu->arch.irqs_pending_mask, 0);
+
+ /* Reset the guest CSRs for hotplug usecase */
+ if (loaded)
+ kvm_arch_vcpu_load(vcpu, smp_processor_id());
+ preempt_enable();
}

int kvm_arch_vcpu_precreate(struct kvm *kvm, unsigned int id)
@@ -182,6 +194,13 @@ int kvm_arch_vcpu_setup(struct kvm_vcpu *vcpu)

void kvm_arch_vcpu_postcreate(struct kvm_vcpu *vcpu)
{
+ /**
+ * vcpu with id 0 is the designated boot cpu.
+ * Keep all vcpus with non-zero cpu id in power-off state so that they
+ * can brought to online using SBI HSM extension.
+ */
+ if (vcpu->vcpu_idx != 0)
+ kvm_riscv_vcpu_power_off(vcpu);
}

void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
diff --git a/arch/riscv/kvm/vcpu_sbi.c b/arch/riscv/kvm/vcpu_sbi.c
index e21ce1e69e03..20ef59ed83a6 100644
--- a/arch/riscv/kvm/vcpu_sbi.c
+++ b/arch/riscv/kvm/vcpu_sbi.c
@@ -25,6 +25,8 @@ static int kvm_linux_err_map_sbi(int err)
return SBI_ERR_INVALID_ADDRESS;
case -EOPNOTSUPP:
return SBI_ERR_NOT_SUPPORTED;
+ case -EALREADY:
+ return SBI_ERR_ALREADY_AVAILABLE;
default:
return SBI_ERR_FAILURE;
};
@@ -35,6 +37,7 @@ extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_base;
extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_time;
extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_ipi;
extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_rfence;
+extern const struct kvm_vcpu_sbi_extension vcpu_sbi_ext_hsm;

static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
&vcpu_sbi_ext_legacy,
@@ -42,6 +45,7 @@ static const struct kvm_vcpu_sbi_extension *sbi_ext[] = {
&vcpu_sbi_ext_time,
&vcpu_sbi_ext_ipi,
&vcpu_sbi_ext_rfence,
+ &vcpu_sbi_ext_hsm,
};

void kvm_riscv_vcpu_sbi_forward(struct kvm_vcpu *vcpu, struct kvm_run *run)
diff --git a/arch/riscv/kvm/vcpu_sbi_hsm.c b/arch/riscv/kvm/vcpu_sbi_hsm.c
new file mode 100644
index 000000000000..ce6cfe125559
--- /dev/null
+++ b/arch/riscv/kvm/vcpu_sbi_hsm.c
@@ -0,0 +1,109 @@
+// SPDX-License-Identifier: GPL-2.0
+/**
+ * Copyright (c) 2020 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);
+
+ /* Make sure that the reset request is enqueued before power on */
+ smp_wmb();
+ kvm_riscv_vcpu_power_on(target_vcpu);
+
+ return 0;
+}
+
+static int kvm_sbi_hsm_vcpu_stop(struct kvm_vcpu *vcpu)
+{
+ if ((!vcpu) || (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;
+
+ if (!cp)
+ return -EINVAL;
+ 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,
+};
--
2.25.1
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