1 files changed, 135 insertions, 0 deletions
diff --git a/arch/riscv/kernel/paravirt.c b/arch/riscv/kernel/paravirt.c
new file mode 100644
index 000000000000..0d6225fd3194
--- /dev/null
+++ b/arch/riscv/kernel/paravirt.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Copyright (c) 2023 Ventana Micro Systems Inc.
+ */
+
+#define pr_fmt(fmt) "riscv-pv: " fmt
+
+#include <linux/cpuhotplug.h>
+#include <linux/compiler.h>
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/jump_label.h>
+#include <linux/kconfig.h>
+#include <linux/kernel.h>
+#include <linux/percpu-defs.h>
+#include <linux/printk.h>
+#include <linux/static_call.h>
+#include <linux/types.h>
+
+#include <asm/barrier.h>
+#include <asm/page.h>
+#include <asm/paravirt.h>
+#include <asm/sbi.h>
+
+struct static_key paravirt_steal_enabled;
+struct static_key paravirt_steal_rq_enabled;
+
+static u64 native_steal_clock(int cpu)
+{
+	return 0;
+}
+
+DEFINE_STATIC_CALL(pv_steal_clock, native_steal_clock);
+
+static bool steal_acc = true;
+static int __init parse_no_stealacc(char *arg)
+{
+	steal_acc = false;
+	return 0;
+}
+
+early_param("no-steal-acc", parse_no_stealacc);
+
+static DEFINE_PER_CPU(struct sbi_sta_struct, steal_time) __aligned(64);
+
+static bool __init has_pv_steal_clock(void)
+{
+	if (sbi_spec_version >= sbi_mk_version(2, 0) &&
+	    sbi_probe_extension(SBI_EXT_STA) > 0) {
+		pr_info("SBI STA extension detected\n");
+		return true;
+	}
+
+	return false;
+}
+
+static int sbi_sta_steal_time_set_shmem(unsigned long lo, unsigned long hi,
+					unsigned long flags)
+{
+	struct sbiret ret;
+
+	ret = sbi_ecall(SBI_EXT_STA, SBI_EXT_STA_STEAL_TIME_SET_SHMEM,
+			lo, hi, flags, 0, 0, 0);
+	if (ret.error) {
+		if (lo == SBI_STA_SHMEM_DISABLE && hi == SBI_STA_SHMEM_DISABLE)
+			pr_warn("Failed to disable steal-time shmem");
+		else
+			pr_warn("Failed to set steal-time shmem");
+		return sbi_err_map_linux_errno(ret.error);
+	}
+
+	return 0;
+}
+
+static int pv_time_cpu_online(unsigned int cpu)
+{
+	struct sbi_sta_struct *st = this_cpu_ptr(&steal_time);
+	phys_addr_t pa = __pa(st);
+	unsigned long lo = (unsigned long)pa;
+	unsigned long hi = IS_ENABLED(CONFIG_32BIT) ? upper_32_bits((u64)pa) : 0;
+
+	return sbi_sta_steal_time_set_shmem(lo, hi, 0);
+}
+
+static int pv_time_cpu_down_prepare(unsigned int cpu)
+{
+	return sbi_sta_steal_time_set_shmem(SBI_STA_SHMEM_DISABLE,
+					    SBI_STA_SHMEM_DISABLE, 0);
+}
+
+static u64 pv_time_steal_clock(int cpu)
+{
+	struct sbi_sta_struct *st = per_cpu_ptr(&steal_time, cpu);
+	__le32 sequence;
+	__le64 steal;
+
+	/*
+	 * Check the sequence field before and after reading the steal
+	 * field. Repeat the read if it is different or odd.
+	 */
+	do {
+		sequence = READ_ONCE(st->sequence);
+		virt_rmb();
+		steal = READ_ONCE(st->steal);
+		virt_rmb();
+	} while ((le32_to_cpu(sequence) & 1) ||
+		 sequence != READ_ONCE(st->sequence));
+
+	return le64_to_cpu(steal);
+}
+
+int __init pv_time_init(void)
+{
+	int ret;
+
+	if (!has_pv_steal_clock())
+		return 0;
+
+	ret = cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
+				"riscv/pv_time:online",
+				pv_time_cpu_online,
+				pv_time_cpu_down_prepare);
+	if (ret < 0)
+		return ret;
+
+	static_call_update(pv_steal_clock, pv_time_steal_clock);
+
+	static_key_slow_inc(&paravirt_steal_enabled);
+	if (steal_acc)
+		static_key_slow_inc(&paravirt_steal_rq_enabled);
+
+	pr_info("Computing paravirt steal-time\n");
+
+	return 0;
+}