On Wed, 20 Dec 2023 08:00:16 PST (-0800), ajones@xxxxxxxxxxxxxxxx wrote:
When the SBI STA extension exists we can use it to implement
paravirt steal-time support. Fill in the empty pv-time functions
with an SBI STA implementation and add the Kconfig knobs allowing
it to be enabled.
Reviewed-by: Atish Patra <atishp@xxxxxxxxxxxx>
Reviewed-by: Anup Patel <anup@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Jones <ajones@xxxxxxxxxxxxxxxx>
---
arch/riscv/Kconfig | 19 +++++++++++
arch/riscv/kernel/paravirt.c | 63 ++++++++++++++++++++++++++++++++++--
2 files changed, 79 insertions(+), 3 deletions(-)
diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 95a2a06acc6a..b99fd8129edf 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -724,6 +724,25 @@ config COMPAT
If you want to execute 32-bit userspace applications, say Y.
+config PARAVIRT
+ bool "Enable paravirtualization code"
+ depends on RISCV_SBI
+ help
+ This changes the kernel so it can modify itself when it is run
+ under a hypervisor, potentially improving performance significantly
+ over full virtualization.
+
+config PARAVIRT_TIME_ACCOUNTING
+ bool "Paravirtual steal time accounting"
+ depends on PARAVIRT
+ help
+ Select this option to enable fine granularity task steal time
+ accounting. Time spent executing other tasks in parallel with
+ the current vCPU is discounted from the vCPU power. To account for
+ that, there can be a small performance impact.
+
+ If in doubt, say N here.
+
config RELOCATABLE
bool "Build a relocatable kernel"
depends on MMU && 64BIT && !XIP_KERNEL
diff --git a/arch/riscv/kernel/paravirt.c b/arch/riscv/kernel/paravirt.c
index 080c95d2a295..574733b2bbea 100644
--- a/arch/riscv/kernel/paravirt.c
+++ b/arch/riscv/kernel/paravirt.c
@@ -6,12 +6,21 @@
#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/sbi.h>
+
struct static_key paravirt_steal_enabled;
struct static_key paravirt_steal_rq_enabled;
@@ -31,24 +40,72 @@ static int __init parse_no_stealacc(char *arg)
early_param("no-steal-acc", parse_no_stealacc);
+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 pv_time_cpu_online(unsigned int cpu)
+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 0;
+ return sbi_sta_steal_time_set_shmem(SBI_STA_SHMEM_DISABLE,
+ SBI_STA_SHMEM_DISABLE, 0);
}
static u64 pv_time_steal_clock(int cpu)
{
- return 0;
+ struct sbi_sta_struct *st = per_cpu_ptr(&steal_time, cpu);
+ u32 sequence;
+ u64 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)
Acked-by: Palmer Dabbelt <palmer@xxxxxxxxxxxx>
