Commit e0685fa2 authored by Steven Price's avatar Steven Price Committed by Marc Zyngier
Browse files

arm64: Retrieve stolen time as paravirtualized guest 



Enable paravirtualization features when running under a hypervisor
supporting the PV_TIME_ST hypercall.

For each (v)CPU, we ask the hypervisor for the location of a shared
page which the hypervisor will use to report stolen time to us. We set
pv_time_ops to the stolen time function which simply reads the stolen
value from the shared page for a VCPU. We guarantee single-copy
atomicity using READ_ONCE which means we can also read the stolen
time for another VCPU than the currently running one while it is
potentially being updated by the hypervisor.

Signed-off-by: default avatarSteven Price <steven.price@arm.com>
Signed-off-by: default avatarMarc Zyngier <maz@kernel.org>
parent ce4d5ca2

Documentation/admin-guide/kernel-parameters.txt

+3 −3
Original line number Diff line number Diff line
@@ -3083,9 +3083,9 @@ 
			[X86,PV_OPS] Disable paravirtualized VMware scheduler

			clock and use the default one.



	no-steal-acc	[X86,KVM] Disable paravirtualized steal time accounting.

			steal time is computed, but won't influence scheduler

			behaviour

	no-steal-acc	[X86,KVM,ARM64] Disable paravirtualized steal time

			accounting. steal time is computed, but won't

			influence scheduler behaviour



	nolapic		[X86-32,APIC] Do not enable or use the local APIC.

arch/arm64/include/asm/paravirt.h

+8 −1
Original line number Diff line number Diff line
@@ -21,6 +21,13 @@ static inline u64 paravirt_steal_clock(int cpu) 
{

	return pv_ops.time.steal_clock(cpu);

}

#endif



int __init pv_time_init(void);



#else



#define pv_time_init() do {} while (0)



#endif // CONFIG_PARAVIRT



#endif

arch/arm64/kernel/paravirt.c

+140 −0
Original line number Diff line number Diff line
@@ -6,13 +6,153 @@ 
 * Author: Stefano Stabellini <stefano.stabellini@eu.citrix.com>

 */



#define pr_fmt(fmt) "arm-pv: " fmt



#include <linux/arm-smccc.h>

#include <linux/cpuhotplug.h>

#include <linux/export.h>

#include <linux/io.h>

#include <linux/jump_label.h>

#include <linux/printk.h>

#include <linux/psci.h>

#include <linux/reboot.h>

#include <linux/slab.h>

#include <linux/types.h>



#include <asm/paravirt.h>

#include <asm/pvclock-abi.h>

#include <asm/smp_plat.h>



struct static_key paravirt_steal_enabled;

struct static_key paravirt_steal_rq_enabled;



struct paravirt_patch_template pv_ops;

EXPORT_SYMBOL_GPL(pv_ops);



struct pv_time_stolen_time_region {

	struct pvclock_vcpu_stolen_time *kaddr;

};



static DEFINE_PER_CPU(struct pv_time_stolen_time_region, stolen_time_region);



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);



/* return stolen time in ns by asking the hypervisor */

static u64 pv_steal_clock(int cpu)

{

	struct pv_time_stolen_time_region *reg;



	reg = per_cpu_ptr(&stolen_time_region, cpu);

	if (!reg->kaddr) {

		pr_warn_once("stolen time enabled but not configured for cpu %d\n",

			     cpu);

		return 0;

	}



	return le64_to_cpu(READ_ONCE(reg->kaddr->stolen_time));

}



static int stolen_time_dying_cpu(unsigned int cpu)

{

	struct pv_time_stolen_time_region *reg;



	reg = this_cpu_ptr(&stolen_time_region);

	if (!reg->kaddr)

		return 0;



	memunmap(reg->kaddr);

	memset(reg, 0, sizeof(*reg));



	return 0;

}



static int init_stolen_time_cpu(unsigned int cpu)

{

	struct pv_time_stolen_time_region *reg;

	struct arm_smccc_res res;



	reg = this_cpu_ptr(&stolen_time_region);



	arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_ST, &res);



	if (res.a0 == SMCCC_RET_NOT_SUPPORTED)

		return -EINVAL;



	reg->kaddr = memremap(res.a0,

			      sizeof(struct pvclock_vcpu_stolen_time),

			      MEMREMAP_WB);



	if (!reg->kaddr) {

		pr_warn("Failed to map stolen time data structure\n");

		return -ENOMEM;

	}



	if (le32_to_cpu(reg->kaddr->revision) != 0 ||

	    le32_to_cpu(reg->kaddr->attributes) != 0) {

		pr_warn_once("Unexpected revision or attributes in stolen time data\n");

		return -ENXIO;

	}



	return 0;

}



static int pv_time_init_stolen_time(void)

{

	int ret;



	ret = cpuhp_setup_state(CPUHP_AP_ARM_KVMPV_STARTING,

				"hypervisor/arm/pvtime:starting",

				init_stolen_time_cpu, stolen_time_dying_cpu);

	if (ret < 0)

		return ret;

	return 0;

}



static bool has_pv_steal_clock(void)

{

	struct arm_smccc_res res;



	/* To detect the presence of PV time support we require SMCCC 1.1+ */

	if (psci_ops.smccc_version < SMCCC_VERSION_1_1)

		return false;



	arm_smccc_1_1_invoke(ARM_SMCCC_ARCH_FEATURES_FUNC_ID,

			     ARM_SMCCC_HV_PV_TIME_FEATURES, &res);



	if (res.a0 != SMCCC_RET_SUCCESS)

		return false;



	arm_smccc_1_1_invoke(ARM_SMCCC_HV_PV_TIME_FEATURES,

			     ARM_SMCCC_HV_PV_TIME_ST, &res);



	return (res.a0 == SMCCC_RET_SUCCESS);

}



int __init pv_time_init(void)

{

	int ret;



	if (!has_pv_steal_clock())

		return 0;



	ret = pv_time_init_stolen_time();

	if (ret)

		return ret;



	pv_ops.time.steal_clock = pv_steal_clock;



	static_key_slow_inc(&paravirt_steal_enabled);

	if (steal_acc)

		static_key_slow_inc(&paravirt_steal_rq_enabled);



	pr_info("using stolen time PV\n");



	return 0;

}

arch/arm64/kernel/time.c

+3 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 


#include <asm/thread_info.h>

#include <asm/stacktrace.h>

#include <asm/paravirt.h>



unsigned long profile_pc(struct pt_regs *regs)

{
@@ -65,4 +66,6 @@ void __init time_init(void) 


	/* Calibrate the delay loop directly */

	lpj_fine = arch_timer_rate / HZ;



	pv_time_init();

}

include/linux/cpuhotplug.h

+1 −0
Original line number Diff line number Diff line
@@ -136,6 +136,7 @@ enum cpuhp_state { 
	/* Must be the last timer callback */

	CPUHP_AP_DUMMY_TIMER_STARTING,

	CPUHP_AP_ARM_XEN_STARTING,

	CPUHP_AP_ARM_KVMPV_STARTING,

	CPUHP_AP_ARM_CORESIGHT_STARTING,

	CPUHP_AP_ARM64_ISNDEP_STARTING,

	CPUHP_AP_SMPCFD_DYING,

CRA Git | Maintained and supported by SUSTech CRA and CCSE