Commit f85f6e7b authored by Wanpeng Li's avatar Wanpeng Li Committed by Paolo Bonzini
Browse files

KVM: X86: Yield to IPI target if necessary 



When sending a call-function IPI-many to vCPUs, yield if any of
the IPI target vCPUs was preempted, we just select the first
preempted target vCPU which we found since the state of target
vCPUs can change underneath and to avoid race conditions.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Liran Alon <liran.alon@oracle.com>
Signed-off-by: default avatarWanpeng Li <wanpengli@tencent.com>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 11e34914

Documentation/virtual/kvm/hypercalls.txt

+11 −0
Original line number Diff line number Diff line
@@ -141,3 +141,14 @@ a0 corresponds to the APIC ID in the third argument (a2), bit 1 
corresponds to the APIC ID a2+1, and so on.



Returns the number of CPUs to which the IPIs were delivered successfully.



7. KVM_HC_SCHED_YIELD

------------------------

Architecture: x86

Status: active

Purpose: Hypercall used to yield if the IPI target vCPU is preempted



a0: destination APIC ID



Usage example: When sending a call-function IPI-many to vCPUs, yield if

any of the IPI target vCPUs was preempted.

arch/x86/include/uapi/asm/kvm_para.h

+1 −0
Original line number Diff line number Diff line
@@ -30,6 +30,7 @@ 
#define KVM_FEATURE_ASYNC_PF_VMEXIT	10

#define KVM_FEATURE_PV_SEND_IPI	11

#define KVM_FEATURE_POLL_CONTROL	12

#define KVM_FEATURE_PV_SCHED_YIELD	13



#define KVM_HINTS_REALTIME      0

arch/x86/kernel/kvm.c

+21 −0
Original line number Diff line number Diff line
@@ -527,6 +527,21 @@ static void kvm_setup_pv_ipi(void) 
	pr_info("KVM setup pv IPIs\n");

}



static void kvm_smp_send_call_func_ipi(const struct cpumask *mask)

{

	int cpu;



	native_send_call_func_ipi(mask);



	/* Make sure other vCPUs get a chance to run if they need to. */

	for_each_cpu(cpu, mask) {

		if (vcpu_is_preempted(cpu)) {

			kvm_hypercall1(KVM_HC_SCHED_YIELD, per_cpu(x86_cpu_to_apicid, cpu));

			break;

		}

	}

}



static void __init kvm_smp_prepare_cpus(unsigned int max_cpus)

{

	native_smp_prepare_cpus(max_cpus);
@@ -638,6 +653,12 @@ static void __init kvm_guest_init(void) 
#ifdef CONFIG_SMP

	smp_ops.smp_prepare_cpus = kvm_smp_prepare_cpus;

	smp_ops.smp_prepare_boot_cpu = kvm_smp_prepare_boot_cpu;

	if (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&

	    !kvm_para_has_hint(KVM_HINTS_REALTIME) &&

	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {

		smp_ops.send_call_func_ipi = kvm_smp_send_call_func_ipi;

		pr_info("KVM setup pv sched yield\n");

	}

	if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/kvm:online",

				      kvm_cpu_online, kvm_cpu_down_prepare) < 0)

		pr_err("kvm_guest: Failed to install cpu hotplug callbacks\n");

include/uapi/linux/kvm_para.h

+1 −0
Original line number Diff line number Diff line
@@ -28,6 +28,7 @@ 
#define KVM_HC_MIPS_CONSOLE_OUTPUT	8

#define KVM_HC_CLOCK_PAIRING		9

#define KVM_HC_SEND_IPI		10

#define KVM_HC_SCHED_YIELD		11



/*

 * hypercalls use architecture specific

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