Commit 05eee619 authored by Zhenzhong Duan's avatar Zhenzhong Duan Committed by Paolo Bonzini
Browse files

x86/kvm: Add "nopvspin" parameter to disable PV spinlocks 



There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" on XEN platform and
"hv_nopvspin" on HYPER_V).

That feature is missed on KVM, add a new parameter "nopvspin" to disable
PV spinlocks for KVM guest.

The new 'nopvspin' parameter will also replace Xen and Hyper-V specific
parameters in future patches.

Define variable nopvsin as global because it will be used in future
patches as above.

Signed-off-by: default avatarZhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
parent 5aefd786

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -5739,6 +5739,11 @@ 
			as generic guest with no PV drivers. Currently support

			XEN HVM, KVM, HYPER_V and VMWARE guest.



	nopvspin	[X86,KVM]

			Disables the qspinlock slow path using PV optimizations

			which allow the hypervisor to 'idle' the guest on lock

			contention.



	xirc2ps_cs=	[NET,PCMCIA]

			Format:

			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]

arch/x86/include/asm/qspinlock.h

+1 −0
Original line number Diff line number Diff line
@@ -32,6 +32,7 @@ extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); 
extern void __pv_init_lock_hash(void);

extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);

extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);

extern bool nopvspin;



#define	queued_spin_unlock queued_spin_unlock

/**

arch/x86/kernel/kvm.c

+32 −7
Original line number Diff line number Diff line
@@ -871,18 +871,36 @@ asm( 
 */

void __init kvm_spinlock_init(void)

{

	/* Does host kernel support KVM_FEATURE_PV_UNHALT? */

	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))

	/*

	 * In case host doesn't support KVM_FEATURE_PV_UNHALT there is still an

	 * advantage of keeping virt_spin_lock_key enabled: virt_spin_lock() is

	 * preferred over native qspinlock when vCPU is preempted.

	 */

	if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT)) {

		pr_info("PV spinlocks disabled, no host support\n");

		return;

	}



	/*

	 * Disable PV spinlocks and use native qspinlock when dedicated pCPUs

	 * are available.

	 */

	if (kvm_para_has_hint(KVM_HINTS_REALTIME)) {

		static_branch_disable(&virt_spin_lock_key);

		return;

		pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints\n");

		goto out;

	}



	/* Don't use the pvqspinlock code if there is only 1 vCPU. */

	if (num_possible_cpus() == 1)

		return;

	if (num_possible_cpus() == 1) {

		pr_info("PV spinlocks disabled, single CPU\n");

		goto out;

	}



	if (nopvspin) {

		pr_info("PV spinlocks disabled, forced by \"nopvspin\" parameter\n");

		goto out;

	}



	pr_info("PV spinlocks enabled\n");



	__pv_init_lock_hash();

	pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
@@ -895,6 +913,13 @@ void __init kvm_spinlock_init(void) 
		pv_ops.lock.vcpu_is_preempted =

			PV_CALLEE_SAVE(__kvm_vcpu_is_preempted);

	}

	/*

	 * When PV spinlock is enabled which is preferred over

	 * virt_spin_lock(), virt_spin_lock_key's value is meaningless.

	 * Just disable it anyway.

	 */

out:

	static_branch_disable(&virt_spin_lock_key);

}



#endif	/* CONFIG_PARAVIRT_SPINLOCKS */

kernel/locking/qspinlock.c

+7 −0
Original line number Diff line number Diff line
@@ -581,4 +581,11 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath); 
#include "qspinlock_paravirt.h"

#include "qspinlock.c"



bool nopvspin __initdata;

static __init int parse_nopvspin(char *arg)

{

	nopvspin = true;

	return 0;

}

early_param("nopvspin", parse_nopvspin);

#endif