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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: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Vitaly 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: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Zhenzhong Duan 2019-10-23 19:16:22 +08:00 committed by Paolo Bonzini
parent 5aefd786fb
commit 05eee619ed
4 changed files with 47 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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>]]]

1
arch/x86/include/asm/qspinlock.h
View File

@ -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
/**

43
arch/x86/kernel/kvm.c
View File

@ -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))
return;
if (kvm_para_has_hint(KVM_HINTS_REALTIME)) {
static_branch_disable(&virt_spin_lock_key);
/*
* 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;
}
/* Don't use the pvqspinlock code if there is only 1 vCPU. */
if (num_possible_cpus() == 1)
return;
/*
* Disable PV spinlocks and use native qspinlock when dedicated pCPUs
* are available.
*/
if (kvm_para_has_hint(KVM_HINTS_REALTIME)) {
pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME hints\n");
goto out;
}
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 */

7
kernel/locking/qspinlock.c
View File

@ -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