On 2019/10/13 17:02, Vitaly Kuznetsov wrote:
Zhenzhong Duan <zhenzhong.d...@oracle.com> writes:
...snip
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index ef836d6..6e14bd4 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -825,18 +825,31 @@ __visible bool __kvm_vcpu_is_preempted(long cpu)
*/
void __init kvm_spinlock_init(void)
{
- /* Does host kernel support KVM_FEATURE_PV_UNHALT? */
- if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT))
+ /*
+ * Disable PV qspinlocks if host kernel doesn't support
+ * KVM_FEATURE_PV_UNHALT feature or there is only 1 vCPU.
+ * virt_spin_lock_key is enabled to avoid lock holder
+ * preemption issue.
+ */
+ if (!kvm_para_has_feature(KVM_FEATURE_PV_UNHALT) ||
+ num_possible_cpus() == 1) {
+ pr_info("PV spinlocks disabled\n");
Why don't we need static_branch_disable(&virt_spin_lock_key) here?
Thanks for review.
I have a brief explanation in above comment area.
Boris also raised the same question in v4 and see my detailed explanation
in https://lkml.org/lkml/2019/10/6/39
Also, as you're printing the exact reason for PV spinlocks disablement
in other cases, I'd suggest separating "no host support" and "single
CPU" cases.
Will do after reaching a consensus on your first question.
return;
+ }
if (kvm_para_has_hint(KVM_HINTS_REALTIME)) {
+ pr_info("PV spinlocks disabled with KVM_HINTS_REALTIME
hints.\n");
static_branch_disable(&virt_spin_lock_key);
return;
}
- /* Don't use the pvqspinlock code if there is only 1 vCPU. */
- if (num_possible_cpus() == 1)
+ if (nopvspin) {
+ pr_info("PV spinlocks disabled forced by \"nopvspin\"
parameter.\n");
Nit: to make it sound better a comma is missing between 'disabled' and
'forced', or
"PV spinlocks forcefully disabled by ..." if you prefer.
Will do.
Zhenzhong
