[PATCH 1/2] KVM: x86: reduce pvclock_gtod_sync_lock critical sections

[Paolo Bonzini]

There is no need to include changes to vcpu->requests into
the pvclock_gtod_sync_lock critical section.  The changes to
the shared data structures (in pvclock_update_vm_gtod_copy)
already occur under the lock.

Cc: David Woodhouse <d...@amazon.co.uk>
Cc: Marcelo Tosatti <mtosa...@redhat.com>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
---
 arch/x86/kvm/x86.c | 10 ++++------
 1 file changed, 4 insertions(+), 6 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index fe806e894212..0a83eff40b43 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2562,10 +2562,12 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
 
        kvm_hv_invalidate_tsc_page(kvm);
 
-       spin_lock(&ka->pvclock_gtod_sync_lock);
        kvm_make_mclock_inprogress_request(kvm);
+
        /* no guest entries from this point */
+       spin_lock(&ka->pvclock_gtod_sync_lock);
        pvclock_update_vm_gtod_copy(kvm);
+       spin_unlock(&ka->pvclock_gtod_sync_lock);
 
        kvm_for_each_vcpu(i, vcpu, kvm)
                kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
@@ -2573,8 +2575,6 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)
        /* guest entries allowed */
        kvm_for_each_vcpu(i, vcpu, kvm)
                kvm_clear_request(KVM_REQ_MCLOCK_INPROGRESS, vcpu);
-
-       spin_unlock(&ka->pvclock_gtod_sync_lock);
 #endif
 }
 
@@ -7740,16 +7740,14 @@ static void kvm_hyperv_tsc_notifier(void)
                struct kvm_arch *ka = &kvm->arch;
 
                spin_lock(&ka->pvclock_gtod_sync_lock);
-
                pvclock_update_vm_gtod_copy(kvm);
+               spin_unlock(&ka->pvclock_gtod_sync_lock);
 
                kvm_for_each_vcpu(cpu, vcpu, kvm)
                        kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu);
 
                kvm_for_each_vcpu(cpu, vcpu, kvm)
                        kvm_clear_request(KVM_REQ_MCLOCK_INPROGRESS, vcpu);
-
-               spin_unlock(&ka->pvclock_gtod_sync_lock);
        }
        mutex_unlock(&kvm_lock);
 }
-- 
2.26.2