linux-kernel - [PATCH 1/2] KVM: x86: reduce pvclock_gtod_sync

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Message-Id: <20210330165958.3094759-2-pbonzini@redhat.com>
Date:   Tue, 30 Mar 2021 12:59:57 -0400
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     mtosatti@...hat.com, vkuznets@...hat.com, dwmw@...zon.co.uk
Subject: [PATCH 1/2] KVM: x86: reduce pvclock_gtod_sync_lock critical sections

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 <dwmw@...zon.co.uk>
Cc: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.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