[PATCH v3 7/7] KVM: VMX: optimize ple_window updates to VMCS

[Radim Krčmář <rkrcmar@xxxxxxxxxx>]

ple_window is preserved in VMCS, so can write it only after a change.
Do this by keeping a dirty bit.

Signed-off-by: Radim Krčmář <rkrcmar@xxxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1318232..f32415b 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -510,6 +510,7 @@ struct vcpu_vmx {
 
 	/* Dynamic PLE window. */
 	int ple_window;
+	bool ple_window_dirty;
 };
 
 enum segment_cache_field {
@@ -4426,6 +4427,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
 		vmcs_write64(POSTED_INTR_DESC_ADDR, __pa((&vmx->pi_desc)));
 	}
 
+	vmx->ple_window_dirty = ple_gap;
 	if (ple_gap) {
 		vmcs_write32(PLE_GAP, ple_gap);
 		vmx->ple_window = ple_window;
@@ -5741,6 +5743,9 @@ static void grow_ple_window(struct kvm_vcpu *vcpu)
 		vmx->ple_window = __grow_ple_window(old);
 	} while (read_seqretry(&ple_window_seqlock, seq));
 
+	if (vmx->ple_window != old)
+		vmx->ple_window_dirty = true;
+
 	trace_kvm_ple_window_grow(vcpu->vcpu_id, vmx->ple_window, old);
 }
 
@@ -5756,6 +5761,9 @@ static void shrink_ple_window(struct kvm_vcpu *vcpu)
 		                                      ple_window);
 	} while (read_seqretry(&ple_window_seqlock, seq));
 
+	if (vmx->ple_window != old)
+		vmx->ple_window_dirty = true;
+
 	trace_kvm_ple_window_shrink(vcpu->vcpu_id, vmx->ple_window, old);
 }
 
@@ -7505,8 +7513,10 @@ static void __noclone vmx_vcpu_run(struct kvm_vcpu *vcpu)
 	if (vmx->emulation_required)
 		return;
 
-	if (ple_gap)
+	if (vmx->ple_window_dirty) {
+		vmx->ple_window_dirty = false;
 		vmcs_write32(PLE_WINDOW, vmx->ple_window);
+	}
 
 	if (vmx->nested.sync_shadow_vmcs) {
 		copy_vmcs12_to_shadow(vmx);
-- 
2.1.0

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