diff --git a/hypervisor/arch/x86/vtd.c b/hypervisor/arch/x86/vtd.c
index fea3ae6d9..a0d896634 100644
--- a/hypervisor/arch/x86/vtd.c
+++ b/hypervisor/arch/x86/vtd.c
@@ -952,6 +952,8 @@ static void dmar_enable_qi(struct dmar_drhd_rt *dmar_unit)
 {
 	uint32_t status = 0;
 
+	spinlock_obtain(&(dmar_unit->lock));
+
 	dmar_unit->qi_queue = hva2hpa(get_qi_queue(dmar_unit->index));
 	iommu_write64(dmar_unit, DMAR_IQA_REG, dmar_unit->qi_queue);
 
@@ -962,17 +964,23 @@ static void dmar_enable_qi(struct dmar_drhd_rt *dmar_unit)
 		iommu_write32(dmar_unit, DMAR_GCMD_REG,	dmar_unit->gcmd);
 		dmar_wait_completion(dmar_unit, DMAR_GSTS_REG, DMA_GSTS_QIES, false, &status);
 	}
+
+	spinlock_release(&(dmar_unit->lock));
 }
 
 static void dmar_disable_qi(struct dmar_drhd_rt *dmar_unit)
 {
 	uint32_t status = 0;
 
+	spinlock_obtain(&(dmar_unit->lock));
+
 	if ((dmar_unit->gcmd & DMA_GCMD_QIE) == DMA_GCMD_QIE) {
 		dmar_unit->gcmd &= ~DMA_GCMD_QIE;
 		iommu_write32(dmar_unit, DMAR_GCMD_REG,	dmar_unit->gcmd);
 		dmar_wait_completion(dmar_unit, DMAR_GSTS_REG, DMA_GSTS_QIES, true, &status);
 	}
+
+	spinlock_release(&(dmar_unit->lock));
 }
 
 static void dmar_prepare(struct dmar_drhd_rt *dmar_unit)