amd-iommu: disable cmd buffer and evt logging before reprogramming iommu

The IOMMU spec states that IOMMU behavior may be undefined when the
IOMMU registers are rewritten while command or event buffer is enabled.
Disable them in IOMMU disable path.
Signed-off-by: Chris Wright <chrisw@sous-sol.org>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

arch/x86/kernel/amd_iommu_init.c

@@ -260,6 +260,14 @@ static void iommu_enable(struct amd_iommu *iommu)
 
 static void iommu_disable(struct amd_iommu *iommu)
 {
+	/* Disable command buffer */
+	iommu_feature_disable(iommu, CONTROL_CMDBUF_EN);
+
+	/* Disable event logging and event interrupts */
+	iommu_feature_disable(iommu, CONTROL_EVT_INT_EN);
+	iommu_feature_disable(iommu, CONTROL_EVT_LOG_EN);
+
+	/* Disable IOMMU hardware itself */
 	iommu_feature_disable(iommu, CONTROL_IOMMU_EN);
 }
 
@@ -1042,6 +1050,7 @@ static void enable_iommus(void)
 	struct amd_iommu *iommu;
 
 	for_each_iommu(iommu) {
+		iommu_disable(iommu);
 		iommu_set_device_table(iommu);
 		iommu_enable_command_buffer(iommu);
 		iommu_enable_event_buffer(iommu);