Intel IOMMU Pass Through Support

The patch adds kernel parameter intel_iommu=pt to set up pass through
mode in context mapping entry. This disables DMAR in linux kernel; but
KVM still runs on VT-d and interrupt remapping still works.

In this mode, kernel uses swiotlb for DMA API functions but other VT-d
functionalities are enabled for KVM. KVM always uses multi level
translation page table in VT-d. By default, pass though mode is disabled
in kernel.

This is useful when people don't want to enable VT-d DMAR in kernel but
still want to use KVM and interrupt remapping for reasons like DMAR
performance concern or debug purpose.

Signed-off-by: Fenghua Yu <fenghua.yu@intel.com>
Acked-by: Weidong Han <weidong@intel.com>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

1 files changed, 10 insertions, 1 deletions

diff --git a/drivers/pci/dmar.c b/drivers/pci/dmar.c
index fa3a11365ec3..d3d86b749eee 100644
--- a/drivers/pci/dmar.c
+++ b/drivers/pci/dmar.c
@@ -515,6 +515,7 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
         u32 ver;
         static int iommu_allocated = 0;
         int agaw = 0;
+        int msagaw = 0;
 
         iommu = kzalloc(sizeof(*iommu), GFP_KERNEL);
         if (!iommu)
@@ -535,12 +536,20 @@ int alloc_iommu(struct dmar_drhd_unit *drhd)
         agaw = iommu_calculate_agaw(iommu);
         if (agaw < 0) {
                 printk(KERN_ERR
-                        "Cannot get a valid agaw for iommu (seq_id = %d)\n",
+                       "Cannot get a valid agaw for iommu (seq_id = %d)\n",
+                       iommu->seq_id);
+                goto error;
+        }
+        msagaw = iommu_calculate_max_sagaw(iommu);
+        if (msagaw < 0) {
+                printk(KERN_ERR
+                        "Cannot get a valid max agaw for iommu (seq_id = %d)\n",
                         iommu->seq_id);
                 goto error;
         }
 #endif
         iommu->agaw = agaw;
+        iommu->msagaw = msagaw;
 
         /* the registers might be more than one page */
         map_size = max_t(int, ecap_max_iotlb_offset(iommu->ecap),