iommu/vt-d: Fix NULL pointer reference in intel_svm_bind_mm()

mainline inclusion
from mainline-5.1-rc1
commit c56cba5daf45d2d091ef1cfe2f1d6a930446687b
category: bugfix
bugzilla: NA
CVE: NA

-------------------------------------------------
Intel IOMMU could be turned off with intel_iommu=off. If Intel
IOMMU is off,  the intel_iommu struct will not be initialized.
When device drivers call intel_svm_bind_mm(), the NULL pointer
reference will happen there.

Add dmar_disabled check to avoid NULL pointer reference.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Reported-by: NDave Jiang <dave.jiang@intel.com>
Fixes: 2f26e0a9 ("iommu/vt-d: Add basic SVM PASID support")
Signed-off-by: NLu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: NJoerg Roedel <jroedel@suse.de>
(cherry picked from commit c56cba5daf45d2d091ef1cfe2f1d6a930446687b)
Signed-off-by: NZhen Lei <thunder.leizhen@huawei.com>
Reviewed-by: NYang Yingliang <yangyingliang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

drivers/iommu/intel-svm.c

@@ -293,7 +293,7 @@ int intel_svm_bind_mm(struct device *dev, int *pasid, int flags, struct svm_dev_
 	int pasid_max;
 	int ret;
 
-	if (!iommu)
+	if (!iommu || dmar_disabled)
 		return -EINVAL;
 
 	if (dev_is_pci(dev)) {