iommu/vt-d: Check whether device requires bounce buffer

This adds a helper to check whether a device needs to
use bounce buffer. It also provides a boot time option
to disable the bounce buffer. Users can use this to
prevent the iommu driver from using the bounce buffer
for performance gain.

Cc: Ashok Raj <ashok.raj@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Tested-by: Xu Pengfei <pengfei.xu@intel.com>
Tested-by: Mika Westerberg <mika.westerberg@intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

2 files changed, 12 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 47d981a86e2f..aaca73080097 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1732,6 +1732,11 @@
                         Note that using this option lowers the security
                         provided by tboot because it makes the system
                         vulnerable to DMA attacks.
+                nobounce [Default off]
+                        Disable bounce buffer for unstrusted devices such as
+                        the Thunderbolt devices. This will treat the untrusted
+                        devices as the trusted ones, hence might expose security
+                        risks of DMA attacks.
 
         intel_idle.max_cstate=  [KNL,HW,ACPI,X86]
                         0       disables intel_idle and fall back on acpi_idle.
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index 12d094d08c0a..ce6baabc9dcc 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -360,6 +360,7 @@ static int dmar_forcedac;
 static int intel_iommu_strict;
 static int intel_iommu_superpage = 1;
 static int iommu_identity_mapping;
+static int intel_no_bounce;
 
 #define IDENTMAP_ALL            1
 #define IDENTMAP_GFX            2
@@ -373,6 +374,9 @@ EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped);
 static DEFINE_SPINLOCK(device_domain_lock);
 static LIST_HEAD(device_domain_list);
 
+#define device_needs_bounce(d) (!intel_no_bounce && dev_is_pci(d) &&    \
+                                to_pci_dev(d)->untrusted)
+
 /*
  * Iterate over elements in device_domain_list and call the specified
  * callback @fn against each element.
@@ -455,6 +459,9 @@ static int __init intel_iommu_setup(char *str)
                         printk(KERN_INFO
                                 "Intel-IOMMU: not forcing on after tboot. This could expose security risk for tboot\n");
                         intel_iommu_tboot_noforce = 1;
+                } else if (!strncmp(str, "nobounce", 8)) {
+                        pr_info("Intel-IOMMU: No bounce buffer. This could expose security risks of DMA attacks\n");
+                        intel_no_bounce = 1;
                 }
 
                 str += strcspn(str, ",");