Commit e5e04d05 authored by Lu Baolu's avatar Lu Baolu Committed by Joerg Roedel
Browse files

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: default avatarLu Baolu <baolu.lu@linux.intel.com>
Tested-by: default avatarXu Pengfei <pengfei.xu@intel.com>
Tested-by: default avatarMika Westerberg <mika.westerberg@intel.com>
Signed-off-by: default avatarJoerg Roedel <jroedel@suse.de>
parent 3fc1ca00

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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.

drivers/iommu/intel-iommu.c

+7 −0
Original line number Diff line number Diff line
@@ -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, ",");

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