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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>
This commit is contained in:
Lu Baolu 2019-09-06 14:14:49 +08:00 committed by Joerg Roedel
parent 3fc1ca0065
commit e5e04d0519
2 changed files with 12 additions and 0 deletions
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5
Documentation/admin-guide/kernel-parameters.txt
View File

@ -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.

7
drivers/iommu/intel-iommu.c
View File

@ -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, ",");