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    Subject[PATCH v3 08/10] iommu/vt-d: Check whether device requires bounce buffer
    Date
    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>
    ---
    Documentation/admin-guide/kernel-parameters.txt | 5 +++++
    drivers/iommu/intel-iommu.c | 17 +++++++++++++++++
    2 files changed, 22 insertions(+)

    diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
    index 2b8ee90bb644..86880eb3fc73 100644
    --- a/Documentation/admin-guide/kernel-parameters.txt
    +++ b/Documentation/admin-guide/kernel-parameters.txt
    @@ -1726,6 +1726,11 @@
    Note that using this option lowers the security
    provided by tboot because it makes the system
    vulnerable to DMA attacks.
    + nobounce [Default off]
    + Do not use the bounce buffer for untrusted devices like
    + 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 e4a164324bdd..0d80f26b8a72 100644
    --- a/drivers/iommu/intel-iommu.c
    +++ b/drivers/iommu/intel-iommu.c
    @@ -380,6 +380,7 @@ static int intel_iommu_strict;
    static int intel_iommu_superpage = 1;
    static int intel_iommu_sm;
    static int iommu_identity_mapping;
    +static int intel_no_bounce;

    #define IDENTMAP_ALL 1
    #define IDENTMAP_GFX 2
    @@ -396,6 +397,19 @@ EXPORT_SYMBOL_GPL(intel_iommu_gfx_mapped);
    static DEFINE_SPINLOCK(device_domain_lock);
    static LIST_HEAD(device_domain_list);

    +static inline bool device_needs_bounce(struct device *dev)
    +{
    + struct pci_dev *pdev = NULL;
    +
    + if (intel_no_bounce)
    + return false;
    +
    + if (dev_is_pci(dev))
    + pdev = to_pci_dev(dev);
    +
    + return pdev ? pdev->untrusted : false;
    +}
    +
    /*
    * Iterate over elements in device_domain_list and call the specified
    * callback @fn against each element.
    @@ -478,6 +492,9 @@ 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, ",");
    --
    2.17.1
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