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    Subject[PATCH] kvm: Disable device assignment without interrupt remapping
    Date
    IOMMU interrupt remapping support provides a further layer of
    isolation for device assignment by preventing arbitrary interrupt
    block DMA writes by a malicious guest from reaching the host. By
    default, we should require that the platform provides interrupt
    remapping support, with an opt-in mechanism for existing behavior.

    Both AMD IOMMU and Intel VT-d2 hardware support interrupt
    remapping, however we currently only have software support on
    the Intel side. Users wishing to re-enable device assignment
    when interrupt remapping is not supported on the platform can
    use the "allow_unsafe_assigned_interrupts=1" module option.

    Signed-off-by: Alex Williamson <alex.williamson@redhat.com>
    ---

    virt/kvm/iommu.c | 15 +++++++++++++++
    1 files changed, 15 insertions(+), 0 deletions(-)

    diff --git a/virt/kvm/iommu.c b/virt/kvm/iommu.c
    index 62a9caf..243cb81 100644
    --- a/virt/kvm/iommu.c
    +++ b/virt/kvm/iommu.c
    @@ -30,6 +30,12 @@
    #include <linux/iommu.h>
    #include <linux/intel-iommu.h>

    +static int allow_unsafe_assigned_interrupts;
    +module_param_named(allow_unsafe_assigned_interrupts,
    + allow_unsafe_assigned_interrupts, bool, S_IRUGO | S_IWUSR);
    +MODULE_PARM_DESC(allow_unsafe_assigned_interrupts,
    + "Enable device assignment on platforms without interrupt remapping support.");
    +
    static int kvm_iommu_unmap_memslots(struct kvm *kvm);
    static void kvm_iommu_put_pages(struct kvm *kvm,
    gfn_t base_gfn, unsigned long npages);
    @@ -231,6 +237,15 @@ int kvm_iommu_map_guest(struct kvm *kvm)
    if (!kvm->arch.iommu_domain)
    return -ENOMEM;

    + if (!allow_unsafe_assigned_interrupts &&
    + !iommu_domain_has_cap(kvm->arch.iommu_domain,
    + IOMMU_CAP_INTR_REMAP)) {
    + printk(KERN_WARNING "%s: No interrupt remapping support, disallowing device assignment. Re-enble with \"allow_unsafe_assigned_interrupts=1\" module option.\n", __func__);
    + iommu_domain_free(kvm->arch.iommu_domain);
    + kvm->arch.iommu_domain = NULL;
    + return -EPERM;
    + }
    +
    r = kvm_iommu_map_memslots(kvm);
    if (r)
    goto out_unmap;


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