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    Subject[PATCH v3] irq_remap: disable IRQ remapping if any IOAPIC lacks an IOMMU
    Date
    The ACPI tables in the Macbook Air 5,1 define a single IOAPIC with id 2,
    but the only remapping unit described in the DMAR table matches id 0.
    Interrupt remapping fails as a result, and the kernel panics with the
    message "timer doesn't work through Interrupt-remapped IO-APIC."

    To fix this, check each IOAPIC for a corresponding IOMMU. If an IOMMU is
    not found, do not allow IRQ remapping to be enabled.

    v2: Move check to parse_ioapics_under_ir(), raise log level to KERN_ERR,
    and add FW_BUG to the log message
    v3: Skip check if IOMMU doesn't support interrupt remapping and remove
    existing check that the IOMMU count equals the IOAPIC count

    Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>
    Signed-off-by: Seth Forshee <seth.forshee@canonical.com>
    ---
    drivers/iommu/intel_irq_remapping.c | 18 +++++++++++++-----
    1 file changed, 13 insertions(+), 5 deletions(-)

    diff --git a/drivers/iommu/intel_irq_remapping.c b/drivers/iommu/intel_irq_remapping.c
    index e0b18f3..af8904d 100644
    --- a/drivers/iommu/intel_irq_remapping.c
    +++ b/drivers/iommu/intel_irq_remapping.c
    @@ -736,6 +736,7 @@ int __init parse_ioapics_under_ir(void)
    {
    struct dmar_drhd_unit *drhd;
    int ir_supported = 0;
    + int ioapic_idx;

    for_each_drhd_unit(drhd) {
    struct intel_iommu *iommu = drhd->iommu;
    @@ -748,13 +749,20 @@ int __init parse_ioapics_under_ir(void)
    }
    }

    - if (ir_supported && ir_ioapic_num != nr_ioapics) {
    - printk(KERN_WARNING
    - "Not all IO-APIC's listed under remapping hardware\n");
    - return -1;
    + if (!ir_supported)
    + return 0;
    +
    + for (ioapic_idx = 0; ioapic_idx < nr_ioapics; ioapic_idx++) {
    + int ioapic_id = mpc_ioapic_id(ioapic_idx);
    + if (!map_ioapic_to_ir(ioapic_id)) {
    + pr_err(FW_BUG "ioapic %d has no mapping iommu, "
    + "interrupt remapping will be disabled\n",
    + ioapic_id);
    + return -1;
    + }
    }

    - return ir_supported;
    + return 1;
    }

    int __init ir_dev_scope_init(void)
    --
    1.7.9.5


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