Linux kernel IOMMU代码分析笔记（8）——intel_enable_irq_remapping（2）

接上文。

（4）

for_each_iommu(iommu, drhd) {
    /*
     * If the queued invalidation is already initialized,
     * shouldn't disable it.
     */
    if (iommu->qi)
        continue;

    /*
     * Clear previous faults.
     */
    dmar_fault(-1, iommu);

    /*
     * Disable intr remapping and queued invalidation, if already
     * enabled prior to OS handover.
     */
    iommu_disable_irq_remapping(iommu);

    dmar_disable_qi(iommu);
}

上面代码含义是如果硬件单元的queued invalidation还没有初始化，则清掉之前的fault，并且disable IRQ remapping和queued invalidation。

（5）

/*
 * check for the Interrupt-remapping support
 */
for_each_iommu(iommu, drhd) {
    if (!ecap_ir_support(iommu->ecap))
        continue;

    if (eim && !ecap_eim_support(iommu->ecap)) {
        printk(KERN_INFO "DRHD %Lx: EIM not supported by DRHD, "
               " ecap %Lx\n", drhd->reg_base_addr, iommu->ecap);
        goto error;
    }
}

上述代码含义是如果硬件支持IRQ remapping并且系统支持x2APIC模式，如果硬件不支持x2APIC模式，就失败。

（6）

/*
 * Enable queued invalidation for all the DRHD's.
 */
for_each_iommu(iommu, drhd) {
    int ret = dmar_enable_qi(iommu);

    if (ret) {
        printk(KERN_ERR "DRHD %Lx: failed to enable queued, "
               " invalidation, ecap %Lx, ret %d\n",
               drhd->reg_base_addr, iommu->ecap, ret);
        goto error;
    }
}

/*
 * Setup Interrupt-remapping for all the DRHD's now.
 */
for_each_iommu(iommu, drhd) {
    if (!ecap_ir_support(iommu->ecap))
        continue;

    if (intel_setup_irq_remapping(iommu, eim))
        goto error;

    setup = 1;
}

if (!setup)
    goto error;

上述代码分别为每个硬件单元enable queued invalidation和IRQ remapping。

（7）

irq_remapping_enabled = 1;

/*
 * VT-d has a different layout for IO-APIC entries when
 * interrupt remapping is enabled. So it needs a special routine
 * to print IO-APIC entries for debugging purposes too.
 */
x86_io_apic_ops.print_entries = intel_ir_io_apic_print_entries;

pr_info("Enabled IRQ remapping in %s mode\n", eim ? "x2apic" : "xapic");

return eim ? IRQ_REMAP_X2APIC_MODE : IRQ_REMAP_XAPIC_MODE;

error:
    /*
     * handle error condition gracefully here!
     */

if (x2apic_present)
    pr_warn("Failed to enable irq remapping.  You are vulnerable to irq-injection attacks.\n");

return -1;

如果成功的话，返回IRQ_REMAP_XAPIC_MODE（0）或IRQ_REMAP_X2APIC_MODE（1），否则返回-1。

参考资料：
"BIOS Considerations" in *Intel ® Virtualization Technology for Directed I/O