These patches reset PCIe devices at boot time to address DMA problem on kdump with iommu. When "reset_devices" is specified, a hot reset is triggered on each PCIe root port and downstream port to reset its downstream endpoint. Background: A kdump problem about DMA has been discussed for a long time. That is, when a kernel is switched to the kdump kernel DMA derived from first kernel affects second kernel. Recently this problem surfaces when iommu is used for PCI passthrough on KVM guest. In the case of the machine I use, when intel_iommu=on is specified, DMAR error is detected in kdump kernel and PCI SERR is also detected. Finally kdump fails because some devices does not work correctly. The root cause is that ongoing DMA from first kernel causes DMAR fault because page table of DMAR is initialized while kdump kernel is booting up. Therefore to address this problem DMA needs to be stopped before DMAR is initialized at kdump kernel boot time. By these patches, PCIe devices are reset by hot reset and its DMA is stopped when reset_devices is specified. One problem of this solution is that the monitor blacks out when VGA controller is reset. So this patch does not reset the port whose child endpoint is VGA device. v2: Reset devices in setup_arch() because reset need to be done before interrupt remapping is initialized. v1: https://lkml.org/lkml/2012/8/3/160 Thanks, Takao Indoh -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
