On Wed, Jan 04, 2023 at 10:52:55AM +0100, Niklas Schnelle wrote: > The problem manifests only with ISM devices which are a special s390 > virtual PCI device that is implemented in the machine hypervisor. This > device is used for high speed cross-LPAR (Logical Partition) > communication, basically it allows two LPARs that previously exchanged > an authentication token to memcpy between their partitioned memory > using the virtual device. For copying a receiving LPAR will IOMMU map a > region of memory for the ISM device that it will allow DMAing into > (memcpy by the hypervisor). All other regions remain unmapped and thus > inaccessible. In preparation the device emulation in the machine > hypervisor intercepts the IOTLB flush and looks at the IOMMU > translation tables performing e.g. size and alignment checks I presume, > one of these checks against the start/end DMA boundaries. This check > fails which leads to the virtual ISM device being put into an error > state. Being in an error state it then fails to be initialized by the > guest driver later on. You could rephrase this as saying that the S390 map operation doesn't check for bounds so mapping in a reserved region doesn't fail, but errors the HW. Which seems reasonable to me Jason
