| ================================ |
| POWER9 XIVE interrupt controller |
| ================================ |
| |
| The POWER9 processor comes with a new interrupt controller |
| architecture, called XIVE as "eXternal Interrupt Virtualization |
| Engine". |
| |
| Compared to the previous architecture, the main characteristics of |
| XIVE are to support a larger number of interrupt sources and to |
| deliver interrupts directly to virtual processors without hypervisor |
| assistance. This removes the context switches required for the |
| delivery process. |
| |
| |
| XIVE architecture |
| ================= |
| |
| The XIVE IC is composed of three sub-engines, each taking care of a |
| processing layer of external interrupts: |
| |
| - Interrupt Virtualization Source Engine (IVSE), or Source Controller |
| (SC). These are found in PCI PHBs, in the Processor Service |
| Interface (PSI) host bridge Controller, but also inside the main |
| controller for the core IPIs and other sub-chips (NX, CAP, NPU) of |
| the chip/processor. They are configured to feed the IVRE with |
| events. |
| - Interrupt Virtualization Routing Engine (IVRE) or Virtualization |
| Controller (VC). It handles event coalescing and perform interrupt |
| routing by matching an event source number with an Event |
| Notification Descriptor (END). |
| - Interrupt Virtualization Presentation Engine (IVPE) or Presentation |
| Controller (PC). It maintains the interrupt context state of each |
| thread and handles the delivery of the external interrupt to the |
| thread. |
| |
| :: |
| |
| XIVE Interrupt Controller |
| +------------------------------------+ IPIs |
| | +---------+ +---------+ +--------+ | +-------+ |
| | |IVRE | |Common Q | |IVPE |----> | CORES | |
| | | esb | | | | |----> | | |
| | | eas | | Bridge | | tctx |----> | | |
| | |SC end | | | | nvt | | | | |
| +------+ | +---------+ +----+----+ +--------+ | +-+-+-+-+ |
| | RAM | +------------------|-----------------+ | | | |
| | | | | | | |
| | | | | | | |
| | | +--------------------v------------------------v-v-v--+ other |
| | <--+ Power Bus +--> chips |
| | esb | +---------+-----------------------+------------------+ |
| | eas | | | |
| | end | +--|------+ | |
| | nvt | +----+----+ | +----+----+ |
| +------+ |IVSE | | |IVSE | |
| | | | | | |
| | PQ-bits | | | PQ-bits | |
| | local |-+ | in VC | |
| +---------+ +---------+ |
| PCIe NX,NPU,CAPI |
| |
| |
| PQ-bits: 2 bits source state machine (P:pending Q:queued) |
| esb: Event State Buffer (Array of PQ bits in an IVSE) |
| eas: Event Assignment Structure |
| end: Event Notification Descriptor |
| nvt: Notification Virtual Target |
| tctx: Thread interrupt Context registers |
| |
| |
| |
| XIVE internal tables |
| -------------------- |
| |
| Each of the sub-engines uses a set of tables to redirect interrupts |
| from event sources to CPU threads. |
| |
| :: |
| |
| +-------+ |
| User or O/S | EQ | |
| or +------>|entries| |
| Hypervisor | | .. | |
| Memory | +-------+ |
| | ^ |
| | | |
| +-------------------------------------------------+ |
| | | |
| Hypervisor +------+ +---+--+ +---+--+ +------+ |
| Memory | ESB | | EAT | | ENDT | | NVTT | |
| (skiboot) +----+-+ +----+-+ +----+-+ +------+ |
| ^ | ^ | ^ | ^ |
| | | | | | | | |
| +-------------------------------------------------+ |
| | | | | | | | |
| | | | | | | | |
| +----|--|--------|--|--------|--|-+ +-|-----+ +------+ |
| | | | | | | | | | | tctx| |Thread| |
| IPI or ---+ + v + v + v |---| + .. |-----> | |
| HW events | | | | | | |
| | IVRE | | IVPE | +------+ |
| +---------------------------------+ +-------+ |
| |
| |
| The IVSE have a 2-bits state machine, P for pending and Q for queued, |
| for each source that allows events to be triggered. They are stored in |
| an Event State Buffer (ESB) array and can be controlled by MMIOs. |
| |
| If the event is let through, the IVRE looks up in the Event Assignment |
| Structure (EAS) table for an Event Notification Descriptor (END) |
| configured for the source. Each Event Notification Descriptor defines |
| a notification path to a CPU and an in-memory Event Queue, in which |
| will be enqueued an EQ data for the O/S to pull. |
| |
| The IVPE determines if a Notification Virtual Target (NVT) can handle |
| the event by scanning the thread contexts of the VCPUs dispatched on |
| the processor HW threads. It maintains the interrupt context state of |
| each thread in a NVT table. |
| |
| XIVE thread interrupt context |
| ----------------------------- |
| |
| The XIVE presenter can generate four different exceptions to its |
| HW threads: |
| |
| - hypervisor exception |
| - O/S exception |
| - Event-Based Branch (user level) |
| - msgsnd (doorbell) |
| |
| Each exception has a state independent from the others called a Thread |
| Interrupt Management context. This context is a set of registers which |
| lets the thread handle priority management and interrupt |
| acknowledgment among other things. The most important ones being : |
| |
| - Interrupt Priority Register (PIPR) |
| - Interrupt Pending Buffer (IPB) |
| - Current Processor Priority (CPPR) |
| - Notification Source Register (NSR) |
| |
| TIMA |
| ~~~~ |
| |
| The Thread Interrupt Management registers are accessible through a |
| specific MMIO region, called the Thread Interrupt Management Area |
| (TIMA), four aligned pages, each exposing a different view of the |
| registers. First page (page address ending in ``0b00``) gives access |
| to the entire context and is reserved for the ring 0 view for the |
| physical thread context. The second (page address ending in ``0b01``) |
| is for the hypervisor, ring 1 view. The third (page address ending in |
| ``0b10``) is for the operating system, ring 2 view. The fourth (page |
| address ending in ``0b11``) is for user level, ring 3 view. |
| |
| Interrupt flow from an O/S perspective |
| ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
| |
| After an event data has been enqueued in the O/S Event Queue, the IVPE |
| raises the bit corresponding to the priority of the pending interrupt |
| in the register IBP (Interrupt Pending Buffer) to indicate that an |
| event is pending in one of the 8 priority queues. The Pending |
| Interrupt Priority Register (PIPR) is also updated using the IPB. This |
| register represent the priority of the most favored pending |
| notification. |
| |
| The PIPR is then compared to the the Current Processor Priority |
| Register (CPPR). If it is more favored (numerically less than), the |
| CPU interrupt line is raised and the EO bit of the Notification Source |
| Register (NSR) is updated to notify the presence of an exception for |
| the O/S. The O/S acknowledges the interrupt with a special load in the |
| Thread Interrupt Management Area. |
| |
| The O/S handles the interrupt and when done, performs an EOI using a |
| MMIO operation on the ESB management page of the associate source. |
| |
| Overview of the QEMU models for XIVE |
| ==================================== |
| |
| The XiveSource models the IVSE in general, internal and external. It |
| handles the source ESBs and the MMIO interface to control them. |
| |
| The XiveNotifier is a small helper interface interconnecting the |
| XiveSource to the XiveRouter. |
| |
| The XiveRouter is an abstract model acting as a combined IVRE and |
| IVPE. It routes event notifications using the EAS and END tables to |
| the IVPE sub-engine which does a CAM scan to find a CPU to deliver the |
| exception. Storage should be provided by the inheriting classes. |
| |
| XiveEnDSource is a special source object. It exposes the END ESB MMIOs |
| of the Event Queues which are used for coalescing event notifications |
| and for escalation. Not used on the field, only to sync the EQ cache |
| in OPAL. |
| |
| Finally, the XiveTCTX contains the interrupt state context of a thread, |
| four sets of registers, one for each exception that can be delivered |
| to a CPU. These contexts are scanned by the IVPE to find a matching VP |
| when a notification is triggered. It also models the Thread Interrupt |
| Management Area (TIMA), which exposes the thread context registers to |
| the CPU for interrupt management. |
