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247 lines
8.2 KiB
247 lines
8.2 KiB
.. SPDX-License-Identifier: GPL-2.0 |
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=========================================================== |
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POWER9 eXternal Interrupt Virtualization Engine (XIVE Gen1) |
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=========================================================== |
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Device types supported: |
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- KVM_DEV_TYPE_XIVE POWER9 XIVE Interrupt Controller generation 1 |
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This device acts as a VM interrupt controller. It provides the KVM |
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interface to configure the interrupt sources of a VM in the underlying |
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POWER9 XIVE interrupt controller. |
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Only one XIVE instance may be instantiated. A guest XIVE device |
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requires a POWER9 host and the guest OS should have support for the |
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XIVE native exploitation interrupt mode. If not, it should run using |
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the legacy interrupt mode, referred as XICS (POWER7/8). |
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* Device Mappings |
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The KVM device exposes different MMIO ranges of the XIVE HW which |
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are required for interrupt management. These are exposed to the |
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guest in VMAs populated with a custom VM fault handler. |
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1. Thread Interrupt Management Area (TIMA) |
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Each thread has an associated Thread Interrupt Management context |
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composed of a set of registers. These registers let the thread |
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handle priority management and interrupt acknowledgment. The most |
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important are : |
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- Interrupt Pending Buffer (IPB) |
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- Current Processor Priority (CPPR) |
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- Notification Source Register (NSR) |
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They are exposed to software in four different pages each proposing |
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a view with a different privilege. The first page is for the |
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physical thread context and the second for the hypervisor. Only the |
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third (operating system) and the fourth (user level) are exposed the |
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guest. |
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2. Event State Buffer (ESB) |
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Each source is associated with an Event State Buffer (ESB) with |
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either a pair of even/odd pair of pages which provides commands to |
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manage the source: to trigger, to EOI, to turn off the source for |
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instance. |
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3. Device pass-through |
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When a device is passed-through into the guest, the source |
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interrupts are from a different HW controller (PHB4) and the ESB |
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pages exposed to the guest should accommadate this change. |
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The passthru_irq helpers, kvmppc_xive_set_mapped() and |
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kvmppc_xive_clr_mapped() are called when the device HW irqs are |
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mapped into or unmapped from the guest IRQ number space. The KVM |
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device extends these helpers to clear the ESB pages of the guest IRQ |
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number being mapped and then lets the VM fault handler repopulate. |
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The handler will insert the ESB page corresponding to the HW |
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interrupt of the device being passed-through or the initial IPI ESB |
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page if the device has being removed. |
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The ESB remapping is fully transparent to the guest and the OS |
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device driver. All handling is done within VFIO and the above |
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helpers in KVM-PPC. |
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* Groups: |
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1. KVM_DEV_XIVE_GRP_CTRL |
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Provides global controls on the device |
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Attributes: |
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1.1 KVM_DEV_XIVE_RESET (write only) |
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Resets the interrupt controller configuration for sources and event |
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queues. To be used by kexec and kdump. |
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Errors: none |
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1.2 KVM_DEV_XIVE_EQ_SYNC (write only) |
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Sync all the sources and queues and mark the EQ pages dirty. This |
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to make sure that a consistent memory state is captured when |
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migrating the VM. |
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Errors: none |
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1.3 KVM_DEV_XIVE_NR_SERVERS (write only) |
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The kvm_device_attr.addr points to a __u32 value which is the number of |
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interrupt server numbers (ie, highest possible vcpu id plus one). |
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Errors: |
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======= ========================================== |
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-EINVAL Value greater than KVM_MAX_VCPU_IDS. |
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-EFAULT Invalid user pointer for attr->addr. |
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-EBUSY A vCPU is already connected to the device. |
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======= ========================================== |
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2. KVM_DEV_XIVE_GRP_SOURCE (write only) |
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Initializes a new source in the XIVE device and mask it. |
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Attributes: |
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Interrupt source number (64-bit) |
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The kvm_device_attr.addr points to a __u64 value:: |
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bits: | 63 .... 2 | 1 | 0 |
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values: | unused | level | type |
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- type: 0:MSI 1:LSI |
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- level: assertion level in case of an LSI. |
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Errors: |
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======= ========================================== |
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-E2BIG Interrupt source number is out of range |
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-ENOMEM Could not create a new source block |
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-EFAULT Invalid user pointer for attr->addr. |
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-ENXIO Could not allocate underlying HW interrupt |
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======= ========================================== |
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3. KVM_DEV_XIVE_GRP_SOURCE_CONFIG (write only) |
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Configures source targeting |
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Attributes: |
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Interrupt source number (64-bit) |
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The kvm_device_attr.addr points to a __u64 value:: |
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bits: | 63 .... 33 | 32 | 31 .. 3 | 2 .. 0 |
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values: | eisn | mask | server | priority |
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- priority: 0-7 interrupt priority level |
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- server: CPU number chosen to handle the interrupt |
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- mask: mask flag (unused) |
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- eisn: Effective Interrupt Source Number |
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Errors: |
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======= ======================================================= |
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-ENOENT Unknown source number |
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-EINVAL Not initialized source number |
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-EINVAL Invalid priority |
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-EINVAL Invalid CPU number. |
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-EFAULT Invalid user pointer for attr->addr. |
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-ENXIO CPU event queues not configured or configuration of the |
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underlying HW interrupt failed |
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-EBUSY No CPU available to serve interrupt |
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======= ======================================================= |
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4. KVM_DEV_XIVE_GRP_EQ_CONFIG (read-write) |
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Configures an event queue of a CPU |
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Attributes: |
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EQ descriptor identifier (64-bit) |
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The EQ descriptor identifier is a tuple (server, priority):: |
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bits: | 63 .... 32 | 31 .. 3 | 2 .. 0 |
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values: | unused | server | priority |
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The kvm_device_attr.addr points to:: |
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struct kvm_ppc_xive_eq { |
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__u32 flags; |
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__u32 qshift; |
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__u64 qaddr; |
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__u32 qtoggle; |
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__u32 qindex; |
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__u8 pad[40]; |
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}; |
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- flags: queue flags |
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KVM_XIVE_EQ_ALWAYS_NOTIFY (required) |
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forces notification without using the coalescing mechanism |
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provided by the XIVE END ESBs. |
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- qshift: queue size (power of 2) |
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- qaddr: real address of queue |
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- qtoggle: current queue toggle bit |
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- qindex: current queue index |
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- pad: reserved for future use |
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Errors: |
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======= ========================================= |
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-ENOENT Invalid CPU number |
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-EINVAL Invalid priority |
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-EINVAL Invalid flags |
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-EINVAL Invalid queue size |
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-EINVAL Invalid queue address |
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-EFAULT Invalid user pointer for attr->addr. |
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-EIO Configuration of the underlying HW failed |
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======= ========================================= |
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5. KVM_DEV_XIVE_GRP_SOURCE_SYNC (write only) |
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Synchronize the source to flush event notifications |
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Attributes: |
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Interrupt source number (64-bit) |
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Errors: |
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======= ============================= |
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-ENOENT Unknown source number |
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-EINVAL Not initialized source number |
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======= ============================= |
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* VCPU state |
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The XIVE IC maintains VP interrupt state in an internal structure |
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called the NVT. When a VP is not dispatched on a HW processor |
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thread, this structure can be updated by HW if the VP is the target |
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of an event notification. |
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It is important for migration to capture the cached IPB from the NVT |
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as it synthesizes the priorities of the pending interrupts. We |
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capture a bit more to report debug information. |
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KVM_REG_PPC_VP_STATE (2 * 64bits):: |
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bits: | 63 .... 32 | 31 .... 0 | |
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values: | TIMA word0 | TIMA word1 | |
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bits: | 127 .......... 64 | |
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values: | unused | |
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* Migration: |
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Saving the state of a VM using the XIVE native exploitation mode |
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should follow a specific sequence. When the VM is stopped : |
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1. Mask all sources (PQ=01) to stop the flow of events. |
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2. Sync the XIVE device with the KVM control KVM_DEV_XIVE_EQ_SYNC to |
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flush any in-flight event notification and to stabilize the EQs. At |
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this stage, the EQ pages are marked dirty to make sure they are |
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transferred in the migration sequence. |
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3. Capture the state of the source targeting, the EQs configuration |
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and the state of thread interrupt context registers. |
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Restore is similar: |
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1. Restore the EQ configuration. As targeting depends on it. |
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2. Restore targeting |
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3. Restore the thread interrupt contexts |
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4. Restore the source states |
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5. Let the vCPU run
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