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diff --git a/Documentation/virt/kvm/devices/xive.rst b/Documentation/virt/kvm/devices/xive.rst new file mode 100644 index 000000000..8bdf3dc38 --- /dev/null +++ b/Documentation/virt/kvm/devices/xive.rst @@ -0,0 +1,247 @@ +.. SPDX-License-Identifier: GPL-2.0 + +=========================================================== +POWER9 eXternal Interrupt Virtualization Engine (XIVE Gen1) +=========================================================== + +Device types supported: + - KVM_DEV_TYPE_XIVE POWER9 XIVE Interrupt Controller generation 1 + +This device acts as a VM interrupt controller. It provides the KVM +interface to configure the interrupt sources of a VM in the underlying +POWER9 XIVE interrupt controller. + +Only one XIVE instance may be instantiated. A guest XIVE device +requires a POWER9 host and the guest OS should have support for the +XIVE native exploitation interrupt mode. If not, it should run using +the legacy interrupt mode, referred as XICS (POWER7/8). + +* Device Mappings + + The KVM device exposes different MMIO ranges of the XIVE HW which + are required for interrupt management. These are exposed to the + guest in VMAs populated with a custom VM fault handler. + + 1. Thread Interrupt Management Area (TIMA) + + Each thread has an associated Thread Interrupt Management context + composed of a set of registers. These registers let the thread + handle priority management and interrupt acknowledgment. The most + important are : + + - Interrupt Pending Buffer (IPB) + - Current Processor Priority (CPPR) + - Notification Source Register (NSR) + + They are exposed to software in four different pages each proposing + a view with a different privilege. The first page is for the + physical thread context and the second for the hypervisor. Only the + third (operating system) and the fourth (user level) are exposed the + guest. + + 2. Event State Buffer (ESB) + + Each source is associated with an Event State Buffer (ESB) with + either a pair of even/odd pair of pages which provides commands to + manage the source: to trigger, to EOI, to turn off the source for + instance. + + 3. Device pass-through + + When a device is passed-through into the guest, the source + interrupts are from a different HW controller (PHB4) and the ESB + pages exposed to the guest should accommadate this change. + + The passthru_irq helpers, kvmppc_xive_set_mapped() and + kvmppc_xive_clr_mapped() are called when the device HW irqs are + mapped into or unmapped from the guest IRQ number space. The KVM + device extends these helpers to clear the ESB pages of the guest IRQ + number being mapped and then lets the VM fault handler repopulate. + The handler will insert the ESB page corresponding to the HW + interrupt of the device being passed-through or the initial IPI ESB + page if the device has being removed. + + The ESB remapping is fully transparent to the guest and the OS + device driver. All handling is done within VFIO and the above + helpers in KVM-PPC. + +* Groups: + +1. KVM_DEV_XIVE_GRP_CTRL + Provides global controls on the device + + Attributes: + 1.1 KVM_DEV_XIVE_RESET (write only) + Resets the interrupt controller configuration for sources and event + queues. To be used by kexec and kdump. + + Errors: none + + 1.2 KVM_DEV_XIVE_EQ_SYNC (write only) + Sync all the sources and queues and mark the EQ pages dirty. This + to make sure that a consistent memory state is captured when + migrating the VM. + + Errors: none + + 1.3 KVM_DEV_XIVE_NR_SERVERS (write only) + The kvm_device_attr.addr points to a __u32 value which is the number of + interrupt server numbers (ie, highest possible vcpu id plus one). + + Errors: + + ======= ========================================== + -EINVAL Value greater than KVM_MAX_VCPU_ID. + -EFAULT Invalid user pointer for attr->addr. + -EBUSY A vCPU is already connected to the device. + ======= ========================================== + +2. KVM_DEV_XIVE_GRP_SOURCE (write only) + Initializes a new source in the XIVE device and mask it. + + Attributes: + Interrupt source number (64-bit) + + The kvm_device_attr.addr points to a __u64 value:: + + bits: | 63 .... 2 | 1 | 0 + values: | unused | level | type + + - type: 0:MSI 1:LSI + - level: assertion level in case of an LSI. + + Errors: + + ======= ========================================== + -E2BIG Interrupt source number is out of range + -ENOMEM Could not create a new source block + -EFAULT Invalid user pointer for attr->addr. + -ENXIO Could not allocate underlying HW interrupt + ======= ========================================== + +3. KVM_DEV_XIVE_GRP_SOURCE_CONFIG (write only) + Configures source targeting + + Attributes: + Interrupt source number (64-bit) + + The kvm_device_attr.addr points to a __u64 value:: + + bits: | 63 .... 33 | 32 | 31 .. 3 | 2 .. 0 + values: | eisn | mask | server | priority + + - priority: 0-7 interrupt priority level + - server: CPU number chosen to handle the interrupt + - mask: mask flag (unused) + - eisn: Effective Interrupt Source Number + + Errors: + + ======= ======================================================= + -ENOENT Unknown source number + -EINVAL Not initialized source number + -EINVAL Invalid priority + -EINVAL Invalid CPU number. + -EFAULT Invalid user pointer for attr->addr. + -ENXIO CPU event queues not configured or configuration of the + underlying HW interrupt failed + -EBUSY No CPU available to serve interrupt + ======= ======================================================= + +4. KVM_DEV_XIVE_GRP_EQ_CONFIG (read-write) + Configures an event queue of a CPU + + Attributes: + EQ descriptor identifier (64-bit) + + The EQ descriptor identifier is a tuple (server, priority):: + + bits: | 63 .... 32 | 31 .. 3 | 2 .. 0 + values: | unused | server | priority + + The kvm_device_attr.addr points to:: + + struct kvm_ppc_xive_eq { + __u32 flags; + __u32 qshift; + __u64 qaddr; + __u32 qtoggle; + __u32 qindex; + __u8 pad[40]; + }; + + - flags: queue flags + KVM_XIVE_EQ_ALWAYS_NOTIFY (required) + forces notification without using the coalescing mechanism + provided by the XIVE END ESBs. + - qshift: queue size (power of 2) + - qaddr: real address of queue + - qtoggle: current queue toggle bit + - qindex: current queue index + - pad: reserved for future use + + Errors: + + ======= ========================================= + -ENOENT Invalid CPU number + -EINVAL Invalid priority + -EINVAL Invalid flags + -EINVAL Invalid queue size + -EINVAL Invalid queue address + -EFAULT Invalid user pointer for attr->addr. + -EIO Configuration of the underlying HW failed + ======= ========================================= + +5. KVM_DEV_XIVE_GRP_SOURCE_SYNC (write only) + Synchronize the source to flush event notifications + + Attributes: + Interrupt source number (64-bit) + + Errors: + + ======= ============================= + -ENOENT Unknown source number + -EINVAL Not initialized source number + ======= ============================= + +* VCPU state + + The XIVE IC maintains VP interrupt state in an internal structure + called the NVT. When a VP is not dispatched on a HW processor + thread, this structure can be updated by HW if the VP is the target + of an event notification. + + It is important for migration to capture the cached IPB from the NVT + as it synthesizes the priorities of the pending interrupts. We + capture a bit more to report debug information. + + KVM_REG_PPC_VP_STATE (2 * 64bits):: + + bits: | 63 .... 32 | 31 .... 0 | + values: | TIMA word0 | TIMA word1 | + bits: | 127 .......... 64 | + values: | unused | + +* Migration: + + Saving the state of a VM using the XIVE native exploitation mode + should follow a specific sequence. When the VM is stopped : + + 1. Mask all sources (PQ=01) to stop the flow of events. + + 2. Sync the XIVE device with the KVM control KVM_DEV_XIVE_EQ_SYNC to + flush any in-flight event notification and to stabilize the EQs. At + this stage, the EQ pages are marked dirty to make sure they are + transferred in the migration sequence. + + 3. Capture the state of the source targeting, the EQs configuration + and the state of thread interrupt context registers. + + Restore is similar: + + 1. Restore the EQ configuration. As targeting depends on it. + 2. Restore targeting + 3. Restore the thread interrupt contexts + 4. Restore the source states + 5. Let the vCPU run |