From: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> KVM_HC_KICK_CPU hypercall added to wakeup halted vcpu in paravirtual spinlock enabled guest. KVM_FEATURE_PV_UNHALT enables guest to check whether pv spinlock can be enabled in guest. support in host is queried via ioctl(KVM_CHECK_EXTENSION, KVM_CAP_PV_UNHALT) Thanks Alex for KVM_HC_FEATURES inputs and Vatsa for rewriting KVM_HC_KICK_CPU Signed-off-by: Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx> Signed-off-by: Raghavendra K T <raghavendra.kt@xxxxxxxxxxxxxxxxxx> --- diff --git a/Documentation/virtual/kvm/api.txt b/Documentation/virtual/kvm/api.txt index 6386f8c..7e2eba0 100644 --- a/Documentation/virtual/kvm/api.txt +++ b/Documentation/virtual/kvm/api.txt @@ -1119,6 +1119,13 @@ support. Instead it is reported via if that returns true and you use KVM_CREATE_IRQCHIP, or if you emulate the feature in userspace, then you can enable the feature for KVM_SET_CPUID2. +Paravirtualized ticket spinlocks can be enabled in guest by checking whether +support exists in host via, + + ioctl(KVM_CHECK_EXTENSION, KVM_CAP_PV_UNHALT) + +if this call return true, guest can use the feature. + 4.47 KVM_PPC_GET_PVINFO Capability: KVM_CAP_PPC_GET_PVINFO diff --git a/Documentation/virtual/kvm/cpuid.txt b/Documentation/virtual/kvm/cpuid.txt index 8820685..062dff9 100644 --- a/Documentation/virtual/kvm/cpuid.txt +++ b/Documentation/virtual/kvm/cpuid.txt @@ -39,6 +39,10 @@ KVM_FEATURE_CLOCKSOURCE2 || 3 || kvmclock available at msrs KVM_FEATURE_ASYNC_PF || 4 || async pf can be enabled by || || writing to msr 0x4b564d02 ------------------------------------------------------------------------------ +KVM_FEATURE_PV_UNHALT || 6 || guest checks this feature bit + || || before enabling paravirtualized + || || spinlock support. +------------------------------------------------------------------------------ KVM_FEATURE_CLOCKSOURCE_STABLE_BIT || 24 || host will warn if no guest-side || || per-cpu warps are expected in || || kvmclock. diff --git a/Documentation/virtual/kvm/hypercalls.txt b/Documentation/virtual/kvm/hypercalls.txt new file mode 100644 index 0000000..c9e8b9c --- /dev/null +++ b/Documentation/virtual/kvm/hypercalls.txt @@ -0,0 +1,59 @@ +KVM Hypercalls Documentation +=========================== +Template for documentation is +The documenenation for hypercalls should inlcude +1. Hypercall name, value. +2. Architecture(s) +3. status (deprecated, obsolete, active) +4. Purpose + + +1. KVM_HC_VAPIC_POLL_IRQ +------------------------ +value: 1 +Architecture: x86 +Purpose: + +2. KVM_HC_MMU_OP +------------------------ +value: 2 +Architecture: x86 +status: deprecated. +Purpose: Support MMU operations such as writing to PTE, +flushing TLB, release PT. + +3. KVM_HC_FEATURES +------------------------ +value: 3 +Architecture: PPC +Purpose: Expose hypercall availability to the guest. On x86 platforms, cpuid +used to enumerate which hypercalls are available. On PPC, either device tree +based lookup ( which is also what EPAPR dictates) OR KVM specific enumeration +mechanism (which is this hypercall) can be used. + +4. KVM_HC_PPC_MAP_MAGIC_PAGE +------------------------ +value: 4 +Architecture: PPC +Purpose: To enable communication between the hypervisor and guest there is a +shared page that contains parts of supervisor visible register state. +The guest can map this shared page to access its supervisor register through +memory using this hypercall. + +5. KVM_HC_KICK_CPU +------------------------ +value: 5 +Architecture: x86 +Purpose: Hypercall used to wakeup a vcpu from HLT state + +Usage example : A vcpu of a paravirtualized guest that is busywaiting in guest +kernel mode for an event to occur (ex: a spinlock to become available) can +execute HLT instruction once it has busy-waited for more than a threshold +time-interval. Execution of HLT instruction would cause the hypervisor to put +the vcpu to sleep until occurence of an appropriate event. Another vcpu of the +same guest can wakeup the sleeping vcpu by issuing KVM_HC_KICK_CPU hypercall, +specifying APIC ID of the vcpu to be wokenup. + +TODO: +1. more information on input and output needed? +2. Add more detail to purpose of hypercalls. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html