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Diffstat (limited to 'Documentation/admin-guide/kernel-parameters.txt')
| -rw-r--r-- | Documentation/admin-guide/kernel-parameters.txt | 49 |
1 files changed, 49 insertions, 0 deletions
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index aa0031108bc1..8d62a6fdb152 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3079,6 +3079,26 @@ Kernel parameters Default is Y (on). + kvm.enable_pmu=[KVM,X86] + If enabled, KVM will virtualize PMU functionality based + on the virtual CPU model defined by userspace. This + can be overridden on a per-VM basis via + KVM_CAP_PMU_CAPABILITY. + + If disabled, KVM will not virtualize PMU functionality, + e.g. MSRs, PMCs, PMIs, etc., even if userspace defines + a virtual CPU model that contains PMU assets. + + Note, KVM's vPMU support implicitly requires running + with an in-kernel local APIC, e.g. to deliver PMIs to + the guest. Running without an in-kernel local APIC is + not supported, though KVM will allow such a combination + (with severely degraded functionality). + + See also enable_mediated_pmu. + + Default is Y (on). + kvm.enable_virt_at_load=[KVM,ARM64,LOONGARCH,MIPS,RISCV,X86] If enabled, KVM will enable virtualization in hardware when KVM is loaded, and disable virtualization when KVM @@ -3125,6 +3145,35 @@ Kernel parameters If the value is 0 (the default), KVM will pick a period based on the ratio, such that a page is zapped after 1 hour on average. + kvm-{amd,intel}.enable_mediated_pmu=[KVM,AMD,INTEL] + If enabled, KVM will provide a mediated virtual PMU, + instead of the default perf-based virtual PMU (if + kvm.enable_pmu is true and PMU is enumerated via the + virtual CPU model). + + With a perf-based vPMU, KVM operates as a user of perf, + i.e. emulates guest PMU counters using perf events. + KVM-created perf events are managed by perf as regular + (guest-only) events, e.g. are scheduled in/out, contend + for hardware resources, etc. Using a perf-based vPMU + allows guest and host usage of the PMU to co-exist, but + incurs non-trivial overhead and can result in silently + dropped guest events (due to resource contention). + + With a mediated vPMU, hardware PMU state is context + switched around the world switch to/from the guest. + KVM mediates which events the guest can utilize, but + gives the guest direct access to all other PMU assets + when possible (KVM may intercept some accesses if the + virtual CPU model provides a subset of hardware PMU + functionality). Using a mediated vPMU significantly + reduces PMU virtualization overhead and eliminates lost + guest events, but is mutually exclusive with using perf + to profile KVM guests and adds latency to most VM-Exits + (to context switch PMU state). + + Default is N (off). + kvm-amd.nested= [KVM,AMD] Control nested virtualization feature in KVM/SVM. Default is 1 (enabled). |