From c32b1b896d2ab30ac30bc39194bac47a09f7f497 Mon Sep 17 00:00:00 2001 From: Chenyi Qiang Date: Fri, 6 Nov 2020 17:03:15 +0800 Subject: [PATCH] KVM: X86: Add the Document for KVM_CAP_X86_BUS_LOCK_EXIT Introduce a new capability named KVM_CAP_X86_BUS_LOCK_EXIT, which is used to handle bus locks detected in guest. It allows the userspace to do custom throttling policies to mitigate the 'noisy neighbour' problem. Signed-off-by: Chenyi Qiang Message-Id: <20201106090315.18606-5-chenyi.qiang@intel.com> Signed-off-by: Paolo Bonzini --- Documentation/virt/kvm/api.rst | 45 +++++++++++++++++++++++++++++++++++++++--- 1 file changed, 42 insertions(+), 3 deletions(-) diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index 99ceb978c8b0..effcc08733fd 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -4893,9 +4893,11 @@ local APIC is not used. __u16 flags; More architecture-specific flags detailing state of the VCPU that may -affect the device's behavior. The only currently defined flag is -KVM_RUN_X86_SMM, which is valid on x86 machines and is set if the -VCPU is in system management mode. +affect the device's behavior. Current defined flags: + /* x86, set if the VCPU is in system management mode */ + #define KVM_RUN_X86_SMM (1 << 0) + /* x86, set if bus lock detected in VM */ + #define KVM_RUN_BUS_LOCK (1 << 1) :: @@ -6038,6 +6040,43 @@ KVM_EXIT_X86_RDMSR and KVM_EXIT_X86_WRMSR exit notifications which user space can then handle to implement model specific MSR handling and/or user notifications to inform a user that an MSR was not handled. +7.22 KVM_CAP_X86_BUS_LOCK_EXIT +------------------------------- + +:Architectures: x86 +:Target: VM +:Parameters: args[0] defines the policy used when bus locks detected in guest +:Returns: 0 on success, -EINVAL when args[0] contains invalid bits + +Valid bits in args[0] are:: + + #define KVM_BUS_LOCK_DETECTION_OFF (1 << 0) + #define KVM_BUS_LOCK_DETECTION_EXIT (1 << 1) + +Enabling this capability on a VM provides userspace with a way to select +a policy to handle the bus locks detected in guest. Userspace can obtain +the supported modes from the result of KVM_CHECK_EXTENSION and define it +through the KVM_ENABLE_CAP. + +KVM_BUS_LOCK_DETECTION_OFF and KVM_BUS_LOCK_DETECTION_EXIT are supported +currently and mutually exclusive with each other. More bits can be added in +the future. + +With KVM_BUS_LOCK_DETECTION_OFF set, bus locks in guest will not cause vm exits +so that no additional actions are needed. This is the default mode. + +With KVM_BUS_LOCK_DETECTION_EXIT set, vm exits happen when bus lock detected +in VM. KVM just exits to userspace when handling them. Userspace can enforce +its own throttling or other policy based mitigations. + +This capability is aimed to address the thread that VM can exploit bus locks to +degree the performance of the whole system. Once the userspace enable this +capability and select the KVM_BUS_LOCK_DETECTION_EXIT mode, KVM will set the +KVM_RUN_BUS_LOCK flag in vcpu-run->flags field and exit to userspace. Concerning +the bus lock vm exit can be preempted by a higher priority VM exit, the exit +notifications to userspace can be KVM_EXIT_BUS_LOCK or other reasons. +KVM_RUN_BUS_LOCK flag is used to distinguish between them. + 8. Other capabilities. ====================== -- 2.11.0