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authorChenyi Qiang <chenyi.qiang@intel.com>2020-11-06 12:03:15 +0300
committerPaolo Bonzini <pbonzini@redhat.com>2021-02-04 13:27:22 +0300
commitc32b1b896d2ab30ac30bc39194bac47a09f7f497 (patch)
treea688f15ef61ddc589d3bf2860f375b865bc98abc /Documentation/virt
parentfe6b6bc802b40081e8a7a1abe8d32b88d10a03e1 (diff)
downloadlinux-c32b1b896d2ab30ac30bc39194bac47a09f7f497.tar.xz
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 <chenyi.qiang@intel.com> Message-Id: <20201106090315.18606-5-chenyi.qiang@intel.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
-rw-r--r--Documentation/virt/kvm/api.rst45
1 files 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.
======================