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KVM: X86: Add the Document for KVM_CAP_X86_BUS_LOCK_EXIT

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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>
This commit is contained in:
Chenyi Qiang 2020-11-06 17:03:15 +08:00 • committed by Paolo Bonzini
parent fe6b6bc802
commit c32b1b896d
1 changed files with 42 additions and 3 deletions
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45
Documentation/virt/kvm/api.rst
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@ -4893,9 +4893,11 @@ local APIC is not used.
__u16 flags; __u16 flags;
More architecture-specific flags detailing state of the VCPU that may More architecture-specific flags detailing state of the VCPU that may
affect the device's behavior. The only currently defined flag is affect the device's behavior. Current defined flags:
KVM_RUN_X86_SMM, which is valid on x86 machines and is set if the /* x86, set if the VCPU is in system management mode */
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 can then handle to implement model specific MSR handling and/or user notifications
to inform a user that an MSR was not handled. 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. 8. Other capabilities.
====================== ======================