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authorDavid Matlack <dmatlack@google.com>2022-12-01 11:52:49 -0800
committerPaolo Bonzini <pbonzini@redhat.com>2022-12-02 13:20:30 -0500
commit34e30ebbe48cc43c14276f863f0d2995c8f13186 (patch)
treeb67a8f87a7f9c80c56b9723f1b1fc01af1219278 /Documentation/virt
parentb8b43a4c2e9f66481cc667007aac6d0372e9c4cb (diff)
downloadlinux-34e30ebbe48cc43c14276f863f0d2995c8f13186.tar.bz2
KVM: Document the interaction between KVM_CAP_HALT_POLL and halt_poll_ns
Clarify the existing documentation about how KVM_CAP_HALT_POLL and halt_poll_ns interact to make it clear that VMs using KVM_CAP_HALT_POLL ignore halt_poll_ns. Signed-off-by: David Matlack <dmatlack@google.com> Message-Id: <20221201195249.3369720-3-dmatlack@google.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
-rw-r--r--Documentation/virt/kvm/api.rst15
-rw-r--r--Documentation/virt/kvm/halt-polling.rst13
2 files changed, 20 insertions, 8 deletions
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst
index eee9f857a986..896914e3a847 100644
--- a/Documentation/virt/kvm/api.rst
+++ b/Documentation/virt/kvm/api.rst
@@ -7213,14 +7213,13 @@ veto the transition.
:Parameters: args[0] is the maximum poll time in nanoseconds
:Returns: 0 on success; -1 on error
-This capability overrides the kvm module parameter halt_poll_ns for the
-target VM.
-
-VCPU polling allows a VCPU to poll for wakeup events instead of immediately
-scheduling during guest halts. The maximum time a VCPU can spend polling is
-controlled by the kvm module parameter halt_poll_ns. This capability allows
-the maximum halt time to specified on a per-VM basis, effectively overriding
-the module parameter for the target VM.
+KVM_CAP_HALT_POLL overrides the kvm.halt_poll_ns module parameter to set the
+maximum halt-polling time for all vCPUs in the target VM. This capability can
+be invoked at any time and any number of times to dynamically change the
+maximum halt-polling time.
+
+See Documentation/virt/kvm/halt-polling.rst for more information on halt
+polling.
7.21 KVM_CAP_X86_USER_SPACE_MSR
-------------------------------
diff --git a/Documentation/virt/kvm/halt-polling.rst b/Documentation/virt/kvm/halt-polling.rst
index 4922e4a15f18..3fae39b1a5ba 100644
--- a/Documentation/virt/kvm/halt-polling.rst
+++ b/Documentation/virt/kvm/halt-polling.rst
@@ -119,6 +119,19 @@ These module parameters can be set from the debugfs files in:
Note: that these module parameters are system wide values and are not able to
be tuned on a per vm basis.
+Any changes to these parameters will be picked up by new and existing vCPUs the
+next time they halt, with the notable exception of VMs using KVM_CAP_HALT_POLL
+(see next section).
+
+KVM_CAP_HALT_POLL
+=================
+
+KVM_CAP_HALT_POLL is a VM capability that allows userspace to override halt_poll_ns
+on a per-VM basis. VMs using KVM_CAP_HALT_POLL ignore halt_poll_ns completely (but
+still obey halt_poll_ns_grow, halt_poll_ns_grow_start, and halt_poll_ns_shrink).
+
+See Documentation/virt/kvm/api.rst for more information on this capability.
+
Further Notes
=============