Nikolas Wipper nikwip@amazon.de writes:
Add API documentation for the new KVM_HYPERV_SET_TLB_FLUSH_INHIBIT ioctl.
Signed-off-by: Nikolas Wipper nikwip@amazon.de
Documentation/virt/kvm/api.rst | 41 ++++++++++++++++++++++++++++++++++ 1 file changed, 41 insertions(+)
diff --git a/Documentation/virt/kvm/api.rst b/Documentation/virt/kvm/api.rst index a4b7dc4a9dda..9c11a8af336b 100644 --- a/Documentation/virt/kvm/api.rst +++ b/Documentation/virt/kvm/api.rst @@ -6443,6 +6443,47 @@ the capability to be present. `flags` must currently be zero. +4.144 KVM_HYPERV_SET_TLB_FLUSH_INHIBIT +--------------------------------------
+:Capability: KVM_CAP_HYPERV_TLB_FLUSH_INHIBIT +:Architectures: x86 +:Type: vcpu ioctl +:Parameters: struct kvm_hyperv_tlb_flush_inhibit +:returnReturns: 0 on success, this ioctl can't fail
+KVM_HYPERV_SET_TLB_FLUSH_INHIBIT allows userspace to prevent Hyper-V hyper-calls
Very minor nitpick: I suggest standardize on "hypercall" spelling without the dash because:
$ grep -c hypercall Documentation/virt/kvm/api.rst 56 $ grep -c hyper-call Documentation/virt/kvm/api.rst 3
(I see all three 'hypercall', 'hyper-call', 'hyper call' usages in the wild and I honestly don't think it matters but it would be nice to adhere to one share across the same file / KVM docs).
+that remotely flush a vCPU's TLB, i.e. HvFlushVirtualAddressSpace(Ex)/ +HvFlushVirtualAddressList(Ex). When the flag is set, a vCPU attempting to flush +an inhibited vCPU will be suspended and will only resume once the flag is +cleared again using this ioctl. During suspension, the vCPU will not finish the +hyper-call, but may enter the guest to retry it. Because it is caused by a +hyper-call, the suspension naturally happens on a guest instruction boundary. +This behaviour and the suspend state itself are specified in Microsoft's +"Hypervisor Top Level Functional Specification" (TLFS).
+::
- /* for KVM_HYPERV_SET_TLB_FLUSH_INHIBIT */
- struct kvm_hyperv_tlb_flush_inhibit {
/* in */__u16 flags;- #define KVM_HYPERV_UNINHIBIT_TLB_FLUSH 0
- #define KVM_HYPERV_INHIBIT_TLB_FLUSH 1
__u8 inhibit;__u8 padding[5];- };
+No flags are specified so far, the corresponding field must be set to zero, +otherwise the ioctl will fail with exit code -EINVAL.
+The suspension is transparent to userspace. It won't cause KVM_RUN to return or +the MP state to be changed. The suspension cannot be manually induced or exited +apart from changing the TLB flush inhibit flag of a targeted processor.
+There is no way for userspace to query the state of the flush inhibit flag. +Userspace must keep track of the required state itself.
- The kvm_run structure
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