lantianyu1986@gmail.com writes:

From: Tianyu Lan <redacted>

This patchset is to add Hyper-V direct tlb support in KVM. Hyper-V
in L0 can delegate L1 hypervisor to handle tlb flush request from
L2 guest when direct tlb flush is enabled in L1.

Patch 2 introduces new cap KVM_CAP_HYPERV_DIRECT_TLBFLUSH to enable
feature from user space. User space should enable this feature only
when Hyper-V hypervisor capability is exposed to guest and KVM profile
is hided. There is a parameter conflict between KVM and Hyper-V hypercall.
We hope L2 guest doesn't use KVM hypercall when the feature is
enabled. Detail please see comment of new API
"KVM_CAP_HYPERV_DIRECT_TLBFLUSH"

I was thinking about this for awhile and I think I have a better
proposal. Instead of adding this new capability let's enable direct TLB
flush when KVM guest enables Hyper-V Hypercall page (writes to
HV_X64_MSR_HYPERCALL) - this guarantees that the guest doesn't need KVM
hypercalls as we can't handle both KVM-style and Hyper-V-style
hypercalls simultaneously and kvm_emulate_hypercall() does:

	if (kvm_hv_hypercall_enabled(vcpu->kvm))
		return kvm_hv_hypercall(vcpu);

What do you think?

(and instead of adding the capability we can add kvm.ko module parameter
to enable direct tlb flush unconditionally, like
'hv_direct_tlbflush=-1/0/1' with '-1' being the default (autoselect
based on Hyper-V hypercall enablement, '0' - permanently disabled, '1' -
permanenetly enabled)).

-- 
Vitaly