KVM/Hyper-V: Add new KVM capability KVM_CAP_HYPERV_DIRECT_TLBFLUSH

Hyper-V direct tlb flush function should be enabled for
guest that only uses Hyper-V hypercall. User space
hypervisor(e.g, Qemu) can disable KVM identification in
CPUID and just exposes Hyper-V identification to make
sure the precondition. Add new KVM capability KVM_CAP_
HYPERV_DIRECT_TLBFLUSH for user space to enable Hyper-V
direct tlb function and this function is default to be
disabled in KVM.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/Documentation/virt/kvm/api.txt b/Documentation/virt/kvm/api.txt
index 136f1eef3712d3b3205c43a61b4c6e78c69d3e28..4833904d32a5aae880186f47266738cdcd44989d 100644 (file)
--- a/Documentation/virt/kvm/api.txt
+++ b/Documentation/virt/kvm/api.txt
@@ -5309,3 +5309,16 @@ Architectures: x86
 This capability indicates that KVM supports paravirtualized Hyper-V IPI send
 hypercalls:
 HvCallSendSyntheticClusterIpi, HvCallSendSyntheticClusterIpiEx.
+8.21 KVM_CAP_HYPERV_DIRECT_TLBFLUSH
+
+Architecture: x86
+
+This capability indicates that KVM running on top of Hyper-V hypervisor
+enables Direct TLB flush for its guests meaning that TLB flush
+hypercalls are handled by Level 0 hypervisor (Hyper-V) bypassing KVM.
+Due to the different ABI for hypercall parameters between Hyper-V and
+KVM, enabling this capability effectively disables all hypercall
+handling by KVM (as some KVM hypercall may be mistakenly treated as TLB
+flush hypercalls by Hyper-V) so userspace should disable KVM identification
+in CPUID and only exposes Hyper-V identification. In this case, guest
+thinks it's running on Hyper-V and only use Hyper-V hypercalls.

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a3a3ec73fa2f858073bf0eeadb7b89574093bc69..4765ae0fc50689973e572f54e69cea385ac4cc98 100644 (file)
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1213,6 +1213,7 @@ struct kvm_x86_ops {
        bool (*need_emulation_on_page_fault)(struct kvm_vcpu *vcpu);
 
        bool (*apic_init_signal_blocked)(struct kvm_vcpu *vcpu);
+       int (*enable_direct_tlbflush)(struct kvm_vcpu *vcpu);
 };
 
 struct kvm_arch_async_pf {

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index bb93771e4170f090cda4a93edaa9580ed1c321fd..5becc6753280063a26594aaf77d8fedfc91a49d3 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3282,6 +3282,9 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
                r = kvm_x86_ops->get_nested_state ?
                        kvm_x86_ops->get_nested_state(NULL, NULL, 0) : 0;
                break;
+       case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
+               r = kvm_x86_ops->enable_direct_tlbflush ? 1 : 0;
+               break;
        default:
                break;
        }
@@ -4055,6 +4058,11 @@ static int kvm_vcpu_ioctl_enable_cap(struct kvm_vcpu *vcpu,
                                r = -EFAULT;
                }
                return r;
+       case KVM_CAP_HYPERV_DIRECT_TLBFLUSH:
+               if (!kvm_x86_ops->enable_direct_tlbflush)
+                       return -ENOTTY;
+
+               return kvm_x86_ops->enable_direct_tlbflush(vcpu);
 
        default:
                return -EINVAL;

diff --git a/include/uapi/linux/kvm.h b/include/uapi/linux/kvm.h
index 233efbb1c81ca153c64693814d8518756284e1d0..c73aead0c0a8a4d8472a140e89e69cc6b96015e4 100644 (file)
--- a/include/uapi/linux/kvm.h
+++ b/include/uapi/linux/kvm.h
@@ -999,6 +999,7 @@ struct kvm_ppc_resize_hpt {
 #define KVM_CAP_ARM_PTRAUTH_GENERIC 172
 #define KVM_CAP_PMU_EVENT_FILTER 173
 #define KVM_CAP_ARM_IRQ_LINE_LAYOUT_2 174
+#define KVM_CAP_HYPERV_DIRECT_TLBFLUSH 175
 
 #ifdef KVM_CAP_IRQ_ROUTING