On Mon, Oct 16, 2023, Vitaly Kuznetsov wrote: > Maxim Levitsky <mlevitsk@xxxxxxxxxx> writes: > > > У вт, 2023-10-10 у 18:02 +0200, Vitaly Kuznetsov пише: > >> Hyper-V emulation in KVM is a fairly big chunk and in some cases it may be > >> desirable to not compile it in to reduce module sizes as well as attack > >> surface. Introduce CONFIG_KVM_HYPERV option to make it possible. > >> > >> Note, there's room for further nVMX/nSVM code optimizations when > >> !CONFIG_KVM_HYPERV, this will be done in follow-up patches. > > > > Maybe CONFIG_KVM_HYPERV_GUEST_SUPPORT or CONFIG_HYPERV_ON_KVM instead? > > > > IMHO CONFIG_KVM_HYPERV_GUEST_SUPPORT sounds good. Adding GUEST_SUPPORT doesn't disambiguate anything though, as there's no clear indication of whether KVM or Hyper-V is the guest. E.g. the umbrella kconfig for Linux-as-a-guest is CONFIG_HYPERVISOR_GUEST. > We already have CONFIG_KVM_XEN so I decided to stay concise. I do > understand that 'KVM-on-Hyper-V' and 'Hyper-V-on-KVM' mess which creates > the confusion though. Yeah, matching Xen is probably the best way to minimize confusion, e.g. the kernel has CONFIG_HYPERV and CONFIG_XEN to go with KVM's, CONFIG_KVM_HYPERV and CONFIG_KVM_XEN. > >> diff --git a/arch/x86/kvm/Kconfig b/arch/x86/kvm/Kconfig > >> index ed90f148140d..a06e19a8a8f6 100644 > >> --- a/arch/x86/kvm/Kconfig > >> +++ b/arch/x86/kvm/Kconfig > >> @@ -129,6 +129,15 @@ config KVM_SMM > >> > >> If unsure, say Y. > >> > >> +config KVM_HYPERV > >> + bool "Support for Microsoft Hyper-V emulation" > >> + depends on KVM > >> + default y > >> + help > >> + Provides KVM support for emulating Microsoft Hypervisor (Hyper-V). > > > > > > It feels to me that the KConfig option can have a longer description. > > > > What do you think about something like that: > > > > "Provides KVM support for emulating Microsoft Hypervisor (Hyper-V). I don't think we should put Hyper-V in parentheses, I haven't seen any documentation that calls it "Microsoft Hypervisor", i.e. Hyper-V is the full and proper name. > > This makes KVM expose a set of paravirtualized interfaces, s/makes/allows, since KVM still requires userspace to opt-in to exposing Hyper-V. > > documented in the HyperV TLFS, s/TLFS/spec? Readers that aren't already familiar with Hyper-V will have no idea what TLFS is until they click the link. > > https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs, > > which consists of a subset of paravirtualized interfaces that HyperV exposes We can trim this paragraph by stating that KVM only supports a subset of the PV interfaces straightaway. > > to its guests. E.g. Provides KVM support for for emulating Microsoft Hyper-V. This allows KVM to expose a subset of the paravirtualized interfaces defined in Hyper-V's spec: https://docs.microsoft.com/en-us/virtualization/hyper-v-on-windows/reference/tlfs. > > > > This improves performance of modern Windows guests. Isn't Hyper-V emulation effectively mandatory these days? IIRC, modern versions of Windows will fail to boot if they detect a hypervisor but the core Hyper-V interfaces aren't supported.
