Sean Christopherson <seanjc@xxxxxxxxxx> writes: > On Fri, Sep 09, 2022, Vitaly Kuznetsov wrote: ... >> While this certainly looks like an overkill here, we could probably add >> new, VMM-spefific CPUID leaves to KVM, e.g. >> >> 0x4000000A: VMM signature >> 0x4000000B: VMM features >> 0x4000000C: VMM quirks >> ... >> >> this way VMMs (like QEMU) could identify themselves and suggest VMM >> specific things to guests without KVM's involvement. Just if 'fw_cfg' is >> not enough) > > I don't think KVM needs to get involved in that either. The de facto hypervisor > CPUID standard already allows for multiple hypervisors/VMMs to announce themselves > to the guest, e.g. QEMU could add itself as another VMM using 0x40000100 (shifted > as necessary to accomodate KVM+Hyper-V). True, VMM can just use another hypervisor space (+0x100) but we can view it from a slightly different angle: KVM itself is insufficient to run VMs, there's always a VMM in the background, we may want to provide a "standard" for its information meaning guests won't need to search for VMMs signature[s] but can directly refer to "standardized" leaves. (All this is a purely theoretical discussion at this point, we need a good reason to introduce this first). -- Vitaly
