On Mon, Jun 17, 2024, Yan Zhao wrote:
> On Fri, Jun 14, 2024 at 04:01:07AM +0800, Edgecombe, Rick P wrote:
> > On Thu, 2024-06-13 at 14:06 +0800, Yan Zhao wrote:
> > > a) Add a condition for TDX VM type in kvm_arch_flush_shadow_memslot()
> > > besides the testing of kvm_check_has_quirk(). It is similar to
> > > "all new VM types have the quirk disabled". e.g.
> > >
> > > static inline bool kvm_memslot_flush_zap_all(struct kvm
> > > *kvm)
> > >
> > > {
> > >
> > > return kvm->arch.vm_type != KVM_X86_TDX_VM
> > > &&
> > > kvm_check_has_quirk(kvm,
> > > KVM_X86_QUIRK_SLOT_ZAP_ALL);
> > > }
> > >
> > > b) Init the disabled_quirks based on VM type in kernel, extend
> > > disabled_quirk querying/setting interface to enforce the quirk to
> > > be disabled for TDX.
There's also option:
c) Init disabled_quirks based on VM type.
I.e. let userspace enable the quirk. If the VMM wants to shoot its TDX VM guests,
then so be it. That said, I don't like this option because it would create a very
bizarre ABI.
> >
> > I'd prefer to go with option (a) here. Because we don't have any behavior
> > defined yet for KVM_X86_TDX_VM, we don't really need to "disable a quirk" of it.
I vote for (a) as well.
> > Instead we could just define KVM_X86_QUIRK_SLOT_ZAP_ALL to be about the behavior
> > of the existing vm_types. It would be a few lines of documentation to save
> > implementing and maintaining a whole interface with special logic for TDX. So to
> > me it doesn't seem worth it, unless there is some other user for a new more
> > complex quirk interface.
> What about introducing a forced disabled_quirk field?
Nah, it'd require manual opt-in for every VM type for almost no benefit. In fact,
IMO the code itself would be a net negative versus:
return kvm->arch.vm_type == KVM_X86_DEFAULT_VM &&
kvm_check_has_quirk(kvm, KVM_X86_QUIRK_SLOT_ZAP_ALL);
because explicitly checking for KVM_X86_DEFAULT_VM would directly match the
documentation (which would state that the quirk only applies to DEFAULT_VM).
