Re: [PATCH v2 1/6] KVM: x86/mmu: add a new mmu zap helper to indicate memtype changes

Yan Zhao
2023-05-31T00:44:06Z

On Tue, May 30, 2023 at 04:51:25PM -0700, Sean Christopherson wrote:
> On Tue, May 30, 2023, Yan Zhao wrote:
> > On Thu, May 25, 2023 at 08:54:15AM -0700, Sean Christopherson wrote:
> > And I combined the __kvm_mmu_honors_guest_mtrrs() into
> > kvm_mmu_honors_guest_mtrrs(). Not sure if you like it :)
>
> I would prefer to provide a separater inner helper, mainly so that the common
> case callers don't need to pass %false. I don't love passing bools, but it's
> tolerable for a one-off use of an inner helper.

Ok. Will follow this way.
It's reasonable :)

> > +/*
> > + * Returns if KVM honors guest MTRRs
> > + * @override_vm_has_noncoherent_dma: Allow caller to override non-coherent DMA
> > + * status returned from
> > + * kvm_arch_has_noncoherent_dma()
> > + */
> > +bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm,
> > + bool override_vm_has_noncoherent_dma)
> > +{
> > + bool noncoherent_dma = override_vm_has_noncoherent_dma ? true :
> > + kvm_arch_has_noncoherent_dma(kvm);
>
> The "override" name is confusing, e.g. it won't be clear when it's safe/correct
> for a new caller to override kvm_arch_has_noncoherent_dma(). If we go with a
> single helper, I could live with:
>
> bool kvm_mmu_honors_guest_mtrrs(struct kvm *kvm, bool stopping_noncoherent_dma)
> {
> bool noncoherent_dma = stopping_noncoherent_dma ||
> kvm_arch_has_noncoherent_dma(kvm);
>
> ...
> }
>
> but that makes it awkward to use common code for start+stop assignment, and as
> above there are three "normal" callers that would have to pass magic %false
> values regardless of the name.