Re: [PATCH v8 06/13] KVM: x86: Generalize private fault lookups to guest_memfd fault lookups

[Sean Christopherson <seanjc@google.com>]

On Fri, May 02, 2025, David Hildenbrand wrote:
> On 30.04.25 20:58, Ackerley Tng wrote:
> > > -	if (is_private)
> > > +	if (is_gmem)
> > >   		return max_level;
> > 
> > I think this renaming isn't quite accurate.
> 
> After our discussion yesterday, does that still hold true?

No.

> > IIUC in __kvm_mmu_max_mapping_level(), we skip considering
> > host_pfn_mapping_level() if the gfn is private because private memory
> > will not be mapped to userspace, so there's no need to query userspace
> > page tables in host_pfn_mapping_level().
> 
> I think the reason was that: for private we won't be walking the user space
> pages tables.
> 
> Once guest_memfd is also responsible for the shared part, why should this
> here still be private-only, and why should we consider querying a user space
> mapping that might not even exist?

+1, one of the big selling points for guest_memfd beyond CoCo is that it provides
guest-first memory.  It is very explicitly an intended feature that the guest
mappings KVM creates can be a superset of the host userspace mappings.  E.g. the
guest can use larger page sizes, have RW while the host has RO, etc.