Re: [PATCH v10 07/41] KVM: guest_memfd: Stub in ability to enable in-place shared<=>private conversion

[Sean Christopherson]

On Wed, Aug 12, 2026, David Hildenbrand (Arm) wrote:
> On 8/10/26 17:01, Sean Christopherson wrote:
> > On Mon, Aug 10, 2026, David Hildenbrand (Arm) wrote:
> >> On 8/7/26 23:52, Ackerley Tng via B4 Relay wrote:
> >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >>> index 65fbce46b63f4..9477ecebbbced 100644
> >>> --- a/include/linux/kvm_host.h
> >>> +++ b/include/linux/kvm_host.h
> >>> @@ -2580,6 +2580,8 @@ static inline bool kvm_vm_mem_is_private(struct kvm *kvm, gfn_t gfn)
> >>>  #endif  /* CONFIG_KVM_VM_MEMORY_ATTRIBUTES */
> >>>  
> >>>  #ifdef kvm_arch_has_private_mem
> >>> +extern bool gmem_in_place_conversion;
> >>
> >> Is there a "supports/has/enable" in there? And should we call it "kvm_gmem" for
> >> completeness?
> > 
> > It's kinda stupid and definitely more than a bit inconsistent, but overall I think
> > I actually like "gmem_in_place_conversion" the best.
> > 
> > gmem_has_in_place_conversion and gmem_supports_in_place_conversion are misleading
> > because it's not just that guest_memfd has/supports in-place conversion, it's that
> > that KVM is tracking PRIVATE in guest_memfd and so in-place conversion is the only
> > option.
> > 
> > On the other hand, while gmem_in_place_conversion_enabled is better, it's not
> > quite accurate either because userspace isn't strictly required to do in-place
> > conversion.
> > 
> > As for a kvm_ prefix, IMO gmem_ is sufficient for a namespace, and not having kvm_
> > is consistent with most module params in KVM.
> 
> Maybe we should have a helper function instead of accessing the module parameter
> directly, then the gmem_in_place_conversion could just stay file-local and
> kvm_gmem_in_place_conversion() would be used by other code that wants to obtain
> the value.
> 
> Instead of the
> 
> #define mem_in_place_conversion false
> 
> We'd have
> 
> #define kvm_gmem_in_place_conversion()	false
> 
> just a thought ...

FWIW, I'd rather prefix kvm_ than add a wrapper to get a boolean.