Re: [RFC PATCH 1/3] KVM: guest_memfd: Use memslot id to keep track of associated memslots

[Sean Christopherson <seanjc@google.com>]

On Mon, Jul 06, 2026, Alexandru Elisei wrote:
> On Mon, Jul 06, 2026 at 09:14:59AM +0200, David Hildenbrand wrote:
> > > diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> > > index db57c5766ab6..43ef8e908aaf 100644
> > > --- a/virt/kvm/guest_memfd.c
> > > +++ b/virt/kvm/guest_memfd.c
> > > @@ -25,6 +25,7 @@ struct gmem_file {
> > >  	struct kvm *kvm;
> > >  	struct xarray bindings;
> > >  	struct list_head entry;
> > > +	bool found_memslot;	/* Used for balancing invalidations when punching a hole */
> > 
> > Probabably best to document what it means, not only what it is used for (and
> > maybe document above the member if you end up with more text).
> 
> Sure, this is how I changed it:
> 
> diff --git a/virt/kvm/guest_memfd.c b/virt/kvm/guest_memfd.c
> index 210bdd76f0aa..3cee64047bce 100644
> --- a/virt/kvm/guest_memfd.c
> +++ b/virt/kvm/guest_memfd.c
> @@ -25,7 +25,13 @@ struct gmem_file {
>         struct kvm *kvm;
>         struct xarray bindings;
>         struct list_head entry;
> -       bool found_memslot;     /* Used for balancing invalidations when punching a hole */
> +       /*
> +        * Keeps track of whether memory has been unmapped during secondary MMU
> +        * invalidation, to keep the invalidate start and end calls balanced.
> +        *
> +        * Accessed while holding the inode->i_mapping lock in exclusive mode.
> +        */
> +       bool memslot_invalidated;
>  };
> 
> Hopefully the new name is better.

Why add a boolean?  It's not _needed_ to balance updates, or rather it shouldn't
be needed.  filemap_invalidate_lock() prevents modifying bindings while an
invalidation is in-progress.  It might be a performation optimization, but if so,
it's a premature one and belongs in a separate patch.