Re: [PATCH v1 13/13] KVM: s390: remove the last user of page->index

[Claudio Imbrenda <imbrenda@linux.ibm.com>]

On Mon, 20 Jan 2025 10:43:15 +0100
David Hildenbrand <david@redhat.com> wrote:

> >> +static inline unsigned long gmap_pgste_get_index(unsigned long *pgt)
> >> +{
> >> +	unsigned long *pgstes, res;
> >> +
> >> +	pgstes = pgt + _PAGE_ENTRIES;
> >> +
> >> +	res = (pgstes[0] & PGSTE_ST2_MASK) << 16;
> >> +	res |= pgstes[1] & PGSTE_ST2_MASK;
> >> +	res |= (pgstes[2] & PGSTE_ST2_MASK) >> 16;
> >> +	res |= (pgstes[3] & PGSTE_ST2_MASK) >> 32;
> >> +
> >> +	return res;
> >> +}  
> > 
> > I have to think about that change for a bit before I post an opinion.  
> 
> I'm wondering if we should just do what Willy suggested and use ptdesc 
> -> pt_index instead?  

we will need to store more stuff in the future; putting things in the
PGSTEs gives us 512 bytes per table (although I admit it looks... weird)

> 
> It's not like we must "force" this removal here. If we'll simply 
> allocate a ptdesc memdesc in the future for these page tables (just like 
> for any other page table), we have that extra space easily available.
> 
> The important part is getting rid of page->index now, but not 
> necessarily ptdesc->pt_index.
>