Re: [PATCH v2 3/5] KVM: s390: vsie: Fix unshadowing logic

[Christian Borntraeger]

Am 12.05.26 um 19:52 schrieb Claudio Imbrenda:
> In some cases (i.e. under extreme memory pressure on the host),
> attempting to shadow memory will result in the same memory being
> unshadowed, causing a loop.
>
> Add a PGSTE bit to distinguish between shadowed memory and shadowed DAT
> tables, fix the unshadowing logic in _gmap_ptep_xchg() to prevent
> unnecessary unshadowing and perform better checks.
>
> Also fix the unshadowing logic in _gmap_crstep_xchg_atomic() which did
> not unshadow properly when the large page would become unprotected.
>
> Opportunistilcally add a check in gmap_protect_rmap() to make sure it
              ^
  Opportunistically

[...]
> +static inline bool pte_needs_unshadow(union pte oldpte, union pte newpte, union pgste pgste)
> +{
> +	if (!pgste.vsie_notif)
> +		return false;
> +	if (pgste.vsie_gmem)
> +		return (oldpte.h.p != newpte.h.p) || newpte.h.i;
> +	return !newpte.h.p || !newpte.s.pr;
> +}
> +

The newpte.s.pr part is new and seems not related to the vsie_gmem change
but I cannot find anything about this in the patch description. And I dont
understand this part. So either some explanation here, in the patch description or
a comment maybe?

>   static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, union pte newpte,
>   					  union pgste pgste, gfn_t gfn, bool needs_lock)
>   {
> @@ -180,8 +189,9 @@ static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, un
>   		pgste.prefix_notif = 0;
>   		gmap_unmap_prefix(gmap, gfn, gfn + 1);
>   	}
> -	if (pgste.vsie_notif && (ptep->h.p != newpte.h.p || newpte.h.i)) {
> +	if (pte_needs_unshadow(*ptep, newpte, pgste)) {
>   		pgste.vsie_notif = 0;
> +		pgste.vsie_gmem = 0;
>   		if (needs_lock)
>   			gmap_handle_vsie_unshadow_event(gmap, gfn);
>   		else
[...]