From 9029496abfae3c208336855ae6f3e1f5f881ef76 Mon Sep 17 00:00:00 2001 From: Claudio Imbrenda Date: Tue, 19 May 2026 17:01:14 +0200 Subject: [PATCH] KVM: s390: Properly reset zero bit in PGSTE In case of memory pressure, it's possible that a guest page gets freed and then almost immediately reused by the guest. If CMMA is enabled, _essa_clear_cbrl() will discard all pages that are either unused or zero. If a discarded page is reused before _essa_clear_cbrl() is called, and the pgste.zero bit is not cleared, the page will be discarded despite not being unused. When calling _gmap_ptep_xchg(), always clear the pgste.zero bit. This prevents the page from being accidentally discarded when not unused. Signed-off-by: Claudio Imbrenda Fixes: a2c17f9270cc ("KVM: s390: New gmap code") Reviewed-by: Steffen Eiden Signed-off-by: Christian Borntraeger --- arch/s390/kvm/gmap.h | 1 + 1 file changed, 1 insertion(+) diff --git a/arch/s390/kvm/gmap.h b/arch/s390/kvm/gmap.h index 6e51ec6066b4..742e42a31744 100644 --- a/arch/s390/kvm/gmap.h +++ b/arch/s390/kvm/gmap.h @@ -220,6 +220,7 @@ static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, un } if (!ptep->s.d && newpte.s.d && !newpte.s.s) SetPageDirty(pfn_to_page(newpte.h.pfra)); + pgste.zero = 0; return __dat_ptep_xchg(ptep, pgste, newpte, gfn, gmap->asce, uses_skeys(gmap)); }