[PATCH v5 05/10] KVM: s390: Correctly handle guest mappings without struct page
From: Claudio Imbrenda
Date: Thu Mar 26 2026 - 09:21:58 EST
Introduce a new special softbit for large pages, like already presend
for normal pages, and use it to mark guest mappings that do not have
struct pages.
Whenever a leaf DAT entry becomes dirty, check the special softbit and
only call SetPageDirty() if there is an actual struct page.
Move the logic to mark pages dirty inside _gmap_ptep_xchg() and
_gmap_crstep_xchg_atomic(), to avoid needlessly duplicating the code.
Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
Fixes: 5a74e3d93417 ("KVM: s390: KVM-specific bitfields and helper functions")
Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Reviewed-by: Christian Borntraeger <borntraeger@xxxxxxxxxxxxx>
---
arch/s390/kvm/dat.h | 12 ++++++------
arch/s390/kvm/gmap.c | 11 ++++-------
arch/s390/kvm/gmap.h | 4 ++++
3 files changed, 14 insertions(+), 13 deletions(-)
diff --git a/arch/s390/kvm/dat.h b/arch/s390/kvm/dat.h
index efedcf96110c..874cc962e196 100644
--- a/arch/s390/kvm/dat.h
+++ b/arch/s390/kvm/dat.h
@@ -160,14 +160,14 @@ union pmd {
unsigned long :44; /* HW */
unsigned long : 3; /* Unused */
unsigned long : 1; /* HW */
+ unsigned long s : 1; /* Special */
unsigned long w : 1; /* Writable soft-bit */
unsigned long r : 1; /* Readable soft-bit */
unsigned long d : 1; /* Dirty */
unsigned long y : 1; /* Young */
- unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long : 3; /* HW */
+ unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long vsie_notif : 1; /* Referenced in a shadow table */
- unsigned long : 1; /* Unused */
unsigned long : 4; /* HW */
unsigned long sd : 1; /* Soft-Dirty */
unsigned long pr : 1; /* Present */
@@ -183,14 +183,14 @@ union pud {
unsigned long :33; /* HW */
unsigned long :14; /* Unused */
unsigned long : 1; /* HW */
+ unsigned long s : 1; /* Special */
unsigned long w : 1; /* Writable soft-bit */
unsigned long r : 1; /* Readable soft-bit */
unsigned long d : 1; /* Dirty */
unsigned long y : 1; /* Young */
- unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long : 3; /* HW */
+ unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long vsie_notif : 1; /* Referenced in a shadow table */
- unsigned long : 1; /* Unused */
unsigned long : 4; /* HW */
unsigned long sd : 1; /* Soft-Dirty */
unsigned long pr : 1; /* Present */
@@ -254,14 +254,14 @@ union crste {
struct {
unsigned long :47;
unsigned long : 1; /* HW (should be 0) */
+ unsigned long s : 1; /* Special */
unsigned long w : 1; /* Writable */
unsigned long r : 1; /* Readable */
unsigned long d : 1; /* Dirty */
unsigned long y : 1; /* Young */
- unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long : 3; /* HW */
+ unsigned long prefix_notif : 1; /* Guest prefix invalidation notification */
unsigned long vsie_notif : 1; /* Referenced in a shadow table */
- unsigned long : 1;
unsigned long : 4; /* HW */
unsigned long sd : 1; /* Soft-Dirty */
unsigned long pr : 1; /* Present */
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index 03e15b5e0b9a..c8b79ad04ac9 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -519,7 +519,7 @@ void gmap_sync_dirty_log(struct gmap *gmap, gfn_t start, gfn_t end)
_dat_walk_gfn_range(start, end, gmap->asce, &walk_ops, 0, gmap);
}
-static int gmap_handle_minor_crste_fault(union asce asce, struct guest_fault *f)
+static int gmap_handle_minor_crste_fault(struct gmap *gmap, struct guest_fault *f)
{
union crste newcrste, oldcrste = READ_ONCE(*f->crstep);
@@ -544,10 +544,8 @@ static int gmap_handle_minor_crste_fault(union asce asce, struct guest_fault *f)
newcrste.s.fc1.d = 1;
newcrste.s.fc1.sd = 1;
}
- if (!oldcrste.s.fc1.d && newcrste.s.fc1.d)
- SetPageDirty(phys_to_page(crste_origin_large(newcrste)));
/* In case of races, let the slow path deal with it. */
- return !dat_crstep_xchg_atomic(f->crstep, oldcrste, newcrste, f->gfn, asce);
+ return !gmap_crstep_xchg_atomic(gmap, f->crstep, oldcrste, newcrste, f->gfn);
}
/* Trying to write on a read-only page, let the slow path deal with it. */
return 1;
@@ -576,8 +574,6 @@ static int _gmap_handle_minor_pte_fault(struct gmap *gmap, union pgste *pgste,
newpte.s.d = 1;
newpte.s.sd = 1;
}
- if (!oldpte.s.d && newpte.s.d)
- SetPageDirty(pfn_to_page(newpte.h.pfra));
*pgste = gmap_ptep_xchg(gmap, f->ptep, newpte, *pgste, f->gfn);
return 0;
@@ -614,7 +610,7 @@ int gmap_try_fixup_minor(struct gmap *gmap, struct guest_fault *fault)
fault->callback(fault);
pgste_set_unlock(fault->ptep, pgste);
} else {
- rc = gmap_handle_minor_crste_fault(gmap->asce, fault);
+ rc = gmap_handle_minor_crste_fault(gmap, fault);
if (!rc && fault->callback)
fault->callback(fault);
}
@@ -669,6 +665,7 @@ static int _gmap_link(struct kvm_s390_mmu_cache *mc, struct gmap *gmap, int leve
oldval = READ_ONCE(*f->crstep);
newval = _crste_fc1(f->pfn, oldval.h.tt, f->writable,
f->write_attempt | oldval.s.fc1.d);
+ newval.s.fc1.s = !f->page;
newval.s.fc1.sd = oldval.s.fc1.sd;
if (oldval.val != _CRSTE_EMPTY(oldval.h.tt).val &&
crste_origin_large(oldval) != crste_origin_large(newval))
diff --git a/arch/s390/kvm/gmap.h b/arch/s390/kvm/gmap.h
index 150e91e15ee0..579399ef5480 100644
--- a/arch/s390/kvm/gmap.h
+++ b/arch/s390/kvm/gmap.h
@@ -185,6 +185,8 @@ static inline union pgste _gmap_ptep_xchg(struct gmap *gmap, union pte *ptep, un
else
_gmap_handle_vsie_unshadow_event(gmap, gfn);
}
+ if (!ptep->s.d && newpte.s.d && !newpte.s.s)
+ SetPageDirty(pfn_to_page(newpte.h.pfra));
return __dat_ptep_xchg(ptep, pgste, newpte, gfn, gmap->asce, uses_skeys(gmap));
}
@@ -220,6 +222,8 @@ static inline bool __must_check _gmap_crstep_xchg_atomic(struct gmap *gmap, unio
else
_gmap_handle_vsie_unshadow_event(gmap, gfn);
}
+ if (!oldcrste.s.fc1.d && newcrste.s.fc1.d && !newcrste.s.fc1.s)
+ SetPageDirty(phys_to_page(crste_origin_large(newcrste)));
return dat_crstep_xchg_atomic(crstep, oldcrste, newcrste, gfn, gmap->asce);
}
--
2.53.0