[GIT PULL v1 05/10] KVM: s390: Correctly handle guest mappings without struct page

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

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.

Fixes: 5a74e3d93417 ("KVM: s390: KVM-specific bitfields and helper functions")
Fixes: a2c17f9270cc ("KVM: s390: New gmap code")
Reviewed-by: Christian Borntraeger <borntraeger@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 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