[PATCH v3 1/5] KVM: s390: Track page size in struct guest_fault

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

Until now, the members of struct guest_fault are always accessed while
holding the required locks, and thus the ptep and crstep pointers can
be dereferenced safely.

There will be some new cases where callers of kvm_s390_faultin_gfn()
need to know the size of the page used to solve the fault, at which
point no locks are held anymore, and dereferencing the crstep field
is not possible.

Introduce a new crste_region3 flag for struct guest_fault to indicate
whether the crstep used to solve the fault was a region 3 entry with FC=1
(large pud).

This allows to disambiguate all three possible scenarios:
* If ptep is not NULL, the fault was solved with a pte.
* If ptep is NULL and crste_region3 is 0, a segment entry with FC=1
  (large pmd) was used.
* If ptep is NULL and crste_region3 is 1, a region 3 entry with FC=1
  (large pud) was used.

Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
---
 arch/s390/kvm/dat.h  | 1 +
 arch/s390/kvm/gmap.c | 2 ++
 2 files changed, 3 insertions(+)

diff --git a/arch/s390/kvm/dat.h b/arch/s390/kvm/dat.h
index 8f8278c44879..5d848e74e382 100644
--- a/arch/s390/kvm/dat.h
+++ b/arch/s390/kvm/dat.h
@@ -500,6 +500,7 @@ struct guest_fault {
 	bool write_attempt;	/* Write access attempted */
 	bool attempt_pfault;	/* Attempt a pfault first */
 	bool valid;		/* This entry contains valid data */
+	bool crste_region3;     /* Whether crstep refers to a region3 entry */
 	void (*callback)(struct guest_fault *f);
 	void *priv;
 };
diff --git a/arch/s390/kvm/gmap.c b/arch/s390/kvm/gmap.c
index 3c26e35af0ef..fe138d17caaf 100644
--- a/arch/s390/kvm/gmap.c
+++ b/arch/s390/kvm/gmap.c
@@ -531,6 +531,7 @@ static int gmap_handle_minor_crste_fault(struct gmap *gmap, struct guest_fault *
 	f->pfn = PHYS_PFN(large_crste_to_phys(oldcrste, f->gfn));
 	f->writable = oldcrste.s.fc1.w;
 
+	f->crste_region3 = is_pud(oldcrste);
 	/* Appropriate permissions already (race with another handler), nothing to do. */
 	if (!oldcrste.h.i && !(f->write_attempt && oldcrste.h.p))
 		return 0;
@@ -690,6 +691,7 @@ static int _gmap_link(struct kvm_s390_mmu_cache *mc, struct gmap *gmap, int leve
 			if (oldval.val != _CRSTE_EMPTY(oldval.h.tt).val &&
 			    crste_origin_large(oldval) != crste_origin_large(newval))
 				return -EAGAIN;
+			f->crste_region3 = is_pud(newval);
 		} while (!gmap_crstep_xchg_atomic(gmap, f->crstep, oldval, newval, f->gfn));
 		if (f->callback)
 			f->callback(f);
-- 
2.54.0