KVM: s390: KVM page table management functions: clear and replace

Add page table management functions to be used for KVM guest (gmap)
page tables.

This patch adds functions to clear, replace or exchange DAT table
entries.

Acked-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

arch/s390/kvm/dat.c

@@ -101,3 +101,118 @@ void dat_free_level(struct crst_table *table, bool owns_ptes)
 	}
 	dat_free_crst(table);
 }
+
+/**
+ * dat_crstep_xchg() - Exchange a gmap CRSTE with another.
+ * @crstep: Pointer to the CRST entry
+ * @new: Replacement entry.
+ * @gfn: The affected guest address.
+ * @asce: The ASCE of the address space.
+ *
+ * Context: This function is assumed to be called with kvm->mmu_lock held.
+ */
+void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce asce)
+{
+	if (crstep->h.i) {
+		WRITE_ONCE(*crstep, new);
+		return;
+	} else if (cpu_has_edat2()) {
+		crdte_crste(crstep, *crstep, new, gfn, asce);
+		return;
+	}
+
+	if (machine_has_tlb_guest())
+		idte_crste(crstep, gfn, IDTE_GUEST_ASCE, asce, IDTE_GLOBAL);
+	else
+		idte_crste(crstep, gfn, 0, NULL_ASCE, IDTE_GLOBAL);
+	WRITE_ONCE(*crstep, new);
+}
+
+/**
+ * dat_crstep_xchg_atomic() - Atomically exchange a gmap CRSTE with another.
+ * @crstep: Pointer to the CRST entry.
+ * @old: Expected old value.
+ * @new: Replacement entry.
+ * @gfn: The affected guest address.
+ * @asce: The asce of the address space.
+ *
+ * This function is needed to atomically exchange a CRSTE that potentially
+ * maps a prefix area, without having to invalidate it inbetween.
+ *
+ * Context: This function is assumed to be called with kvm->mmu_lock held.
+ *
+ * Return: %true if the exchange was successful.
+ */
+bool dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste new, gfn_t gfn,
+			    union asce asce)
+{
+	if (old.h.i)
+		return arch_try_cmpxchg((long *)crstep, &old.val, new.val);
+	if (cpu_has_edat2())
+		return crdte_crste(crstep, old, new, gfn, asce);
+	return cspg_crste(crstep, old, new);
+}
+
+static void dat_set_storage_key_from_pgste(union pte pte, union pgste pgste)
+{
+	union skey nkey = { .acc = pgste.acc, .fp = pgste.fp };
+
+	page_set_storage_key(pte_origin(pte), nkey.skey, 0);
+}
+
+static void dat_move_storage_key(union pte old, union pte new)
+{
+	page_set_storage_key(pte_origin(new), page_get_storage_key(pte_origin(old)), 1);
+}
+
+static union pgste dat_save_storage_key_into_pgste(union pte pte, union pgste pgste)
+{
+	union skey skey;
+
+	skey.skey = page_get_storage_key(pte_origin(pte));
+
+	pgste.acc = skey.acc;
+	pgste.fp = skey.fp;
+	pgste.gr |= skey.r;
+	pgste.gc |= skey.c;
+
+	return pgste;
+}
+
+union pgste __dat_ptep_xchg(union pte *ptep, union pgste pgste, union pte new, gfn_t gfn,
+			    union asce asce, bool uses_skeys)
+{
+	union pte old = READ_ONCE(*ptep);
+
+	/* Updating only the software bits while holding the pgste lock. */
+	if (!((ptep->val ^ new.val) & ~_PAGE_SW_BITS)) {
+		WRITE_ONCE(ptep->swbyte, new.swbyte);
+		return pgste;
+	}
+
+	if (!old.h.i) {
+		unsigned long opts = IPTE_GUEST_ASCE | (pgste.nodat ? IPTE_NODAT : 0);
+
+		if (machine_has_tlb_guest())
+			__ptep_ipte(gfn_to_gpa(gfn), (void *)ptep, opts, asce.val, IPTE_GLOBAL);
+		else
+			__ptep_ipte(gfn_to_gpa(gfn), (void *)ptep, 0, 0, IPTE_GLOBAL);
+	}
+
+	if (uses_skeys) {
+		if (old.h.i && !new.h.i)
+			/* Invalid to valid: restore storage keys from PGSTE. */
+			dat_set_storage_key_from_pgste(new, pgste);
+		else if (!old.h.i && new.h.i)
+			/* Valid to invalid: save storage keys to PGSTE. */
+			pgste = dat_save_storage_key_into_pgste(old, pgste);
+		else if (!old.h.i && !new.h.i)
+			/* Valid to valid: move storage keys. */
+			if (old.h.pfra != new.h.pfra)
+				dat_move_storage_key(old, new);
+		/* Invalid to invalid: nothing to do. */
+	}
+
+	WRITE_ONCE(*ptep, new);
+	return pgste;
+}

arch/s390/kvm/dat.h

@@ -430,6 +430,12 @@ struct kvm_s390_mmu_cache {
 	short int n_rmaps;
 };
 
+union pgste __must_check __dat_ptep_xchg(union pte *ptep, union pgste pgste, union pte new,
+					 gfn_t gfn, union asce asce, bool uses_skeys);
+bool dat_crstep_xchg_atomic(union crste *crstep, union crste old, union crste new, gfn_t gfn,
+			    union asce asce);
+void dat_crstep_xchg(union crste *crstep, union crste new, gfn_t gfn, union asce asce);
+
 void dat_free_level(struct crst_table *table, bool owns_ptes);
 struct crst_table *dat_alloc_crst_sleepable(unsigned long init);
 
@@ -757,6 +763,21 @@ static inline void pgste_set_unlock(union pte *ptep, union pgste pgste)
 	WRITE_ONCE(*pgste_of(ptep), pgste);
 }
 
+static inline void dat_ptep_xchg(union pte *ptep, union pte new, gfn_t gfn, union asce asce,
+				 bool has_skeys)
+{
+	union pgste pgste;
+
+	pgste = pgste_get_lock(ptep);
+	pgste = __dat_ptep_xchg(ptep, pgste, new, gfn, asce, has_skeys);
+	pgste_set_unlock(ptep, pgste);
+}
+
+static inline void dat_ptep_clear(union pte *ptep, gfn_t gfn, union asce asce, bool has_skeys)
+{
+	dat_ptep_xchg(ptep, _PTE_EMPTY, gfn, asce, has_skeys);
+}
+
 static inline void dat_free_pt(struct page_table *pt)
 {
 	free_page((unsigned long)pt);
@@ -794,4 +815,23 @@ static inline struct kvm_s390_mmu_cache *kvm_s390_new_mmu_cache(void)
 	return NULL;
 }
 
+static inline bool dat_pmdp_xchg_atomic(union pmd *pmdp, union pmd old, union pmd new,
+					gfn_t gfn, union asce asce)
+{
+	return dat_crstep_xchg_atomic(_CRSTEP(pmdp), _CRSTE(old), _CRSTE(new), gfn, asce);
+}
+
+static inline bool dat_pudp_xchg_atomic(union pud *pudp, union pud old, union pud new,
+					gfn_t gfn, union asce asce)
+{
+	return dat_crstep_xchg_atomic(_CRSTEP(pudp), _CRSTE(old), _CRSTE(new), gfn, asce);
+}
+
+static inline void dat_crstep_clear(union crste *crstep, gfn_t gfn, union asce asce)
+{
+	union crste newcrste = _CRSTE_EMPTY(crstep->h.tt);
+
+	dat_crstep_xchg(crstep, newcrste, gfn, asce);
+}
+
 #endif /* __KVM_S390_DAT_H */