KVM: s390: extend kvm_s390_shadow_fault to return entry pointer

Extend kvm_s390_shadow_fault to return the pointer to the valid leaf
DAT table entry, or to the invalid entry.

Also return some flags in the lower bits of the address:
PEI_DAT_PROT: indicates that DAT protection applies because of the
              protection bit in the segment (or, if EDAT, region) tables.
PEI_NOT_PTE: indicates that the address of the DAT table entry returned
             does not refer to a PTE, but to a segment or region table.
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Cc: stable@vger.kernel.org
Reviewed-by: Janosch Frank <frankja@de.ibm.com>
Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Christian Borntraeger <borntraeger@de.ibm.com>
Link: https://lore.kernel.org/r/20210302174443.514363-3-imbrenda@linux.ibm.com
[borntraeger@de.ibm.com: fold in a fix from Claudio]
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

arch/s390/kvm/gaccess.c

@@ -976,7 +976,9 @@ int kvm_s390_check_low_addr_prot_real(struct kvm_vcpu *vcpu, unsigned long gra)
  * kvm_s390_shadow_tables - walk the guest page table and create shadow tables
  * @sg: pointer to the shadow guest address space structure
  * @saddr: faulting address in the shadow gmap
- * @pgt: pointer to the page table address result
+ * @pgt: pointer to the beginning of the page table for the given address if
+ *	 successful (return value 0), or to the first invalid DAT entry in
+ *	 case of exceptions (return value > 0)
  * @fake: pgt references contiguous guest memory block, not a pgtable
  */
 static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
@@ -1034,6 +1036,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 			rfte.val = ptr;
 			goto shadow_r2t;
 		}
+		*pgt = ptr + vaddr.rfx * 8;
 		rc = gmap_read_table(parent, ptr + vaddr.rfx * 8, &rfte.val);
 		if (rc)
 			return rc;
@@ -1060,6 +1063,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 			rste.val = ptr;
 			goto shadow_r3t;
 		}
+		*pgt = ptr + vaddr.rsx * 8;
 		rc = gmap_read_table(parent, ptr + vaddr.rsx * 8, &rste.val);
 		if (rc)
 			return rc;
@@ -1087,6 +1091,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 			rtte.val = ptr;
 			goto shadow_sgt;
 		}
+		*pgt = ptr + vaddr.rtx * 8;
 		rc = gmap_read_table(parent, ptr + vaddr.rtx * 8, &rtte.val);
 		if (rc)
 			return rc;
@@ -1123,6 +1128,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 			ste.val = ptr;
 			goto shadow_pgt;
 		}
+		*pgt = ptr + vaddr.sx * 8;
 		rc = gmap_read_table(parent, ptr + vaddr.sx * 8, &ste.val);
 		if (rc)
 			return rc;
@@ -1157,6 +1163,8 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
  * @vcpu: virtual cpu
  * @sg: pointer to the shadow guest address space structure
  * @saddr: faulting address in the shadow gmap
+ * @datptr: will contain the address of the faulting DAT table entry, or of
+ *	    the valid leaf, plus some flags
  *
  * Returns: - 0 if the shadow fault was successfully resolved
  *	    - > 0 (pgm exception code) on exceptions while faulting
@@ -1165,11 +1173,11 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
  *	    - -ENOMEM if out of memory
  */
 int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg,
-			  unsigned long saddr)
+			  unsigned long saddr, unsigned long *datptr)
 {
 	union vaddress vaddr;
 	union page_table_entry pte;
-	unsigned long pgt;
+	unsigned long pgt = 0;
 	int dat_protection, fake;
 	int rc;
 
@@ -1191,8 +1199,20 @@ int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *sg,
 		pte.val = pgt + vaddr.px * PAGE_SIZE;
 		goto shadow_page;
 	}
-	if (!rc)
-		rc = gmap_read_table(sg->parent, pgt + vaddr.px * 8, &pte.val);
+
+	switch (rc) {
+	case PGM_SEGMENT_TRANSLATION:
+	case PGM_REGION_THIRD_TRANS:
+	case PGM_REGION_SECOND_TRANS:
+	case PGM_REGION_FIRST_TRANS:
+		pgt |= PEI_NOT_PTE;
+		break;
+	case 0:
+		pgt += vaddr.px * 8;
+		rc = gmap_read_table(sg->parent, pgt, &pte.val);
+	}
+	if (datptr)
+		*datptr = pgt | dat_protection * PEI_DAT_PROT;
 	if (!rc && pte.i)
 		rc = PGM_PAGE_TRANSLATION;
 	if (!rc && pte.z)

arch/s390/kvm/gaccess.h

@@ -376,7 +376,11 @@ void ipte_unlock(struct kvm_vcpu *vcpu);
 int ipte_lock_held(struct kvm_vcpu *vcpu);
 int kvm_s390_check_low_addr_prot_real(struct kvm_vcpu *vcpu, unsigned long gra);
 
+/* MVPG PEI indication bits */
+#define PEI_DAT_PROT 2
+#define PEI_NOT_PTE 4
+
 int kvm_s390_shadow_fault(struct kvm_vcpu *vcpu, struct gmap *shadow,
-			  unsigned long saddr);
+			  unsigned long saddr, unsigned long *datptr);
 
 #endif /* __KVM_S390_GACCESS_H */

arch/s390/kvm/vsie.c

@@ -620,10 +620,10 @@ static int map_prefix(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 	/* with mso/msl, the prefix lies at offset *mso* */
 	prefix += scb_s->mso;
 
-	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, prefix);
+	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap, prefix, NULL);
 	if (!rc && (scb_s->ecb & ECB_TE))
 		rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
-					   prefix + PAGE_SIZE);
+					   prefix + PAGE_SIZE, NULL);
 	/*
 	 * We don't have to mprotect, we will be called for all unshadows.
 	 * SIE will detect if protection applies and trigger a validity.
@@ -914,7 +914,7 @@ static int handle_fault(struct kvm_vcpu *vcpu, struct vsie_page *vsie_page)
 				    current->thread.gmap_addr, 1);
 
 	rc = kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
-				   current->thread.gmap_addr);
+				   current->thread.gmap_addr, NULL);
 	if (rc > 0) {
 		rc = inject_fault(vcpu, rc,
 				  current->thread.gmap_addr,
@@ -936,7 +936,7 @@ static void handle_last_fault(struct kvm_vcpu *vcpu,
 {
 	if (vsie_page->fault_addr)
 		kvm_s390_shadow_fault(vcpu, vsie_page->gmap,
-				      vsie_page->fault_addr);
+				      vsie_page->fault_addr, NULL);
 	vsie_page->fault_addr = 0;
 }