KVM: s390: remove the last user of page->index

Shadow page tables use page->index to keep the g2 address of the guest
page table being shadowed.

Instead of keeping the information in page->index, split the address
and smear it over the 16-bit softbits areas of 4 PGSTEs.

This removes the last s390 user of page->index.

Reviewed-by: Steffen Eiden <seiden@linux.ibm.com>
Reviewed-by: Christoph Schlameuss <schlameuss@linux.ibm.com>
Link: https://lore.kernel.org/r/20250123144627.312456-16-imbrenda@linux.ibm.com
Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
Message-ID: <20250123144627.312456-16-imbrenda@linux.ibm.com>

Author: Claudio Imbrenda

arch/s390/include/asm/pgtable.h

@@ -420,6 +420,7 @@ void setup_protection_map(void);
 #define PGSTE_HC_BIT	0x0020000000000000UL
 #define PGSTE_GR_BIT	0x0004000000000000UL
 #define PGSTE_GC_BIT	0x0002000000000000UL
+#define PGSTE_ST2_MASK	0x0000ffff00000000UL
 #define PGSTE_UC_BIT	0x0000000000008000UL	/* user dirty (migration) */
 #define PGSTE_IN_BIT	0x0000000000004000UL	/* IPTE notify bit */
 #define PGSTE_VSIE_BIT	0x0000000000002000UL	/* ref'd in a shadow table */
@@ -2007,4 +2008,18 @@ extern void s390_reset_cmma(struct mm_struct *mm);
 #define pmd_pgtable(pmd) \
 	((pgtable_t)__va(pmd_val(pmd) & -sizeof(pte_t)*PTRS_PER_PTE))
 
+static inline unsigned long gmap_pgste_get_pgt_addr(unsigned long *pgt)
+{
+	unsigned long *pgstes, res;
+
+	pgstes = pgt + _PAGE_ENTRIES;
+
+	res = (pgstes[0] & PGSTE_ST2_MASK) << 16;
+	res |= pgstes[1] & PGSTE_ST2_MASK;
+	res |= (pgstes[2] & PGSTE_ST2_MASK) >> 16;
+	res |= (pgstes[3] & PGSTE_ST2_MASK) >> 32;
+
+	return res;
+}
+
 #endif /* _S390_PAGE_H */

arch/s390/kvm/gaccess.c

@@ -1409,6 +1409,7 @@ static int kvm_s390_shadow_tables(struct gmap *sg, unsigned long saddr,
 static int shadow_pgt_lookup(struct gmap *sg, unsigned long saddr, unsigned long *pgt,
 			     int *dat_protection, int *fake)
 {
+	unsigned long pt_index;
 	unsigned long *table;
 	struct page *page;
 	int rc;
@@ -1418,9 +1419,10 @@ static int shadow_pgt_lookup(struct gmap *sg, unsigned long saddr, unsigned long
 	if (table && !(*table & _SEGMENT_ENTRY_INVALID)) {
 		/* Shadow page tables are full pages (pte+pgste) */
 		page = pfn_to_page(*table >> PAGE_SHIFT);
-		*pgt = page->index & ~GMAP_SHADOW_FAKE_TABLE;
+		pt_index = gmap_pgste_get_pgt_addr(page_to_virt(page));
+		*pgt = pt_index & ~GMAP_SHADOW_FAKE_TABLE;
 		*dat_protection = !!(*table & _SEGMENT_ENTRY_PROTECT);
-		*fake = !!(page->index & GMAP_SHADOW_FAKE_TABLE);
+		*fake = !!(pt_index & GMAP_SHADOW_FAKE_TABLE);
 		rc = 0;
 	} else  {
 		rc = -EAGAIN;

arch/s390/mm/gmap.c

@@ -1733,6 +1733,23 @@ int gmap_shadow_sgt(struct gmap *sg, unsigned long saddr, unsigned long sgt,
 }
 EXPORT_SYMBOL_GPL(gmap_shadow_sgt);
 
+static void gmap_pgste_set_pgt_addr(struct ptdesc *ptdesc, unsigned long pgt_addr)
+{
+	unsigned long *pgstes = page_to_virt(ptdesc_page(ptdesc));
+
+	pgstes += _PAGE_ENTRIES;
+
+	pgstes[0] &= ~PGSTE_ST2_MASK;
+	pgstes[1] &= ~PGSTE_ST2_MASK;
+	pgstes[2] &= ~PGSTE_ST2_MASK;
+	pgstes[3] &= ~PGSTE_ST2_MASK;
+
+	pgstes[0] |= (pgt_addr >> 16) & PGSTE_ST2_MASK;
+	pgstes[1] |= pgt_addr & PGSTE_ST2_MASK;
+	pgstes[2] |= (pgt_addr << 16) & PGSTE_ST2_MASK;
+	pgstes[3] |= (pgt_addr << 32) & PGSTE_ST2_MASK;
+}
+
 /**
  * gmap_shadow_pgt - instantiate a shadow page table
  * @sg: pointer to the shadow guest address space structure
@@ -1760,9 +1777,10 @@ int gmap_shadow_pgt(struct gmap *sg, unsigned long saddr, unsigned long pgt,
 	ptdesc = page_table_alloc_pgste(sg->mm);
 	if (!ptdesc)
 		return -ENOMEM;
-	ptdesc->pt_index = pgt & _SEGMENT_ENTRY_ORIGIN;
+	origin = pgt & _SEGMENT_ENTRY_ORIGIN;
 	if (fake)
-		ptdesc->pt_index |= GMAP_SHADOW_FAKE_TABLE;
+		origin |= GMAP_SHADOW_FAKE_TABLE;
+	gmap_pgste_set_pgt_addr(ptdesc, origin);
 	s_pgt = page_to_phys(ptdesc_page(ptdesc));
 	/* Install shadow page table */
 	spin_lock(&sg->guest_table_lock);