s390/mm: extended gmap pte notifier

The current gmap pte notifier forces a pte into to a read-write state.
If the pte is invalidated the gmap notifier is called to inform KVM
that the mapping will go away.

Extend this approach to allow read-write, read-only and no-access
as possible target states and call the pte notifier for any change
to the pte.

This mechanism is used to temporarily set specific access rights for
a pte without doing the heavy work of a true mprotect call.

Reviewed-by: David Hildenbrand <dahi@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>

2 files changed, 178 insertions, 46 deletions

diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
index 8b56423a8297..480c076afceb 100644
--- a/arch/s390/mm/gmap.c
+++ b/arch/s390/mm/gmap.c
@@ -553,29 +553,29 @@ static LIST_HEAD(gmap_notifier_list);
 static DEFINE_SPINLOCK(gmap_notifier_lock);
 
 /**
- * gmap_register_ipte_notifier - register a pte invalidation callback
+ * gmap_register_pte_notifier - register a pte invalidation callback
  * @nb: pointer to the gmap notifier block
  */
-void gmap_register_ipte_notifier(struct gmap_notifier *nb)
+void gmap_register_pte_notifier(struct gmap_notifier *nb)
 {
         spin_lock(&gmap_notifier_lock);
         list_add_rcu(&nb->list, &gmap_notifier_list);
         spin_unlock(&gmap_notifier_lock);
 }
-EXPORT_SYMBOL_GPL(gmap_register_ipte_notifier);
+EXPORT_SYMBOL_GPL(gmap_register_pte_notifier);
 
 /**
- * gmap_unregister_ipte_notifier - remove a pte invalidation callback
+ * gmap_unregister_pte_notifier - remove a pte invalidation callback
  * @nb: pointer to the gmap notifier block
  */
-void gmap_unregister_ipte_notifier(struct gmap_notifier *nb)
+void gmap_unregister_pte_notifier(struct gmap_notifier *nb)
 {
         spin_lock(&gmap_notifier_lock);
         list_del_rcu(&nb->list);
         spin_unlock(&gmap_notifier_lock);
         synchronize_rcu();
 }
-EXPORT_SYMBOL_GPL(gmap_unregister_ipte_notifier);
+EXPORT_SYMBOL_GPL(gmap_unregister_pte_notifier);
 
 /**
  * gmap_call_notifier - call all registered invalidation callbacks
@@ -593,62 +593,150 @@ static void gmap_call_notifier(struct gmap *gmap, unsigned long start,
 }
 
 /**
- * gmap_ipte_notify - mark a range of ptes for invalidation notification
+ * gmap_table_walk - walk the gmap page tables
+ * @gmap: pointer to guest mapping meta data structure
+ * @gaddr: virtual address in the guest address space
+ *
+ * Returns a table pointer for the given guest address.
+ */
+static inline unsigned long *gmap_table_walk(struct gmap *gmap,
+                                             unsigned long gaddr)
+{
+        unsigned long *table;
+
+        table = gmap->table;
+        switch (gmap->asce & _ASCE_TYPE_MASK) {
+        case _ASCE_TYPE_REGION1:
+                table += (gaddr >> 53) & 0x7ff;
+                if (*table & _REGION_ENTRY_INVALID)
+                        return NULL;
+                table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+                /* Fallthrough */
+        case _ASCE_TYPE_REGION2:
+                table += (gaddr >> 42) & 0x7ff;
+                if (*table & _REGION_ENTRY_INVALID)
+                        return NULL;
+                table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+                /* Fallthrough */
+        case _ASCE_TYPE_REGION3:
+                table += (gaddr >> 31) & 0x7ff;
+                if (*table & _REGION_ENTRY_INVALID)
+                        return NULL;
+                table = (unsigned long *)(*table & _REGION_ENTRY_ORIGIN);
+                /* Fallthrough */
+        case _ASCE_TYPE_SEGMENT:
+                table += (gaddr >> 20) & 0x7ff;
+        }
+        return table;
+}
+
+/**
+ * gmap_pte_op_walk - walk the gmap page table, get the page table lock
+ *                    and return the pte pointer
+ * @gmap: pointer to guest mapping meta data structure
+ * @gaddr: virtual address in the guest address space
+ * @ptl: pointer to the spinlock pointer
+ *
+ * Returns a pointer to the locked pte for a guest address, or NULL
+ */
+static pte_t *gmap_pte_op_walk(struct gmap *gmap, unsigned long gaddr,
+                               spinlock_t **ptl)
+{
+        unsigned long *table;
+
+        /* Walk the gmap page table, lock and get pte pointer */
+        table = gmap_table_walk(gmap, gaddr);
+        if (!table || *table & _SEGMENT_ENTRY_INVALID)
+                return NULL;
+        return pte_alloc_map_lock(gmap->mm, (pmd_t *) table, gaddr, ptl);
+}
+
+/**
+ * gmap_pte_op_fixup - force a page in and connect the gmap page table
+ * @gmap: pointer to guest mapping meta data structure
+ * @gaddr: virtual address in the guest address space
+ * @vmaddr: address in the host process address space
+ *
+ * Returns 0 if the caller can retry __gmap_translate (might fail again),
+ * -ENOMEM if out of memory and -EFAULT if anything goes wrong while fixing
+ * up or connecting the gmap page table.
+ */
+static int gmap_pte_op_fixup(struct gmap *gmap, unsigned long gaddr,
+                             unsigned long vmaddr)
+{
+        struct mm_struct *mm = gmap->mm;
+        bool unlocked = false;
+
+        if (fixup_user_fault(current, mm, vmaddr, FAULT_FLAG_WRITE, &unlocked))
+                return -EFAULT;
+        if (unlocked)
+                /* lost mmap_sem, caller has to retry __gmap_translate */
+                return 0;
+        /* Connect the page tables */
+        return __gmap_link(gmap, gaddr, vmaddr);
+}
+
+/**
+ * gmap_pte_op_end - release the page table lock
+ * @ptl: pointer to the spinlock pointer
+ */
+static void gmap_pte_op_end(spinlock_t *ptl)
+{
+        spin_unlock(ptl);
+}
+
+/**
+ * gmap_mprotect_notify - change access rights for a range of ptes and
+ *                        call the notifier if any pte changes again
  * @gmap: pointer to guest mapping meta data structure
  * @gaddr: virtual address in the guest address space
  * @len: size of area
+ * @prot: indicates access rights: PROT_NONE, PROT_READ or PROT_WRITE
  *
- * Returns 0 if for each page in the given range a gmap mapping exists and
- * the invalidation notification could be set. If the gmap mapping is missing
- * for one or more pages -EFAULT is returned. If no memory could be allocated
- * -ENOMEM is returned. This function establishes missing page table entries.
+ * Returns 0 if for each page in the given range a gmap mapping exists,
+ * the new access rights could be set and the notifier could be armed.
+ * If the gmap mapping is missing for one or more pages -EFAULT is
+ * returned. If no memory could be allocated -ENOMEM is returned.
+ * This function establishes missing page table entries.
  */
-int gmap_ipte_notify(struct gmap *gmap, unsigned long gaddr, unsigned long len)
+int gmap_mprotect_notify(struct gmap *gmap, unsigned long gaddr,
+                         unsigned long len, int prot)
 {
-        unsigned long addr;
+        unsigned long vmaddr;
         spinlock_t *ptl;
         pte_t *ptep;
-        bool unlocked;
         int rc = 0;
 
         if ((gaddr & ~PAGE_MASK) || (len & ~PAGE_MASK))
                 return -EINVAL;
+        if (!MACHINE_HAS_ESOP && prot == PROT_READ)
+                return -EINVAL;
         down_read(&gmap->mm->mmap_sem);
         while (len) {
-                unlocked = false;
-                /* Convert gmap address and connect the page tables */
-                addr = __gmap_translate(gmap, gaddr);
-                if (IS_ERR_VALUE(addr)) {
-                        rc = addr;
-                        break;
-                }
-                /* Get the page mapped */
-                if (fixup_user_fault(current, gmap->mm, addr, FAULT_FLAG_WRITE,
-                                     &unlocked)) {
-                        rc = -EFAULT;
-                        break;
+                rc = -EAGAIN;
+                ptep = gmap_pte_op_walk(gmap, gaddr, &ptl);
+                if (ptep) {
+                        rc = ptep_force_prot(gmap->mm, gaddr, ptep, prot);
+                        gmap_pte_op_end(ptl);
                 }
-                /* While trying to map mmap_sem got unlocked. Let us retry */
-                if (unlocked)
+                if (rc) {
+                        vmaddr = __gmap_translate(gmap, gaddr);
+                        if (IS_ERR_VALUE(vmaddr)) {
+                                rc = vmaddr;
+                                break;
+                        }
+                        rc = gmap_pte_op_fixup(gmap, gaddr, vmaddr);
+                        if (rc)
+                                break;
                         continue;
-                rc = __gmap_link(gmap, gaddr, addr);
-                if (rc)
-                        break;
-                /* Walk the process page table, lock and get pte pointer */
-                ptep = get_locked_pte(gmap->mm, addr, &ptl);
-                VM_BUG_ON(!ptep);
-                /* Set notification bit in the pgste of the pte */
-                if ((pte_val(*ptep) & (_PAGE_INVALID | _PAGE_PROTECT)) == 0) {
-                        ptep_set_notify(gmap->mm, addr, ptep);
-                        gaddr += PAGE_SIZE;
-                        len -= PAGE_SIZE;
                 }
-                pte_unmap_unlock(ptep, ptl);
+                gaddr += PAGE_SIZE;
+                len -= PAGE_SIZE;
         }
         up_read(&gmap->mm->mmap_sem);
         return rc;
 }
-EXPORT_SYMBOL_GPL(gmap_ipte_notify);
+EXPORT_SYMBOL_GPL(gmap_mprotect_notify);
 
 /**
  * ptep_notify - call all invalidation callbacks for a specific pte.
diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
index fa286d0c0f2d..ab65fb11e058 100644
--- a/arch/s390/mm/pgtable.c
+++ b/arch/s390/mm/pgtable.c
@@ -179,9 +179,9 @@ static inline pgste_t pgste_set_pte(pte_t *ptep, pgste_t pgste, pte_t entry)
         return pgste;
 }
 
-static inline pgste_t pgste_ipte_notify(struct mm_struct *mm,
-                                        unsigned long addr,
-                                        pte_t *ptep, pgste_t pgste)
+static inline pgste_t pgste_pte_notify(struct mm_struct *mm,
+                                       unsigned long addr,
+                                       pte_t *ptep, pgste_t pgste)
 {
 #ifdef CONFIG_PGSTE
         if (pgste_val(pgste) & PGSTE_IN_BIT) {
@@ -199,7 +199,7 @@ static inline pgste_t ptep_xchg_start(struct mm_struct *mm,
 
         if (mm_has_pgste(mm)) {
                 pgste = pgste_get_lock(ptep);
-                pgste = pgste_ipte_notify(mm, addr, ptep, pgste);
+                pgste = pgste_pte_notify(mm, addr, ptep, pgste);
         }
         return pgste;
 }
@@ -414,6 +414,50 @@ void ptep_set_notify(struct mm_struct *mm, unsigned long addr, pte_t *ptep)
         pgste_set_unlock(ptep, pgste);
 }
 
+/**
+ * ptep_force_prot - change access rights of a locked pte
+ * @mm: pointer to the process mm_struct
+ * @addr: virtual address in the guest address space
+ * @ptep: pointer to the page table entry
+ * @prot: indicates guest access rights: PROT_NONE, PROT_READ or PROT_WRITE
+ *
+ * Returns 0 if the access rights were changed and -EAGAIN if the current
+ * and requested access rights are incompatible.
+ */
+int ptep_force_prot(struct mm_struct *mm, unsigned long addr,
+                    pte_t *ptep, int prot)
+{
+        pte_t entry;
+        pgste_t pgste;
+        int pte_i, pte_p;
+
+        pgste = pgste_get_lock(ptep);
+        entry = *ptep;
+        /* Check pte entry after all locks have been acquired */
+        pte_i = pte_val(entry) & _PAGE_INVALID;
+        pte_p = pte_val(entry) & _PAGE_PROTECT;
+        if ((pte_i && (prot != PROT_NONE)) ||
+            (pte_p && (prot & PROT_WRITE))) {
+                pgste_set_unlock(ptep, pgste);
+                return -EAGAIN;
+        }
+        /* Change access rights and set the pgste notification bit */
+        if (prot == PROT_NONE && !pte_i) {
+                ptep_flush_direct(mm, addr, ptep);
+                pgste = pgste_update_all(entry, pgste, mm);
+                pte_val(entry) |= _PAGE_INVALID;
+        }
+        if (prot == PROT_READ && !pte_p) {
+                ptep_flush_direct(mm, addr, ptep);
+                pte_val(entry) &= ~_PAGE_INVALID;
+                pte_val(entry) |= _PAGE_PROTECT;
+        }
+        pgste_val(pgste) |= PGSTE_IN_BIT;
+        pgste = pgste_set_pte(ptep, pgste, entry);
+        pgste_set_unlock(ptep, pgste);
+        return 0;
+}
+
 static void ptep_zap_swap_entry(struct mm_struct *mm, swp_entry_t entry)
 {
         if (!non_swap_entry(entry))
@@ -483,7 +527,7 @@ bool test_and_clear_guest_dirty(struct mm_struct *mm, unsigned long addr)
         pgste_val(pgste) &= ~PGSTE_UC_BIT;
         pte = *ptep;
         if (dirty && (pte_val(pte) & _PAGE_PRESENT)) {
-                pgste = pgste_ipte_notify(mm, addr, ptep, pgste);
+                pgste = pgste_pte_notify(mm, addr, ptep, pgste);
                 __ptep_ipte(addr, ptep);
                 if (MACHINE_HAS_ESOP || !(pte_val(pte) & _PAGE_WRITE))
                         pte_val(pte) |= _PAGE_PROTECT;