dax: Implement dax_finish_sync_fault()

Implement a function that filesystems can call to finish handling of
synchronous page faults. It takes care of syncing appropriare file range
and insertion of page table entry.

Reviewed-by: Ross Zwisler <ross.zwisler@linux.intel.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>

1 files changed, 83 insertions, 0 deletions

diff --git a/fs/dax.c b/fs/dax.c
index bb9ff907738c..78233c716757 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1492,3 +1492,86 @@ int dax_iomap_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
         }
 }
 EXPORT_SYMBOL_GPL(dax_iomap_fault);
+
+/**
+ * dax_insert_pfn_mkwrite - insert PTE or PMD entry into page tables
+ * @vmf: The description of the fault
+ * @pe_size: Size of entry to be inserted
+ * @pfn: PFN to insert
+ *
+ * This function inserts writeable PTE or PMD entry into page tables for mmaped
+ * DAX file.  It takes care of marking corresponding radix tree entry as dirty
+ * as well.
+ */
+static int dax_insert_pfn_mkwrite(struct vm_fault *vmf,
+                                  enum page_entry_size pe_size,
+                                  pfn_t pfn)
+{
+        struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+        void *entry, **slot;
+        pgoff_t index = vmf->pgoff;
+        int vmf_ret, error;
+
+        spin_lock_irq(&mapping->tree_lock);
+        entry = get_unlocked_mapping_entry(mapping, index, &slot);
+        /* Did we race with someone splitting entry or so? */
+        if (!entry ||
+            (pe_size == PE_SIZE_PTE && !dax_is_pte_entry(entry)) ||
+            (pe_size == PE_SIZE_PMD && !dax_is_pmd_entry(entry))) {
+                put_unlocked_mapping_entry(mapping, index, entry);
+                spin_unlock_irq(&mapping->tree_lock);
+                trace_dax_insert_pfn_mkwrite_no_entry(mapping->host, vmf,
+                                                      VM_FAULT_NOPAGE);
+                return VM_FAULT_NOPAGE;
+        }
+        radix_tree_tag_set(&mapping->page_tree, index, PAGECACHE_TAG_DIRTY);
+        entry = lock_slot(mapping, slot);
+        spin_unlock_irq(&mapping->tree_lock);
+        switch (pe_size) {
+        case PE_SIZE_PTE:
+                error = vm_insert_mixed_mkwrite(vmf->vma, vmf->address, pfn);
+                vmf_ret = dax_fault_return(error);
+                break;
+#ifdef CONFIG_FS_DAX_PMD
+        case PE_SIZE_PMD:
+                vmf_ret = vmf_insert_pfn_pmd(vmf->vma, vmf->address, vmf->pmd,
+                        pfn, true);
+                break;
+#endif
+        default:
+                vmf_ret = VM_FAULT_FALLBACK;
+        }
+        put_locked_mapping_entry(mapping, index);
+        trace_dax_insert_pfn_mkwrite(mapping->host, vmf, vmf_ret);
+        return vmf_ret;
+}
+
+/**
+ * dax_finish_sync_fault - finish synchronous page fault
+ * @vmf: The description of the fault
+ * @pe_size: Size of entry to be inserted
+ * @pfn: PFN to insert
+ *
+ * This function ensures that the file range touched by the page fault is
+ * stored persistently on the media and handles inserting of appropriate page
+ * table entry.
+ */
+int dax_finish_sync_fault(struct vm_fault *vmf, enum page_entry_size pe_size,
+                          pfn_t pfn)
+{
+        int err;
+        loff_t start = ((loff_t)vmf->pgoff) << PAGE_SHIFT;
+        size_t len = 0;
+
+        if (pe_size == PE_SIZE_PTE)
+                len = PAGE_SIZE;
+        else if (pe_size == PE_SIZE_PMD)
+                len = PMD_SIZE;
+        else
+                WARN_ON_ONCE(1);
+        err = vfs_fsync_range(vmf->vma->vm_file, start, start + len - 1, 1);
+        if (err)
+                return VM_FAULT_SIGBUS;
+        return dax_insert_pfn_mkwrite(vmf, pe_size, pfn);
+}
+EXPORT_SYMBOL_GPL(dax_finish_sync_fault);