Merge tag 'powerpc-4.17-1' of git://git.kernel.org/pub/scm/linux/kernel/git/powerpc/linux

[linux.git] / drivers / misc / cxl / cxllib.c

diff --git a/drivers/misc/cxl/cxllib.c b/drivers/misc/cxl/cxllib.c
index bea1eb004b493eb7073143ce61aaecdf0b83238f..0bc7c31cf7395734a1053f7cc10840c970b3eda9 100644 (file)
--- a/drivers/misc/cxl/cxllib.c
+++ b/drivers/misc/cxl/cxllib.c
@@ -208,49 +208,74 @@ int cxllib_get_PE_attributes(struct task_struct *task,
 }
 EXPORT_SYMBOL_GPL(cxllib_get_PE_attributes);
 
-int cxllib_handle_fault(struct mm_struct *mm, u64 addr, u64 size, u64 flags)
+static int get_vma_info(struct mm_struct *mm, u64 addr,
+                       u64 *vma_start, u64 *vma_end,
+                       unsigned long *page_size)
 {
-       int rc;
-       u64 dar;
        struct vm_area_struct *vma = NULL;
-       unsigned long page_size;
-
-       if (mm == NULL)
-               return -EFAULT;
+       int rc = 0;
 
        down_read(&mm->mmap_sem);
 
        vma = find_vma(mm, addr);
        if (!vma) {
-               pr_err("Can't find vma for addr %016llx\n", addr);
                rc = -EFAULT;
                goto out;
        }
-       /* get the size of the pages allocated */
-       page_size = vma_kernel_pagesize(vma);
-
-       for (dar = (addr & ~(page_size - 1)); dar < (addr + size); dar += page_size) {
-               if (dar < vma->vm_start || dar >= vma->vm_end) {
-                       vma = find_vma(mm, addr);
-                       if (!vma) {
-                               pr_err("Can't find vma for addr %016llx\n", addr);
-                               rc = -EFAULT;
-                               goto out;
-                       }
-                       /* get the size of the pages allocated */
-                       page_size = vma_kernel_pagesize(vma);
+       *page_size = vma_kernel_pagesize(vma);
+       *vma_start = vma->vm_start;
+       *vma_end = vma->vm_end;
+out:
+       up_read(&mm->mmap_sem);
+       return rc;
+}
+
+int cxllib_handle_fault(struct mm_struct *mm, u64 addr, u64 size, u64 flags)
+{
+       int rc;
+       u64 dar, vma_start, vma_end;
+       unsigned long page_size;
+
+       if (mm == NULL)
+               return -EFAULT;
+
+       /*
+        * The buffer we have to process can extend over several pages
+        * and may also cover several VMAs.
+        * We iterate over all the pages. The page size could vary
+        * between VMAs.
+        */
+       rc = get_vma_info(mm, addr, &vma_start, &vma_end, &page_size);
+       if (rc)
+               return rc;
+
+       for (dar = (addr & ~(page_size - 1)); dar < (addr + size);
+            dar += page_size) {
+               if (dar < vma_start || dar >= vma_end) {
+                       /*
+                        * We don't hold the mm->mmap_sem semaphore
+                        * while iterating, since the semaphore is
+                        * required by one of the lower-level page
+                        * fault processing functions and it could
+                        * create a deadlock.
+                        *
+                        * It means the VMAs can be altered between 2
+                        * loop iterations and we could theoretically
+                        * miss a page (however unlikely). But that's
+                        * not really a problem, as the driver will
+                        * retry access, get another page fault on the
+                        * missing page and call us again.
+                        */
+                       rc = get_vma_info(mm, dar, &vma_start, &vma_end,
+                                       &page_size);
+                       if (rc)
+                               return rc;
                }
 
                rc = cxl_handle_mm_fault(mm, flags, dar);
-               if (rc) {
-                       pr_err("cxl_handle_mm_fault failed %d", rc);
-                       rc = -EFAULT;
-                       goto out;
-               }
+               if (rc)
+                       return -EFAULT;
        }
-       rc = 0;
-out:
-       up_read(&mm->mmap_sem);
-       return rc;
+       return 0;
 }
 EXPORT_SYMBOL_GPL(cxllib_handle_fault);