drm/ttm: Fix vma page_prot bit manipulation

Fix a long-standing TTM issue where we manipulated the vma page_prot
bits while mmap_sem was taken in read mode only. We now make a local
copy of the vma structure which we pass when we set the ptes.

Signed-off-by: Thomas Hellstrom <thellstrom@vmware.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>

diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
index c03514b..ac617f3 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_bo_vm.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c
@@ -102,6 +102,7 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
        int retval = VM_FAULT_NOPAGE;
        struct ttm_mem_type_manager *man =
                &bdev->man[bo->mem.mem_type];
+       struct vm_area_struct cvma;
 
        /*
         * Work around locking order reversal in fault / nopfn
@@ -164,26 +165,21 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
        }
 
        /*
-        * Strictly, we're not allowed to modify vma->vm_page_prot here,
-        * since the mmap_sem is only held in read mode. However, we
-        * modify only the caching bits of vma->vm_page_prot and
-        * consider those bits protected by
-        * the bo->mutex, as we should be the only writers.
-        * There shouldn't really be any readers of these bits except
-        * within vm_insert_mixed()? fork?
-        *
-        * TODO: Add a list of vmas to the bo, and change the
-        * vma->vm_page_prot when the object changes caching policy, with
-        * the correct locks held.
+        * Make a local vma copy to modify the page_prot member
+        * and vm_flags if necessary. The vma parameter is protected
+        * by mmap_sem in write mode.
         */
+       cvma = *vma;
+       cvma.vm_page_prot = vm_get_page_prot(cvma.vm_flags);
+
        if (bo->mem.bus.is_iomem) {
-               vma->vm_page_prot = ttm_io_prot(bo->mem.placement,
-                                               vma->vm_page_prot);
+               cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
+                                               cvma.vm_page_prot);
        } else {
                ttm = bo->ttm;
-               vma->vm_page_prot = (bo->mem.placement & TTM_PL_FLAG_CACHED) ?
-                   vm_get_page_prot(vma->vm_flags) :
-                   ttm_io_prot(bo->mem.placement, vma->vm_page_prot);
+               if (!(bo->mem.placement & TTM_PL_FLAG_CACHED))
+                       cvma.vm_page_prot = ttm_io_prot(bo->mem.placement,
+                                                       cvma.vm_page_prot);
 
                /* Allocate all page at once, most common usage */
                if (ttm->bdev->driver->ttm_tt_populate(ttm)) {
@@ -210,7 +206,7 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
                        pfn = page_to_pfn(page);
                }
 
-               ret = vm_insert_mixed(vma, address, pfn);
+               ret = vm_insert_mixed(&cvma, address, pfn);
                /*
                 * Somebody beat us to this PTE or prefaulting to
                 * an already populated PTE, or prefaulting error.