[PATCH] drm/ttm: Fix vma page_prot bit manipulation

[Jerome Glisse]

On Wed, Nov 06, 2013 at 09:41:03AM -0800, Thomas Hellstrom wrote:
> 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 at vmware.com>

Reviewed-by: Jerome Glisse <jglisse at redhat.com>

> ---
>  drivers/gpu/drm/ttm/ttm_bo_vm.c |   30 +++++++++++++-----------------
>  1 file changed, 13 insertions(+), 17 deletions(-)
> 
> diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c
> index c03514b..ac617f3 100644
> --- 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.
> -- 
> 1.7.10.4
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