Re: [PATCH] openrisc: Fix pagewalk usage in arch_dma_{clear,set}_uncached

[Stafford Horne <shorne@gmail.com>]

On Thu, Oct 06, 2022 at 08:33:01PM +0200, Jann Horn wrote:
> Since commit 8782fb61cc848 ("mm: pagewalk: Fix race between unmap and page
> walker"), walk_page_range() on kernel ranges won't work anymore,
> walk_page_range_novma() must be used instead.
> 
> Note: I don't have an openrisc development setup, so this is completely
> untested.
> 
> Fixes: 8782fb61cc848 ("mm: pagewalk: Fix race between unmap and page walker")
> Signed-off-by: Jann Horn <jannh@google.com>

This looks good to me, I will queue it for 6.1 fixes.

> ---
> Normally I would CC stable on a patch like this, but openrisc is mostly an
> in-development thing, so fixing stable kernels doesn't matter much, I assume?

In general we try to keep stable releases stable buy backporting OpenRISC patches
as well.  Just having the 'Fixes' tag should trigger to get this patched
backported to stable.  We should at least cc the LKML though.

-Stafford

>  arch/openrisc/kernel/dma.c | 16 ++++++++--------
>  1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/openrisc/kernel/dma.c b/arch/openrisc/kernel/dma.c
> index a82b2caaa560d..b3edbb33b621d 100644
> --- a/arch/openrisc/kernel/dma.c
> +++ b/arch/openrisc/kernel/dma.c
> @@ -74,10 +74,10 @@ void *arch_dma_set_uncached(void *cpu_addr, size_t size)
>  	 * We need to iterate through the pages, clearing the dcache for
>  	 * them and setting the cache-inhibit bit.
>  	 */
> -	mmap_read_lock(&init_mm);
> -	error = walk_page_range(&init_mm, va, va + size, &set_nocache_walk_ops,
> -			NULL);
> -	mmap_read_unlock(&init_mm);
> +	mmap_write_lock(&init_mm);
> +	error = walk_page_range_novma(&init_mm, va, va + size,
> +			&set_nocache_walk_ops, NULL, NULL);
> +	mmap_write_unlock(&init_mm);
>  
>  	if (error)
>  		return ERR_PTR(error);
> @@ -88,11 +88,11 @@ void arch_dma_clear_uncached(void *cpu_addr, size_t size)
>  {
>  	unsigned long va = (unsigned long)cpu_addr;
>  
> -	mmap_read_lock(&init_mm);
> +	mmap_write_lock(&init_mm);
>  	/* walk_page_range shouldn't be able to fail here */
> -	WARN_ON(walk_page_range(&init_mm, va, va + size,
> -			&clear_nocache_walk_ops, NULL));
> -	mmap_read_unlock(&init_mm);
> +	WARN_ON(walk_page_range_novma(&init_mm, va, va + size,
> +			&clear_nocache_walk_ops, NULL, NULL));
> +	mmap_write_unlock(&init_mm);
>  }
>  
>  void arch_sync_dma_for_device(phys_addr_t addr, size_t size,
> 
> base-commit: 7e6739b9336e61fe23ca4e2c8d1fda8f19f979bf
> -- 
> 2.38.0.rc1.362.ged0d419d3c-goog
>