Re: xen/arm: kernel BUG at /local/home/julien/works/linux/drivers/xen/swiotlb-xen.c:102

[Julien Grall <julien.grall@linaro.org>]

On 06/11/2014 11:46, Stefano Stabellini wrote:
> Hello Julien,

Hi Stefano,

> I didn't manage to reproduce the issue you are seeing but I think you
> are right: non-LPAE kernels could get in trouble by calling
> xen_bus_to_phys. This problem is not ARM specific per se, but it doesn't
> occur on x86 because config XEN depends on X86_32 && X86_PAE.
>
> The following patch should fix the issue:
>
>
> diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c
> index ac5d41b..489620d 100644
> --- a/drivers/xen/swiotlb-xen.c
> +++ b/drivers/xen/swiotlb-xen.c
> @@ -96,8 +96,6 @@ static inline phys_addr_t xen_bus_to_phys(dma_addr_t baddr)
>   	dma_addr_t dma = (dma_addr_t)pfn << PAGE_SHIFT;
>   	phys_addr_t paddr = dma;
>
> -	BUG_ON(paddr != dma); /* truncation has occurred, should never happen */
> -

Are you sure that removing this BUG_ON is safe? There is some of place 
where we pass a physical address rather than a DMA. See 
xen_swiotlb_sync_single.

Regards,

-- 
Julien Grall