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

[Julien Grall <julien.grall@xxxxxxxxxx>]

On 06/11/2014 12:42, Stefano Stabellini wrote:
> On Thu, 6 Nov 2014, Julien Grall wrote:
> > 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.
> Yes, it is safe, but we do need to change those call sites to pass
> dev_addr instead, like I have done with unmap_single in the patch I
> appended in the last email:
Ok. I will give a look to modify all the call site.

Regards,

> 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
> @@ -449,7 +447,7 @@ static void xen_unmap_single(struct device *hwdev, 
> dma_addr_t dev_addr,
>
>         BUG_ON(dir == DMA_NONE);
>
> -       xen_dma_unmap_page(hwdev, paddr, size, dir, attrs);
> +       xen_dma_unmap_page(hwdev, dev_addr, size, dir, attrs);
>
>         /* NOTE: We use dev_addr here, not paddr! */
>         if (is_xen_swiotlb_buffer(dev_addr)) {
--
Julien Grall

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