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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

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:


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)) {

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