Re: [Xen-devel] Question regarding swiotlb-xen in Linux kernel

[Joe Jin <joe.jin@xxxxxxxxxx>]

On 4/18/19 2:09 PM, Boris Ostrovsky wrote:
> On 4/18/19 3:36 AM, Juergen Gross wrote:
>> I'm currently investigating a problem related to swiotlb-xen. With a
>> specific driver a customer is capable to trigger a situation where a
>> MFN is mapped to multiple dom0 PFNs at the same time. There is no
>> guest involved, so this is not related to grants.
>>
>> Wit a debug kernel I have managed to track the inconsistency to a
>> call of xen_destroy_contiguous_region() from xen_swiotlb_free_coherent()
>> where the region was obviously not contiguous.
>>
>> xen_swiotlb_free_coherent() contains:
>>
>>         if (((dev_addr + size - 1 <= dma_mask)) ||
>>             range_straddles_page_boundary(phys, size))
>>                 xen_destroy_contiguous_region(phys, order);
>>
>> Shouldn't it be either:
>>
>>         if (((dev_addr + size - 1 <= dma_mask)) &&
>>             !range_straddles_page_boundary(phys, size))
>>                 xen_destroy_contiguous_region(phys, order);
> 
> +Joe
> 
> https://lists.xenproject.org/archives/html/xen-devel/2018-10/msg01920.html
> 
> (The discussion happened in
> https://lists.xenproject.org/archives/html/xen-devel/2018-10/msg01814.html)
> 
> And looks like we dropped it. Or was there a reason we haven't picked it up?

I remembered the concern was whether memory not from Xen.

Thanks,
Joe

> 
> 
> -boris
> 
> 
>>
>>
>> or:
>>
>>         if (dev_addr + size - 1 <= dma_mask) {
>>             BUG_ON(range_straddles_page_boundary(phys, size));
>>             xen_destroy_contiguous_region(phys, order);
>>         }
>>
>> as calling xen_destroy_contiguous_region() with a non-contiguous memory
>> region is a perfect receipt for a latent crash?
>>
>> The remaining question is why the driver is calling
>> xen_swiotlb_free_coherent() for a non-contiguous region, of course.
>>
>>
>> Juergen
> 


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