Re: Problem with MMAP on Xen kernel

[David Vrabel <david.vrabel@citrix.com>]

On 16/01/15 18:24, Dugger, Donald D wrote:
> One of our engineers, Maciek, is working on a driver and stumbled upon
> what looks like a bug in the Xen kernel.  The report I got was:
> 
>  
> 
> We recently started to provide mmap functionality in our driver for
> Linux. Function for this:
> 
>  
> 
> /int/
> 
> /NalMmap(/
> 
> /    struct file*                            File,/
> 
> /    struct vm_area_struct*  Vma/
> 
> /    )/
> 
> /{/
> 
> /    if(remap_pfn_range(Vma,/
> 
> /        Vma->vm_start,/
> 
> /        Vma->vm_pgoff,/
> 
> /        Vma->vm_end - Vma->vm_start,/
> 
> /        Vma->vm_page_prot))/
> 
> /    {/
> 
> /        return -EAGAIN;/
> 
> /    }/
> 
> / /
> 
> /    return 0;/
> 
> /}/
> 
>  
> 
> We discovered that this doesn’t work for xen kernels (but it doesn’t
> return any error, just does not map). I found that it is suggested to
> use io_remap_pfn_range instead of remap_pfn_range. After switching
> function everything still works on standard kernel, but on xen this time
> it returns error.

Not a lot to go on here.  What kernel version?  What PFNs are you trying
to map (RAM? MMIO?)  What error do you get?

Can you provide a minimal driver that shows the problem?

David