Re: [Xen-devel] kmap_atomic issue with SLES11SP1 32bit XEN driver code

[dbrace <dab@xxxxxx>]

Can you give me some URLs to documentation that can help me understand 
my issue?
Is sounds like I cannot go back to the correct virtual address after I 
map it for DMA.


On 12/15/2011 10:37 AM, Jan Beulich wrote:
> > > > On 15.12.11 at 17:15, "Brace, Don"<dab@xxxxxx>  wrote:
> > I do not understand what this means:
> > " That is, we'd be susceptible to this problem only if within a
> > lazy-mode enabled section k{,un}map_atomic were used
> > synchronously (which I'd consider a coding mistake)."
> >
> > Could you elaborate on this?
> Not sure what additional explanation is needed. kmap_atomic() is
> intended to be used in atomic context, and if you use it elsewhere
> that's a mis-use.
>
> > Here is what I am trying to do.
> > I am in a LLD I have bus addresses that are DMA-able that I would normally
> > DMA to except this driver is emulating hardware in software and so it does
> > not need to DMA is needs to transfer the data with the CPU.
> So this makes clear that what I told you about a possibly missing
> translation is likely the culprit. Quoting from your original mail
>
>                   linux_page = __pfn_to_page(physical_address>>  PAGE_SHIFT);
>
> I have to assume that physical_address really isn't a physical address,
> but a bus one. Hence you first need to translate it to a physical one
> before passing it to __pfn_to_page().
>
> > On non-XEN 32bit kernels I use kmap_atomic() and it handles both highmem
> > addresses and non highmem addresses with no issues.
> And so does it on Xen.
>
> > When I am running 32bit XEN kernels I run into issues like this:
> >      "BUG: unable to handle kernel paging request at 9822bf40"
> Because you pass in a random struct page *.
>
> Jan
--
Don Brace
SPSN Linux Development
Hewlett-Packard Company

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel