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

[dbrace <dab@xxxxxx>]

> > ... without knowing where you got physical_address from it's impossible
> > to tell whether your problem is that under Xen physical and machine
> > (sometimes called "bus") addresses being distinct (end hence you're
??possibly lacking a translation between the two).


Is there a way to tell from the address is this is happening?

On 12/12/2011 09:16 AM, Jan Beulich wrote:
> > > > On 07.12.11 at 22:47, dbrace<dab@xxxxxx>  wrote:
> > kernel: Linux 360 2.6.32.12-0.7-xen #1 SMP 2010-05-20 11:14:20 +0200
> > i686 i686 i386 GNU/Linux
> Pretty outdated.
>
> > I am having issues with some code that uses kmap_atomic(). I am getting:
> >
> > BUG: unable to handle kernel paging request at 23a1a000 (which is the
> > address returned from kmap_atomic().)
> For a valid high memory page this is surely not being returned by
> kmap_atomic(), so we have to assume that what you started with is
> the address of a low memory one.
>
> > The same code works when running on non-XEN 32bit kernels so I am
> > wondering why this does not work under
> > XEN kernels. Is there a different approach that I need to take for 32bit
> > XEN kernels?
> No, but ...
>
> > I really only need to do this code segment if the memory address is a
> > high memory address. Is there a MACRO or function
> > that can help me determine this?
> PageHighMem().
>
> > Here is a code snippet:
> >
> >                   void *linux_vaddr = NULL;       /* kmapped temporary
> > virtual address */
> >                   int linux_page_offset = 0;      /* offset in page */
> >                   int count = 0;                  /* bytes left to
> > transfer */
> >                   int left = byte_count;          /* number of bytes left
> > to transfer */
> >                   int memcpysize = 0;             /* current size to
> > transfer */
> >                   struct page *linux_page = NULL; /* calculated page */
> >                   int kmap_flags = 0;
> >
> >                   linux_page = __pfn_to_page(physical_address>>  PAGE_SHIFT);
> ... without knowing where you got physical_address from it's impossible
> to tell whether your problem is that under Xen physical and machine
> (sometimes called "bus") addresses being distinct (end hence you're
> possibly lacking a translation between the two).
>
> Jan
>
> >                   linux_page_offset = (physical_address&
> > 0x0000000000000FFFULL);
> >                   memcpysize =  min((PAGE_SIZE - linux_page_offset), left);
> >
> >                   kmap_flags = KM_USER0;
> >
> >                   linux_vaddr = kmap_atomic(linux_page, kmap_flags) +
> > linux_page_offset;
> >
> >                   printk("%s: called kmap_atomic, "
> >                           "calling memcpy linux_vaddr = 0x%x virt_address
> > = 0x%x count = 0x%x\n",
> >                           __func__, linux_vaddr, virt_address, count);
> >                   /*
> >                    * Either need to copy to a kmapped destination
> >                    * or a kmapped source.
> >                    */
> >                   if (type == 0) // Write to s/g element, dest virtual
> > addr was known.
> >                           memcpy((void *)virt_address+count, (void
> > *)linux_vaddr, memcpysize);
> >                   else // Source virt. address was known.
> >                           memcpy((void *)linux_vaddr, (void
> > *)virt_address+count, memcpysize);
> >
> >                   printk("OS_Linux32_Xfer_SG_Page: calling kunmap_atomic, "
> >                           "calling memcpy linux_vaddr = 0x%lx\n",
> > linux_vaddr);
> >
> >                   kunmap_atomic(linux_vaddr, kmap_flags);
> >
> >
> > --
> > Don Brace
> > SPSN Linux Development
> > Hewlett-Packard Company
> >
> > _______________________________________________
> > Xen-devel mailing list
> > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > http://lists.xensource.com/xen-devel
--
Don Brace
SPSN Linux Development
Hewlett-Packard Company

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