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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> 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Pretty outdated.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 




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