DMA using data buffer vmapped in kernel space

[thomas@koeller.dyndns.org (Thomas Koeller)]

Am Donnerstag, 4. M?rz 2010 22:36:34 schrieb Russell King - ARM Linux:
> Cache maintainence is done using virtual addresses for L1, and
> physical addresses for L2.  There's the need for virtual addresses
> to be translatable to physical addresses, which is only true for
> the kernel direct mapped region (pages between PAGE_OFFSET and
> high_memory).

Isn't the mapping created by vmap() sufficient for the virt/phys
translation? In which way is this case different from a buffer
passed in from user space, where the constituent pages are not
in the directly mapped kernel region either?

tk