<br><div> On x86 kernel is normally split into 3GB (user) : 1 GB (Kernel) spaces. Kernel can only directly </div><div> manipulate 1 GB (around 889 MB) from the PAGE_OFFSET (0xC0000000). The user space </div><div> memofy below PAGE_OFFSET kernel can't directly access, it considers this memory as </div>
<div> high memory. Kernel needs to kmap()/kmap_atomic() map user page and access that region.</div><div><br></div><div> If the memory is above 4 GB with page extension, it is clear that kernel can't access it as </div>
<div> kernel uses "void *" and/or "unsigned long" to hold the address. But it is not clear for me</div><div> why kernel's can't directly access memory below PAGE_OFFSET ( 0-3GB) directly.</div>
<div> </div><div><br></div><div>Regards</div><div><br></div><div>Kshemendra</div>