-----Original Message----- From: kernelnewbies-bounces@xxxxxxxxxxxxxxxxx [mailto:kernelnewbies-bounces@xxxxxxxxxxxxxxxxx] On Behalf Of Arun KS Sent: Thursday, March 12, 2015 11:03 AM To: Sunny Shah Cc: kernelnewbies Subject: Re: Understanding the mapping of physical memory to kernel address space Hello Sunny, On Thu, Mar 12, 2015 at 10:32 PM, Sunny Shah <shahsunny715@xxxxxxxxx> wrote: > Hello, > > This is my first mail on this list, so please let me know if I'm erring. > > I'm reading Bovet and Cesati's "Understanding the Linux Kernel", > specifically the chapter "Memory Addressing", sub-section "Kernel Page > Tables". Here they describe how Linux initializes its page tables for > various RAM sizes and how much of the physical address space is mapped > onto the kernel virtual address space. > > I have several questions from my reading: > > My understanding is that the 32 bit virtual address space of a process > is split into 2 parts - the first 3 GiB for the user space and the > remaining 1GiB for the kernel (with the same kernel mapping being used > for all processes. However, although the kernel is mapped into the > higher portion of the address space, it resides in the lower 1 GiB of RAM. Is this correct? Yes. Incase of 3:1 mapping, kernel virtual address starts at 0xc0000000. You can also have 2:2 mappings aswell. It is a configurable option Just an FYI, I've seen 1:3 mapping too. We had to do that with the kernels we built when I was at one company because we needed 3GB of virtual address space to map all of the memory mapped registers on their ASICs. There's lots of options here. Jeff Haran _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
