[PATCH V2 07/29] mm: Make vm_get_page_prot arch specific.

[Paul Mackerras]

On Mon, Feb 08, 2016 at 02:50:19PM +0530, Aneesh Kumar K.V wrote:
> With next generation power processor, we are having a new mmu model
> [1] that require us to maintain a different linux page table format.
> 
> Inorder to support both current and future ppc64 systems with a single
> kernel we need to make sure kernel can select between different page
> table format at runtime. With the new MMU (radix MMU) added, we will
> have to dynamically switch between different protection map. Hence
> override vm_get_page_prot instead of using arch_vm_get_page_prot. We
> also drop arch_vm_get_page_prot since only powerpc used it.

What's different about ISA v3.0 that means that the protection_map[]
entries need to be different?

If it's just different bit assignments for things like _PAGE_READ
etc., couldn't we fix this up at early boot time by writing new values
into protection_map[]?  Is there a reason why that wouldn't work, or
why you don't want to do that?

Paul.