Re: [PATCH V3 01/30] mm: Make vm_get_page_prot arch specific.

Paul Mackerras [off-list ref] writes:

On Thu, Feb 18, 2016 at 10:20:25PM +0530, Aneesh Kumar K.V wrote:

quoted

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.

This seems like unnecessary churn to me.  Let's just make hash use the
same values as radix for things like _PAGE_RW, _PAGE_EXEC etc., and
then we don't need any of this.

I was hoping to do that after this series. Something similar to

https://github.com/kvaneesh/linux/commit/0c2ac1328b678a6e187d1f2644a007204c59a047

"
powerpc/mm: Add helper for page flag access in ioremap_at

Instead of using variables we use static inline which get patched during
boot to either hash or radix version.
"

That gives us a base to revert patches if we find issues with hash and
still have a working radix base. So idea is to introduce radix with minimal
changes to hash and then consolidate hash and radix as much as we can by
updating hash linux format.

-aneesh