[RFC PATCH V4 1/6] riscv: pgtable: Add custom protection_map init

[Christoph Hellwig]

On Sat, Sep 11, 2021 at 05:21:34PM +0800, guoren at kernel.org wrote:
> From: Guo Ren <guoren at linux.alibaba.com>
> 
> Some RISC-V CPU vendors have defined their own PTE attributes to
> solve non-coherent DMA bus problems. That makes _P/SXXX definitions
> contain global variables which could be initialized at the early
> boot stage before setup_vm. The patch prevents compile errors.

That sounds way to nice for someone who deliberatly ignores the
specification and should definitively not go into the kernel
commit log like this.

> This patch is similar to 316d097c4cd4  (x86/pti: Filter at
> vma->vm_page_prot population) which give a choice for arch custom
> implementation.

How?  To me it looks like a bad duplication of such functionality in
a way that totally breaks abstractions.  architectures really do not
have any business changing protection_map.