linux-kernel - Re: [RFC PATCH V4 1/6] riscv: pgtable: Add custom protection

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Message-ID: <20210915074557.GA20024@lst.de>
Date:   Wed, 15 Sep 2021 09:45:57 +0200
From:   Christoph Hellwig <hch@....de>
To:     guoren@...nel.org
Cc:     anup.patel@....com, atish.patra@....com, palmerdabbelt@...gle.com,
        christoph.muellner@...ll.eu, philipp.tomsich@...ll.eu, hch@....de,
        liush@...winnertech.com, wefu@...hat.com, lazyparser@...il.com,
        drew@...gleboard.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, taiten.peng@...onical.com,
        aniket.ponkshe@...onical.com, heinrich.schuchardt@...onical.com,
        gordan.markus@...onical.com, Guo Ren <guoren@...ux.alibaba.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Palmer Dabbelt <palmer@...belt.com>
Subject: Re: [RFC PATCH V4 1/6] riscv: pgtable: Add custom protection_map
 init

On Sat, Sep 11, 2021 at 05:21:34PM +0800, guoren@...nel.org wrote:
> From: Guo Ren <guoren@...ux.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.