linux-kernel - Re: xtensa question, was Re: [PATCH V1 00/10] Remove duplicated kmap code

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Message-ID: <CAMo8Bf+Mvvg_f1-33iQhTqZPVw1civX94KS2mf4uSkcpEVx55Q@mail.gmail.com>
Date:   Fri, 1 May 2020 02:02:19 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     ira.weiny@...el.com, LKML <linux-kernel@...r.kernel.org>,
        "open list:TENSILICA XTENSA PORT (xtensa)" 
        <linux-xtensa@...ux-xtensa.org>
Subject: Re: xtensa question, was Re: [PATCH V1 00/10] Remove duplicated kmap code

Hi Christoph,

On Fri, May 1, 2020 at 1:46 AM Christoph Hellwig <hch@...radead.org> wrote:
> any idea why xtensa uses PAGE_KERNEL_EXEC instead of PAGE_KERNEL
> for kmap_prot?  Mapping all mapped highmem as executable seems rather
> dangerous.

I sure do: to allow instruction cache flushing when writing to high user
pages temporarily mapped with kmap. Instruction cache management
opcodes that operate on virtual addresses would raise an exception if
the address is not executable.

-- 
Thanks.
-- Max