linux-kernel - Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the command line

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Message-ID: <b504f547-a1bf-3ba0-7fce-60bc48d89f65@ghiti.fr>
Date:   Tue, 31 Jan 2023 16:34:26 +0100
From:   Alexandre Ghiti <alex@...ti.fr>
To:     Alexandre Ghiti <alexghiti@...osinc.com>,
        Jonathan Corbet <corbet@....net>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Conor Dooley <conor@...nel.org>,
        Ard Biesheuvel <ardb@...nel.org>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH v4 0/1] riscv: Allow to downgrade paging mode from the
 command line

Sorry, I forgot the changelog again:

|v4: - Remove the kasan limitation by compiling 'local' fdt functions, 
as done in arm64 by Ard - Remove RB from Björn as the cmdline handling 
changed v3: - Massage commit log to make no4lvl clearer, as asked by 
Conor - Add a note to kernel-parameters.txt regarding the impossibility 
to use those parameters when KASAN is enabled, as suggested by Conor - 
Add RB from Björn v2: - Honor CMDLINE_EXTEND and CMDLINE_FORCE as 
noticed by Björn|

On 1/31/23 16:11, Alexandre Ghiti wrote:
> This new version gets rid of the limitation that prevented KASAN kernels
> to use the newly introduced parameters.
>
> While looking into KASLR, I fell onto commit aacd149b6238 ("arm64: head:
> avoid relocating the kernel twice for KASLR"): it allows to use the fdt
> functions very early in the boot process with KASAN enabled by simply
> compiling a new version of those functions without instrumentation.
>
> I had to change the handling of the command line parsing to make the
> code self-contained in kernel/pi/cmd_early.c to avoid calling too many
> __pi prefixed functions from outside this file.
>
> I'll use this approach like arm64 to handle the extraction of the random
> seedi from the device tree for KASLR.
>
> @Ard: I copied the "pi" name but I have to admit I don't know what it
> means.
>
> Alexandre Ghiti (1):
>    riscv: Allow to downgrade paging mode from the command line
>
>   .../admin-guide/kernel-parameters.txt         |  5 +-
>   arch/riscv/kernel/Makefile                    |  2 +
>   arch/riscv/kernel/pi/Makefile                 | 34 ++++++++++++
>   arch/riscv/kernel/pi/cmdline_early.c          | 52 +++++++++++++++++++
>   arch/riscv/lib/memcpy.S                       |  2 +
>   arch/riscv/lib/memmove.S                      |  2 +
>   arch/riscv/mm/init.c                          | 36 ++++++++++---
>   7 files changed, 126 insertions(+), 7 deletions(-)
>   create mode 100644 arch/riscv/kernel/pi/Makefile
>   create mode 100644 arch/riscv/kernel/pi/cmdline_early.c
>