Date:   Mon, 20 Dec 2021 19:56:55 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Lai Jiangshan <jiangshanlai@gmail.com>
Cc:     linux-kernel@vger.kernel.org, x86@kernel.org,
        Lai Jiangshan <laijs@linux.alibaba.com>,
        Andy Lutomirski <luto@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH 1/4] x86/entry: Make paranoid_exit() callable
Message-ID: <YcDR92+JFkVAZi5c@zn.tnic>
References: <20211213150340.9419-1-jiangshanlai@gmail.com>
 <20211213150340.9419-2-jiangshanlai@gmail.com>
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On Mon, Dec 13, 2021 at 11:03:37PM +0800, Lai Jiangshan wrote:
> From: Lai Jiangshan <laijs@linux.alibaba.com>
> 
> Move the last JMP out of paranoid_exit() and make it callable.
> 
> It will allow asm_exc_nmi() to call it and avoid duplicated code.
> 
> No functional change intended.
> 
> Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
> ---
>  arch/x86/entry/entry_64.S | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S
> index 44dadea935f7..3dc3cec03425 100644
> --- a/arch/x86/entry/entry_64.S
> +++ b/arch/x86/entry/entry_64.S
> @@ -439,7 +439,8 @@ SYM_CODE_START(\asmsym)
>  
>  	call	\cfunc
>  
> -	jmp	paranoid_exit
> +	call	paranoid_exit
> +	jmp	restore_regs_and_return_to_kernel

I guess but I don't like the glueing of the CALL to paranoid_exit with
the JMP to the restore_regs_and_return_to_kernel label. That reads
to me as, "if you're calling paranoid_exit() you must jump to the
restore_regs_and_return_to_kernel label but not always."

So I'm thinking you should leave the jump to that label inside
paranoid_exit() and use its %rbx argument to control when to jump to it
and when not.

I.e., not jump to it in the NMI case.

AFAICT, ofc. asm is always nasty to stare at.

Thx.

-- 
Regards/Gruss,
    Boris.

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