linux-kernel - Re: [PATCH 09/11] x86/fault: Rename no_context() to kernelmode_fixup_or

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Date:   Wed, 3 Feb 2021 20:39:49 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Andy Lutomirski <luto@...nel.org>
Cc:     x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Yonghong Song <yhs@...com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 09/11] x86/fault: Rename no_context() to
 kernelmode_fixup_or_oops()

On Sun, Jan 31, 2021 at 09:24:40AM -0800, Andy Lutomirski wrote:
> The name no_context() has never been very clear.  It's only called for
> faults from kernel mode, so rename it and change the no-longer-useful
> user_mode(regs) check to a WARN_ON_ONCE.
> 
> Cc: Dave Hansen <dave.hansen@...ux.intel.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/mm/fault.c | 28 ++++++++++------------------
>  1 file changed, 10 insertions(+), 18 deletions(-)
> 
> diff --git a/arch/x86/mm/fault.c b/arch/x86/mm/fault.c
> index 177b612c7f33..04cc98ec2423 100644
> --- a/arch/x86/mm/fault.c
> +++ b/arch/x86/mm/fault.c
> @@ -693,17 +693,10 @@ page_fault_oops(struct pt_regs *regs, unsigned long error_code,
>  }
>  
>  static noinline void
> -no_context(struct pt_regs *regs, unsigned long error_code,
> -	   unsigned long address, int signal, int si_code)
> +kernelmode_fixup_or_oops(struct pt_regs *regs, unsigned long error_code,
> +			 unsigned long address, int signal, int si_code)

Ew, I don't like functions with "or" in the name - they're probably not
doing one thing only as they should.

Why not simply "handle_kernel_fault" ?

Also, all the callsites now do:

	if (!user_mode(regs)) {
		kernelmode_fixup_or_oops
		...

I guess you can push the "user_mode" check inside that function for less
hairy code at the callsites.

>  {
> -	if (user_mode(regs)) {
> -		/*
> -		 * This is an implicit supervisor-mode access from user
> -		 * mode.  Bypass all the kernel-mode recovery code and just
> -		 * OOPS.
> -		 */
> -		goto oops;
> -	}
> +	WARN_ON_ONCE(user_mode(regs));

I guess...

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette