linux-kernel - Re: [PATCH v0 05/12] x86/mce: Allow instrumentation during task work queueing

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Date:   Tue, 9 Nov 2021 23:05:04 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tony Luck <tony.luck@...el.com>
Cc:     X86 ML <x86@...nel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v0 05/12] x86/mce: Allow instrumentation during task work
 queueing

On Thu, Nov 04, 2021 at 03:40:28PM +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> 
> Fixes
> 
>   vmlinux.o: warning: objtool: do_machine_check()+0xdb1: call to queue_task_work() leaves .noinstr.text section
> 
> Signed-off-by: Borislav Petkov <bp@...e.de>
> ---
>  arch/x86/kernel/cpu/mce/core.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/mce/core.c b/arch/x86/kernel/cpu/mce/core.c
> index c7181e8e2845..65a8be420aff 100644
> --- a/arch/x86/kernel/cpu/mce/core.c
> +++ b/arch/x86/kernel/cpu/mce/core.c
> @@ -1451,6 +1451,8 @@ noinstr void do_machine_check(struct pt_regs *regs)
>  	if (worst != MCE_AR_SEVERITY && !kill_current_task)
>  		goto out;
>  
> +	instrumentation_begin();

<peterz> so it might be nice to have a comment with each sandwich to
say why sh*t won't go sideways when instrumentation happens in the #MC
at that point
<peterz> like this shuts things up, but really we don't want
instrumentation here either, except blah

note to self: will need to go through the whole set.

-- 
Regards/Gruss,
    Boris.

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