linux-kernel - Re: [PATCH v5 3/9] x86/head: Move early exception panic code into early_fixup

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Message-ID: <20160402183919.GA2538@pd.tnic>
Date:	Sat, 2 Apr 2016 20:39:19 +0200
From:	Borislav Petkov <bp@...en8.de>
To:	Andy Lutomirski <luto@...nel.org>
Cc:	X86 ML <x86@...nel.org>, Paolo Bonzini <pbonzini@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	KVM list <kvm@...r.kernel.org>,
	Arjan van de Ven <arjan@...ux.intel.com>,
	xen-devel <Xen-devel@...ts.xen.org>,
	linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v5 3/9] x86/head: Move early exception panic code into
 early_fixup_exception

On Sat, Apr 02, 2016 at 07:01:34AM -0700, Andy Lutomirski wrote:
> This removes a bunch of assembly and adds some C code instead.  It
> changes the actual printouts on both 32-bit and 64-bit kernels, but
> they still seem okay.
> 
> Signed-off-by: Andy Lutomirski <luto@...nel.org>
> ---
>  arch/x86/include/asm/uaccess.h |  2 +-
>  arch/x86/kernel/head_32.S      | 49 +++++-------------------------------------
>  arch/x86/kernel/head_64.S      | 45 ++------------------------------------
>  arch/x86/mm/extable.c          | 29 ++++++++++++++++++++-----
>  4 files changed, 32 insertions(+), 93 deletions(-)

...

> @@ -99,21 +101,38 @@ int __init early_fixup_exception(struct pt_regs *regs, int trapnr)
>  
>  	/* Ignore early NMIs. */
>  	if (trapnr == X86_TRAP_NMI)
> -		return 1;
> +		return;
> +
> +	if (early_recursion_flag > 2)
> +		goto halt_loop;
> +
> +	if (regs->cs != __KERNEL_CS)
> +		goto fail;
>  
>  	e = search_exception_tables(regs->ip);
>  	if (!e)
> -		return 0;
> +		goto fail;
>  
>  	new_ip  = ex_fixup_addr(e);
>  	handler = ex_fixup_handler(e);
>  
>  	/* special handling not supported during early boot */
>  	if (handler != ex_handler_default)
> -		return 0;
> +		goto fail;
>  
>  	regs->ip = new_ip;
> -	return 1;
> +	return;
> +
> +fail:
> +	early_printk("PANIC: early exception 0x%02x IP %lx:%lx error %lx cr2 0x%lx\n",
> +		     (unsigned)trapnr, (unsigned long)regs->cs, regs->ip,
> +		     regs->orig_ax, read_cr2());
> +
> +	show_regs(regs);

To make this even better, it could be something called early_show_regs()
or so and be a simplified version of __show_regs() on both bitness but
which calls early_printk().

This way you'll be able to get out stuff to the console as early as
possible.

Btw, you don't need to dump rIP, CR2, etc in the PANIC message above
since you're going to early_show_regs() anyway.

-- 
Regards/Gruss,
    Boris.

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