Re: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs

From: Borislav Petkov <bp@alien8.de>
To: ira.weiny@intel.com
Cc: Rik van Riel <riel@surriel.com>,
	Dave Hansen <dave.hansen@intel.com>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com
Subject: Re: [RFC PATCH 2/5] entry: Add calls for save/restore auxiliary pt_regs
Date: Tue, 9 Aug 2022 14:05:15 +0200	[thread overview]
Message-ID: <YvJNe2rzXfcogFFX@zn.tnic> (raw)
In-Reply-To: <20220805173009.3128098-3-ira.weiny@intel.com>

On Fri, Aug 05, 2022 at 10:30:06AM -0700, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
> 
> Some architectures have auxiliary pt_regs space available to store
> information on the stack during exceptions.  This information is easier
> to obtain and store within C code rather than in arch specific assembly.

There are others?

Because I would've done this whole thing in arch/x86/ only...

> diff --git a/kernel/entry/common.c b/kernel/entry/common.c
> index 8c0f334c4b75..a70a0f314aee 100644
> --- a/kernel/entry/common.c
> +++ b/kernel/entry/common.c
> @@ -317,7 +317,7 @@ noinstr irqentry_state_t irqentry_enter(struct pt_regs *regs)
>  
>  	if (user_mode(regs)) {
>  		irqentry_enter_from_user_mode(regs);
> -		return ret;
> +		goto aux_save;

Why do you have to goto and do the instrumentation sandwitch around it
at the goto label?

Why not simply do

	if (user_mode(regs)) {
		irqentry_enter_from_user_mode(regs);
		arch_save_aux_pt_regs(regs);
		return ret;

and so on?

Thx.

-- 
Regards/Gruss,
    Boris.

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