linux-kernel - Re: [PATCHv8 13/17] x86/traps: Generalize #GP address decode and hint code

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Message-ID: <d777b118-68d1-4212-a33e-d129d777515f@intel.com>
Date: Tue, 1 Jul 2025 17:54:44 -0700
From: Sohil Mehta <sohil.mehta@...el.com>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>, Andy Lutomirski
	<luto@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar
	<mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen
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	<jpoimboe@...nel.org>, Xiongwei Song <xiongwei.song@...driver.com>, Xin Li
	<xin3.li@...el.com>, "Mike Rapoport (IBM)" <rppt@...nel.org>, Brijesh Singh
	<brijesh.singh@....com>, Michael Roth <michael.roth@....com>, Tony Luck
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	<alexander.shishkin@...ux.intel.com>
CC: Jonathan Corbet <corbet@....net>, Ingo Molnar <mingo@...nel.org>, "Pawan
 Gupta" <pawan.kumar.gupta@...ux.intel.com>, Daniel Sneddon
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	<linux-efi@...r.kernel.org>, <linux-mm@...ck.org>
Subject: Re: [PATCHv8 13/17] x86/traps: Generalize #GP address decode and hint
 code

On 7/1/2025 2:58 AM, Kirill A. Shutemov wrote:
> Handlers for #GP and #SS will now share code to decode the exception
> address and retrieve the exception hint string.
> 

This is missing an essential "why"? Why do #GP and #SS handlers need to
share code? None of the patches prior to this have hinted this.

It can probably be deduced from a later patch, but it needs to be
clarified in this one. Maybe a simplified version of the text from the SDM:

"In most cases, an access causing a LASS violation results in a general
protection exception (#GP); for stack accesses (those due to
stack-oriented instructions, as well as accesses that implicitly or
explicitly use the SS segment register), a stack fault (#SS) is generated."

> The helper, enum, and array should be renamed as they are no longer
> specific to #GP.
> 
> No functional change intended.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  arch/x86/kernel/traps.c | 62 ++++++++++++++++++++---------------------
>  1 file changed, 31 insertions(+), 31 deletions(-)
> 

The code changes look okay to me except a minor nit below.

>  #define GPFSTR "general protection fault"
> @@ -808,8 +808,8 @@ static void gp_user_force_sig_segv(struct pt_regs *regs, int trapnr,
>  DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
>  {
>  	char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;
> -	enum kernel_gp_hint hint = GP_NO_HINT;
> -	unsigned long gp_addr;

gp_addr is a local variable to the #GP handler. It can probably stay the
same.

> +	enum kernel_exc_hint hint = EXC_NO_HINT;
> +	unsigned long exc_addr;
>  
>  	if (user_mode(regs) && try_fixup_enqcmd_gp())
>  		return;
> @@ -846,21 +846,21 @@ DEFINE_IDTENTRY_ERRORCODE(exc_general_protection)
>  	if (error_code)
>  		snprintf(desc, sizeof(desc), "segment-related " GPFSTR);
>  	else
> -		hint = get_kernel_gp_address(regs, &gp_addr);
> +		hint = get_kernel_exc_address(regs, &exc_addr);
>  
> -	if (hint != GP_NO_HINT) {
> +	if (hint != EXC_NO_HINT) {
>  		snprintf(desc, sizeof(desc), GPFSTR ", %s 0x%lx",
> -			 kernel_gp_hint_help[hint], gp_addr);
> +			 kernel_exc_hint_help[hint], exc_addr);
>  	}
>  
>  	/*
>  	 * KASAN is interested only in the non-canonical case, clear it
>  	 * otherwise.
>  	 */
> -	if (hint != GP_NON_CANONICAL)
> -		gp_addr = 0;
> +	if (hint != EXC_NON_CANONICAL)
> +		exc_addr = 0;
>  
> -	die_addr(desc, regs, error_code, gp_addr);
> +	die_addr(desc, regs, error_code, exc_addr);
>  
>  exit:
>  	cond_local_irq_disable(regs);