linux-kernel - Re: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message

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Message-ID: <xy2ocwstdf44diw5p5hisjwvx467fyhm7bljz5xg72cmnhdfok@7pe3vmht6vcq>
Date: Wed, 9 Jul 2025 12:31:04 +0300
From: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
To: Sohil Mehta <sohil.mehta@...el.com>
Cc: Andy Lutomirski <luto@...nel.org>, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, 
	Peter Zijlstra <peterz@...radead.org>, Ard Biesheuvel <ardb@...nel.org>, 
	"Paul E. McKenney" <paulmck@...nel.org>, Josh Poimboeuf <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 <tony.luck@...el.com>, 
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	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org, 
	linux-mm@...ck.org
Subject: Re: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP
 message

On Tue, Jul 08, 2025 at 07:40:35PM -0700, Sohil Mehta wrote:
> > @@ -664,14 +673,23 @@ static enum kernel_gp_hint get_kernel_gp_address(struct pt_regs *regs,
> >  		return GP_NO_HINT;
> >  
> >  #ifdef CONFIG_X86_64
> 
> Might as well get rid of the #ifdef in C code, if possible.
> 
> if (!IS_ENABLED(CONFIG_X86_64)
> 	return GP_CANONICAL;
> 
> or combine it with the next check.

I tried this before. It triggers compiler error on 32-bit:

arch/x86/kernel/traps.c:673:16: error: shift count >= width of type [-Werror,-Wshift-count-overflow]
  673 |         if (*addr >= ~__VIRTUAL_MASK)
      |                       ^~~~~~~~~~~~~~

__VIRTUAL_MASK is not usable on 32-bit configs.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov