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

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Message-ID: <CAMuHMdXpW0re633tW9MsN-+A521Xytoicd-T0L7r7PAwJ-B0+Q@mail.gmail.com>
Date: Wed, 9 Jul 2025 11:36:27 +0200
From: Geert Uytterhoeven <geert@...ux-m68k.org>
To: "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc: Sohil Mehta <sohil.mehta@...el.com>, 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>, 
	Alexey Kardashevskiy <aik@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
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	Daniel Sneddon <daniel.sneddon@...ux.intel.com>, Kai Huang <kai.huang@...el.com>, 
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	"Masami Hiramatsu (Google)" <mhiramat@...nel.org>, Andrew Morton <akpm@...ux-foundation.org>, 
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	Rasmus Villemoes <linux@...musvillemoes.dk>, Christophe Leroy <christophe.leroy@...roup.eu>, 
	Tejun Heo <tj@...nel.org>, Changbin Du <changbin.du@...wei.com>, 
	Huang Shijie <shijie@...amperecomputing.com>, 
	Geert Uytterhoeven <geert+renesas@...der.be>, Namhyung Kim <namhyung@...nel.org>, 
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	linux-efi@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv9 11/16] x86/traps: Communicate a LASS violation in #GP message

Hi Kirill,

On Wed, 9 Jul 2025 at 11:31, Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
> 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.

arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT       32
arch/x86/include/asm/page_32_types.h:#define __VIRTUAL_MASK_SHIFT       32
arch/x86/include/asm/page_64_types.h:#define __VIRTUAL_MASK_SHIFT
 (pgtable_l5_enabled() ? 56 : 47)
arch/x86/include/asm/page_types.h:#define __VIRTUAL_MASK
 ((1UL << __VIRTUAL_MASK_SHIFT) - 1)

Given __VIRTUAL_MASK_SHIFT is 32 on 32-bit platforms, perhaps
__VIRTUAL_MASK should just be changed to shift 1ULL instead?
Or better, use GENMASK(__VIRTUAL_MASK_SHIFT - 1, 0), so the
resulting type is still unsigned long.

Gr{oetje,eeting}s,

                        Geert

-- 
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds