linux-kernel - Re: [PATCHv9 13/16] x86/traps: Handle LASS thrown #SS

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Message-ID: <j76lggwdlxv3lbs7iaqny42ay3m4qqwjnf6vqgesaykpozciaj@a2azdryhmaig>
Date: Wed, 9 Jul 2025 13:38:49 +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>, 
	Alexey Kardashevskiy <aik@....com>, Alexander Shishkin <alexander.shishkin@...ux.intel.com>, 
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	Yuntao Wang <ytcoode@...il.com>, Rasmus Villemoes <linux@...musvillemoes.dk>, 
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	Huang Shijie <shijie@...amperecomputing.com>, Geert Uytterhoeven <geert+renesas@...der.be>, 
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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 13/16] x86/traps: Handle LASS thrown #SS

On Tue, Jul 08, 2025 at 10:12:28PM -0700, Sohil Mehta wrote:
> On 7/7/2025 1:03 AM, Kirill A. Shutemov wrote:
> 
> > +	hint = get_kernel_exc_address(regs, &exc_addr);
> > +	if (hint != EXC_NO_HINT)
> > +		printk(SSFSTR ", %s 0x%lx", kernel_exc_hint_help[hint], exc_addr);
> > +
> > +	if (hint != EXC_NON_CANONICAL)
> > +		exc_addr = 0;
> > +
> > +	die_addr(SSFSTR, regs, error_code, exc_addr);
> 
> I see a slight difference between the #GP handling and the #SS handling
> here. For the #GP case, we seem to pass the hint string to die_addr().
> 
> However, for the #SS, the hint is printed above and only SSFSTR gets
> passed onto die_addr(). I am curious about the reasoning.

I hate how 'desc' size is defined in #GP handler:

	char desc[sizeof(GPFSTR) + 50 + 2*sizeof(unsigned long) + 1] = GPFSTR;

Too much voodoo to my liking. And it will overflow if any hint string is
going to be longer than 50.

I don't want to repeat this magic for #SS.

I would argue we need to print directly in #GP handler as I do in #SS.
But, IMO, it is outside of the scope of this patchset.

-- 
  Kiryl Shutsemau / Kirill A. Shutemov