linux-kernel - Re: [PATCH] x86/asm: Use asm_inline() instead of asm() in amd_clear

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Message-ID: <CAFULd4a5V3b6gfahGNsU7nHVki7Asnd-+t9NhV6NiE_8FYCpGw@mail.gmail.com>
Date: Thu, 13 Mar 2025 21:11:31 +0100
From: Uros Bizjak <ubizjak@...il.com>
To: Borislav Petkov <bp@...en8.de>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, 
	Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...nel.org>, 
	Dave Hansen <dave.hansen@...ux.intel.com>, "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH] x86/asm: Use asm_inline() instead of asm() in amd_clear_divider()

On Thu, Mar 13, 2025 at 9:07 PM Borislav Petkov <bp@...en8.de> wrote:

> >> > static __always_inline void amd_clear_divider(void)
> >> > {
> >> >-      asm volatile(ALTERNATIVE("", "div %2\n\t", X86_BUG_DIV0)
> >> >+      asm_inline volatile(ALTERNATIVE("", "div %2", X86_BUG_DIV0)
> >> >                    :: "a" (0), "d" (0), "r" (1));
> >> > }
> >> >
> >>
> >> So there's no point for this one...
> >
> >Not at its current usage sites, but considering that
> >amd_clear_divider() and two levels of small functions that include it
> >( amd_clear_divider(), arch_exit_to_user_mode() and
> >exit_to_user_mode() ) all need to be decorated with __always_inline
> >indicates that the issue is not that benign.
> >
> >It also triggers my search scripts, so I thought I should convert this
> >one as well and put the issue at rest.
>
> Sorry but this doesn't justify this churn. There's nothing quantifyingly palpable here to warrant this.

OK. This is not a hill I'm willing to die on.

Thanks,
Uros.