linux-kernel - Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div

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Message-ID: <20250724081125.GA10980@redhat.com>
Date: Thu, 24 Jul 2025 10:11:26 +0200
From: Oleg Nesterov <oleg@...hat.com>
To: David Laight <david.laight.linux@...il.com>
Cc: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"Li,Rongqing" <lirongqing@...du.com>,
	Steven Rostedt <rostedt@...dmis.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org
Subject: Re: [PATCH] x86/math64: handle #DE in mul_u64_u64_div_u64()

On 07/23, David Laight wrote:
>
> On Wed, 23 Jul 2025 11:38:25 +0200
> Oleg Nesterov <oleg@...hat.com> wrote:
> >
> > to remove the conditional branch and additional variable. Your version
> > is probably beterr... But this is without WARN/BUG.
>
> I wish there was a way of doing a WARN_ONCE from asm with a single instruction.
> Then you could put one after your 2:
> Otherwise is it a conditional and a load of inlined code.
>
> > So, which version do you prefer?
>
> I wish I knew :-)

;-)

David, you understand this asm magic indefinitely better than me. Plus you are
working on the generic code. Can you send the patch which looks right to you?
I agree in advance with anything you do.

I got lost. Now I don't even understand if we want to add BUG and/or WARN into
mul_u64_u64_div_u64().

Thanks,

Oleg.