linux-kernel - Re: [PATCH 0/5] x86: Cleanups around slow_down

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Message-ID: <55bedecf-a4ab-445d-b6b2-c6dcbcd5bd95@roeck-us.net>
Date: Wed, 26 Nov 2025 09:08:15 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
 x86@...nel.org, virtualization@...ts.linux.dev, kvm@...r.kernel.org,
 linux-hwmon@...r.kernel.org, linux-block@...r.kernel.org
Cc: Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>,
 Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>,
 "H. Peter Anvin" <hpa@...or.com>, Ajay Kaher <ajay.kaher@...adcom.com>,
 Alexey Makhalov <alexey.makhalov@...adcom.com>,
 Broadcom internal kernel review list
 <bcm-kernel-feedback-list@...adcom.com>, Paolo Bonzini
 <pbonzini@...hat.com>, Vitaly Kuznetsov <vkuznets@...hat.com>,
 Boris Ostrovsky <boris.ostrovsky@...cle.com>,
 xen-devel@...ts.xenproject.org, Jean Delvare <jdelvare@...e.com>,
 Denis Efremov <efremov@...ux.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 0/5] x86: Cleanups around slow_down_io()

On 11/26/25 08:20, Juergen Gross wrote:
> While looking at paravirt cleanups I stumbled over slow_down_io() and
> the related REALLY_SLOW_IO define.
> 
> Especially REALLY_SLOW_IO is a mess, which is proven by 2 completely
> wrong use cases.
> 
> Do several cleanups, resulting in a deletion of REALLY_SLOW_IO and the
> io_delay() paravirt function hook.
> 
> Patches 2 and 3 are not changing any functionality, but maybe they
> should? As the potential bug has been present for more than a decade
> now, I went with just deleting the useless "#define REALLY_SLOW_IO".
> The alternative would be to do something similar as in patch 5.

Maybe, but as you point out there has not been a report of a problem
for a long time (who knows if any of the affected systems still exist).
We can apply always apply a fix if it turns out that someone does run
into a problem.

Thanks,
Guenter