linux-kernel - Re: [PATCH] x86, tsc: Fix tsc ratio calibration to avoid broken mdelay

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Date:	Fri, 6 May 2016 11:53:25 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Chen Yu <yu.c.chen@...el.com>
cc:	x86@...nel.org, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, Bin Gao <bin.gao@...el.com>,
	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	"3 . 14+ # 3 . 14+" <stable@...r.kernel.org>
Subject: Re: [PATCH] x86, tsc: Fix tsc ratio calibration to avoid broken
 mdelay


On Fri, 6 May 2016, Thomas Gleixner wrote:
> On Fri, 6 May 2016, yu.c.chen@...el.com wrote:
> > From: Chen Yu <yu.c.chen@...el.com>
> > 
> > Currently we fetch the tsc radio by:
> > ratio = (lo >> 8) & 0x1f;
> > thus get bit8~bit12 of the MSR_PLATFORM_INFO, however according
> > to Intel 64 and IA-32 Architectures Software Developer Manual 35.5,
> > the ratio bit should be bit8~bit15, otherwise we might get incorrect
> > tsc ratio and cause system hang later(mdelay corrupted).
> 
> The resulting issue is that both TSC frequency, which is used for udelay, and
> the lapic timer frequency are wrong. mdelay is just the visible damage caused
> by that.

Aside of that:

> Cc: 3.14+ <stable@...r.kernel.org> # 3.14+

Please use:

Fixes: commit '....'

next time, which identifies the kernel version to which this needs to be
backported and gives a reference to the commit which caused the issue.

Thanks,

	tglx