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Date: Fri, 21 Apr 2017 13:50:50 -0700
From: "Luck, Tony" <tony.luck@intel.com>
Subject: Re: [PATCH] acpi, nfit: fix the memory error check in nfit_handle_mce
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To: Vishal Verma <vishal.l.verma@intel.com>
Cc: "linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>, "stable@vger.kernel.org" <stable@vger.kernel.org>, "linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>
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On Fri, Apr 21, 2017 at 02:35:51PM -0600, Vishal Verma wrote:
> On 04/21, Luck, Tony wrote:
> > Needs extra parentheses to make it right. Vishal, sorry I led you astray.
> > 
> > 	if (!((mce->status & 0xef80) == BIT(7)))
> 
> Is this still right though? Anything AND'ed with 0xef80 will never equal
> BIT(7) which is simply 01000000 binary (the lowest byte of the left hand
> side is '0')

I think so ... here it is in binary

ef80 = 1110 1111 1000 0000
BIT7 = 0000 0000 1000 0000

so the "&" will zap bits {6:0} and bit {12}  [and everything not part
of the MCACOD field].

If mce->status had some bit above BIT(7) set, it won't be zapped, so we
won't match the exact value BIT(7).

-Tony
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