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From:   Kai-Heng Feng <kai.heng.feng@canonical.com>
Date:   Tue, 4 Jul 2023 12:27:39 +0800
Message-ID: <CAAd53p41Ku1m1rapeqb1xtD+kKuk+BaUW=dumuoF0ZO3GhFjFA@mail.gmail.com>
Subject: Re: [PATCH] EDAC/Intel: Fix shift-out-of-bounds when DIMM/NVDIMM is absent
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     "Zhuo, Qiuxu" <qiuxu.zhuo@intel.com>,
        "kao, acelan" <acelan.kao@canonical.com>,
        Borislav Petkov <bp@alien8.de>,
        James Morse <james.morse@arm.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Robert Richter <rric@kernel.org>,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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On Wed, Jun 14, 2023 at 3:58=E2=80=AFPM Kai-Heng Feng
<kai.heng.feng@canonical.com> wrote:
>
> On Wed, May 17, 2023 at 3:49=E2=80=AFPM Kai-Heng Feng
> <kai.heng.feng@canonical.com> wrote:
> >
> > On Wed, May 17, 2023 at 1:13=E2=80=AFAM Luck, Tony <tony.luck@intel.com=
> wrote:
> > >
> > > >> [   13.875282] Hardware name: HP HP Z4 G5 Workstation Desktop PC/8=
962,
> > > > > BIOS U61 Ver. 01.01.15 04/19/2023
> > >
> > >
> > > >> When a DIMM slot is empty, the read value of mtr can be 0xffffffff=
, therefore
> > >
> > > > Looked like a buggy BIOS/hw that didn't set the mtr register.
> > > >
> > > > 1. Did you print the mtr register whose value was 0xffffffff?
> > > > 2. Can you take a dmesg log with kernel "CONFIG_EDAC_DEBUG=3Dy" ena=
bled?
> > > > 3. What was the CPU? Please take the output of "lscpu".
> > > > 4. Did you verify your patch that the issue was fixed on your syste=
ms?
> > >
> > > I wonder if BIOS is "hiding" some devices from the OS? The 0xffffffff=
 return is
> > > the standard PCI response for reading a non-existent register. But th=
at doesn't
> > > quite make sense with having a "dimm present" bit in the MTR register=
. If
> > > the register only exists if the DIMM is present, then there is no nee=
d for
> > > a "dimm present" bit.
> >
> > I wonder if the "non-existent register" read is intended?
> >
> > >
> > > Some "lspci" output may also be useful.
> >
> > lspci can be found in [1]:
> >
> > [1] https://bugzilla.kernel.org/show_bug.cgi?id=3D217453
>
> A gentle ping...

Another gentle ping...

>
> >
> > Kai-Heng
> >
> > >
> > > -Tony