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From:   Koba Ko <koba.ko@canonical.com>
Date:   Tue, 4 Jul 2023 12:59:15 +0800
Message-ID: <CAJB-X+XVO29wVxVezjFrgCyXigqEJxAzb0K0wueXNto5K_x2tA@mail.gmail.com>
Subject: Re: [PATCH v2] EDAC/i10nm: shift exponent is negative
To:     "Luck, Tony" <tony.luck@intel.com>
Cc:     Markus Elfring <Markus.Elfring@web.de>,
        "linux-edac@vger.kernel.org" <linux-edac@vger.kernel.org>,
        "kernel-janitors@vger.kernel.org" <kernel-janitors@vger.kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        James Morse <james.morse@arm.com>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Robert Richter <rric@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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As per suggestions, i modified V3.
could you please take a look

Subject: [PATCH][V3] EDAC/i10nm: shift exponent is negative

Because failed to read from DIMM, get the negative value for shift
operation.
`EDAC DEBUG: skx_get_dimm_attr: bad ranks =3D 3 (raw=3D0xffffffff)
 EDAC DEBUG: skx_get_dimm_attr: bad rows =3D 7 (raw=3D0xffffffff)
 EDAC DEBUG: skx_get_dimm_attr: bad cols =3D 3 (raw=3D0xffffffff)
 EDAC DEBUG: i10nm_get_dimm_config: dimmmtr 0xffffffff mcddrtcfg
0xffffffff (mc1 ch0 dimm1)`

UBSAN complains this error
`UBSAN: shift-out-of-bounds in drivers/edac/skx_common.c:369:16
 shift exponent -66 is negative`

when get rows, cols and ranks, the returned error value doesn't be
handled.

check the return value is EINVAL, if yes, directly return 0 and
show error message explicitly.

Fixes: 4ec656bdf43a13) EDAC, skx_edac: Add EDAC driver for Skylake
Signed-off-by: Koba Ko <koba.ko@canonical.com>
---
V2 -> V3: simplify the summary and add 'Fixes:'
V1 -> V2: make error-print explicitly

On Tue, Jul 4, 2023 at 10:20=E2=80=AFAM Koba Ko <koba.ko@canonical.com> wro=
te:
>
> On Tue, Jul 4, 2023 at 5:51=E2=80=AFAM Luck, Tony <tony.luck@intel.com> w=
rote:
> >
> > > > UBSAN complains this error
> > > > ~~~
> > > >  UBSAN: shift-out-of-bounds in drivers/edac/skx_common.c:369:16
> > > =E2=80=A6
> > > > ~~~
> > > >
> > > > when get rows, cols and ranks, the returned error value doesn't be
> > > > handled.
> > > >
> > > > check the return value is EINVAL, if yes, directly return 0.
> > > =E2=80=A6
> > >
> > > * Please improve this change description further.
> >
> > To be specific. Initially you reported this because of the UBSAN error
> > report. But, after community discussion you now know that the problem
> > is that one or more of the rows/cols/ranks has a value that the EDAC dr=
iver
> > doesn't expect and probably can handle.
> >
> > So, in V2, the commit message should start with the information these
> > values are out of range and mention this was discovered when UBSAN
> > put out a warning about a negative shift. No need to include the whole
> > of the UBSAN stack trace.
> >
> > Then describe the two fixes that this patch includes. One is to change =
the
> > edac debug message into a console error message to enable further
> > debug of this issue. The other is to skip the unrecognized DIMM.
> >
> > > * How do you think about to add the tag =E2=80=9CFixes=E2=80=9D?
> >
> > This is a good idea.  Use git blame, or dig into the GIT history to
> > find the commit where this code was introduced (hint .. git blame
> > says:
> > 88a242c98740 ("EDAC, skx_common: Separate common code out from skx_edac=
")
> > but that obviously just refactored code, so you should dig back more in=
to
> > the history.
> There are two parts,
> 1. @get_dimm_attr, edac_dbg was added since e235dd43d8b0f0
> 2. get num of ranks, rows and cols, 4ec656bdf43a13
>
> Should I add all of them prefixes with "Fixes"?
>
> >
> > > > V2: make error-print explicitly
> > > > ---
> > >
> > > Would you like to avoid a misplaced marker line here?
> > >
> > > See also:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tr=
ee/Documentation/process/submitting-patches.rst?h=3Dv6.4#n686
> >
> > That's an excellent resource.
> >
> > -Tony