linux-kernel - Re: [PATCH 11/21] EDAC, ghes: Unify trace_mc_event() code with edac

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Message-ID: <37d47356-a40b-2739-10df-f5ab83fa2b36@arm.com>
Date:   Wed, 29 May 2019 16:12:38 +0100
From:   James Morse <james.morse@....com>
To:     Robert Richter <rrichter@...vell.com>
Cc:     Borislav Petkov <bp@...en8.de>, Tony Luck <tony.luck@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 11/21] EDAC, ghes: Unify trace_mc_event() code with
 edac_mc driver

Hi Robert,

On 29/05/2019 09:44, Robert Richter wrote:
> Almost duplicate code, remove it.

almost?

> Note: there is a difference in the calculation of the grain_bits,
> using the edac_mc's version here.

But is it the right thing to do?

Is this an off-by-one bug being papered over as some cleanup?
If so could you post a separate fix that can be picked up for an rc.

Do Marvell have firmware that populates this field?

...

Unless the argument is no one cares about this...

>From ghes_edac_report_mem_error():
|	/* Error grain */
|	if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK)
|		e->grain = ~(mem_err->physical_addr_mask & ~PAGE_MASK);

Fishy, why would the kernel page-size be relevant here?

If physical_addr_mask were the same as PAGE_MASK this wouldn't this always give ~0?
(masking logic like this always does my head in)

/me gives it ago:
| {1}[Hardware Error]:   physical_address: 0x00000000deadbeef
| {1}[Hardware Error]:   physical_address_mask: 0xffffffffffff0000
| {1}[Hardware Error]:   error_type: 6, master abort
| EDAC MC0: 1 CE Master abort on unknown label ( page:0xdead offset:0xbeef
| grain:-1 syndrome:0x0 - status(0x0000000000000001): reserved)

That 'grain:-1' is because the calculated e->grain was an unlikely 0xffffffffffffffff.
Patch incoming, if you could test it on your platform that'd be great.

I don't think ghes_edac.c wants this '+1'.

Thanks,

James