linux-kernel - Re: [PATCH] Revert "EDAC/mce_amd: Do not load edac_mce

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Message-ID: <fa5ec285-4d0f-4635-a35d-d290fd73ddfa@amd.com>
Date:   Wed, 13 Sep 2023 12:21:23 -0400
From:   Yazen Ghannam <yazen.ghannam@....com>
To:     "Luck, Tony" <tony.luck@...el.com>, Borislav Petkov <bp@...en8.de>,
        Elliott Mitchell <ehem+xen@....com>
Cc:     yazen.ghannam@....com,
        "smita.koralahallichannabasappa@....com" 
        <smita.koralahallichannabasappa@....com>,
        "linux-edac@...r.kernel.org" <linux-edac@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>,
        "xen-devel@...ts.xenproject.org" <xen-devel@...ts.xenproject.org>,
        "rric@...nel.org" <rric@...nel.org>,
        "james.morse@....com" <james.morse@....com>
Subject: Re: [PATCH] Revert "EDAC/mce_amd: Do not load edac_mce_amd module on
 guests"

On 9/13/23 11:50 AM, Luck, Tony wrote:
>> Also, please note that the EDAC modules don't handle MCE events
>> directly. They act on information passed from the MCE subsystem.
>>
>> Furthermore, there are other EDAC modules that have the same !hypervisor
>> check, so why change only this one?
> 
> The older Intel EDAC drivers translated system physical addresses to DIMM
> addresses by digging around in the CONFIG and MMIO space of the memory
> controller devices. It would seem unwise for a VMM to give access to those
> addresses to a guest (in general ... perhaps OK for a Xen style "DOM0" guest that is
> handling many tasks for the VMM?).
> 
> What system resources do AMD EDAC drivers need access to? Could they
> work inside a guest?
>

The MCE decoder may access some newer MCA registers, or request info
from the MCE subsystem. But this is for informational error decoding. It
won't support any actions that a guest could take.

The AMD64 EDAC module reads system-specific memory controller registers
through non-architectural interfaces. So also unwise or not useful for a
guest to access.

Thanks,
Yazen