linux-kernel - RE: [PATCH] ACPI: APEI: set memory failure flags as MF_ACTION

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Message-ID: <SJ1PR11MB60839264AEF656759C8C56D1FC329@SJ1PR11MB6083.namprd11.prod.outlook.com>
Date:   Fri, 28 Oct 2022 17:25:30 +0000
From:   "Luck, Tony" <tony.luck@...el.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>,
        Shuai Xue <xueshuai@...ux.alibaba.com>
CC:     "lenb@...nel.org" <lenb@...nel.org>,
        "james.morse@....com" <james.morse@....com>,
        "bp@...en8.de" <bp@...en8.de>,
        "dave.hansen@...ux.intel.com" <dave.hansen@...ux.intel.com>,
        "jarkko@...nel.org" <jarkko@...nel.org>,
        "naoya.horiguchi@....com" <naoya.horiguchi@....com>,
        "linmiaohe@...wei.com" <linmiaohe@...wei.com>,
        "akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "cuibixuan@...ux.alibaba.com" <cuibixuan@...ux.alibaba.com>,
        "baolin.wang@...ux.alibaba.com" <baolin.wang@...ux.alibaba.com>,
        "zhuo.song@...ux.alibaba.com" <zhuo.song@...ux.alibaba.com>
Subject: RE: [PATCH] ACPI: APEI: set memory failure flags as
 MF_ACTION_REQUIRED on action required events

>> cper_sec_mem_err::error_type identifies the type of error that occurred
>> if CPER_MEM_VALID_ERROR_TYPE is set. So, set memory failure flags as 0
>> for Scrub Uncorrected Error (type 14). Otherwise, set memory failure
>> flags as MF_ACTION_REQUIRED.

On x86 the "action required" cases are signaled by a synchronous machine check
that is delivered before the instruction that is attempting to consume the uncorrected
data retires. I.e., it is guaranteed that the uncorrected error has not been propagated
because it is not visible in any architectural state.

APEI signaled errors don't fall into that category on x86 ... the uncorrected data
could have been consumed and propagated long before the signaling used for
APEI can alert the OS.

Does ARM deliver APEI signals synchronously?

If not, then this patch might deliver a false sense of security to applications
about the state of uncorrected data in the system.

-Tony