Message-ID: <75dedf3a-41c7-980e-a8a8-74d116ae6663@linux.alibaba.com>
Date:   Fri, 24 Dec 2021 16:55:46 +0800
From:   Shuai Xue <xueshuai@...ux.alibaba.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>
Cc:     bp@...en8.de, tony.luck@...el.com, james.morse@....com,
        lenb@...nel.org, bhelgaas@...gle.com,
        zhangliguang@...ux.alibaba.com, zhuo.song@...ux.alibaba.com,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org
Subject: Re: [RESEND PATCH v4] ACPI: Move sdei_init and ghes_init ahead to
 handle platform errors earlier

Hi, Bjorn,

Thank you for your comments.

在 2021/12/24 AM8:17, Bjorn Helgaas 写道:
> [+to Rafael, question about HEST/GHES/SDEI init]
> 
> On Thu, Dec 23, 2021 at 04:11:11PM +0800, Shuai Xue wrote:
>> 在 2021/12/22 AM7:17, Bjorn Helgaas 写道:
>>> On Thu, Dec 16, 2021 at 09:34:56PM +0800, Shuai Xue wrote:
>>>> On an ACPI system, ACPI is initialised very early from a subsys_initcall(),
>>>> while SDEI is not ready until a subsys_initcall_sync().
>>>>
>>>> The SDEI driver provides functions (e.g. apei_sdei_register_ghes,
>>>> apei_sdei_unregister_ghes) to register or unregister event callback for
>>>> dispatcher in firmware. When the GHES driver probing, it registers the
>>>> corresponding callback according to the notification type specified by
>>>> GHES. If the GHES notification type is SDEI, the GHES driver will call
>>>> apei_sdei_register_ghes to register event call.
>>>>
>>>> When the firmware emits an event, it migrates the handling of the event
>>>> into the kernel at the registered entry-point __sdei_asm_handler. And
>>>> finally, the kernel will call the registered event callback and return
>>>> status_code to indicate the status of event handling. SDEI_EV_FAILED
>>>> indicates that the kernel failed to handle the event.
>>>>
>>>> Consequently, when an error occurs during kernel booting, the kernel is
>>>> unable to handle and report errors until the GHES driver is initialized by
>>>> device_initcall(), in which the event callback is registered. All errors
>>>> that occurred before GHES initialization are missed and there is no chance
>>>> to report and find them again.
>>>>
>>>> From commit e147133a42cb ("ACPI / APEI: Make hest.c manage the estatus
>>>> memory pool") was merged, ghes_init() relies on acpi_hest_init() to manage
>>>> the estatus memory pool. On the other hand, ghes_init() relies on
>>>> sdei_init() to detect the SDEI version and the framework for registering
>>>> and unregistering events.
>>>
>>>> By the way, I don't figure out why acpi_hest_init is called in
>>>> acpi_pci_root_init, it don't rely on any other thing. May it could
>>>> be moved further, following acpi_iort_init in acpi_init.
> 
>>>> sdei_init() relies on ACPI table which is initialized
>>>> subsys_initcall(): acpi_init(), acpi_bus_init(), acpi_load_tables(),
>>>> acpi_tb_laod_namespace().  May it should be also moved further,
>>>> after acpi_load_tables.
> 
>>>> In this patch, move sdei_init and ghes_init as far ahead as
>>>> possible, right after acpi_hest_init().
>>>
>>> I'm having a hard time figuring out the reason for this patch.
>>>
>>> Apparently the relevant parts are sdei_init() and ghes_init().
>>> Today they are executed in that order:
>>>
>>>   subsys_initcall_sync(sdei_init);
>>>   device_initcall(ghes_init);
>>>
>>> After this patch, they would be executed in the same order, but called
>>> explicitly instead of as initcalls:
>>>
>>>   acpi_pci_root_init()
>>>   {
>>>     acpi_hest_init();
>>>     sdei_init();
>>>     ghes_init();
>>>     ...
>>>
>>> Explicit calls are certainly better than initcalls, but that doesn't
>>> seem to be the reason for this patch.
>>>
>>> Does this patch fix a bug?  If so, what is the bug?
>>
>> Yes. When the kernel booting, the console logs many times from firmware
>> before GHES drivers init:
>>
>> 	Trip in MM PCIe RAS handle(Intr:910)
>>   	Clean PE[1.1.1] ERR_STS:0x4000100 -> 0 INT_STS:F0000000
>> 	Find RP(98:1.0)
>> 	--Walk dev(98:1.0) CE:0 UCE:4000
>> 	...
>> 	ERROR:   sdei_dispatch_event(32a) ret:-1
>> 	--handler(910) end
>>
>> This is because the callback function has not been registered yet.
>> Previously reported errors will be overwritten by new ones. Therefore,
>> all errors that occurred before GHES initialization are missed
>> and there is no chance to report and find them again.
>>
>>> You say that currently "errors that occur before GHES initialization
>>> are missed".  Isn't that still true after this patch?  Does this patch
>>> merely reduce the time before GHES initialization?  If so, I'm
>>> dubious, because we have to tolerate an arbitrary amount of time
>>> there.
>>
>> After this patch, there are still errors missing. As you mentioned,
>> we have to tolerate it until the software reporting capability is built.
>>
>> Yes, this patch merely reduce the time before GHES initialization.
> 
> It's not a bug that errors that happen before the callback are lost.
> At least, it's not a *Linux* bug.  It might be a poor design of the
> firmware error reporting interface.
>
> If the only point of this patch is to reduce the time before GHES
> initialization, the commit log should clearly say that.

Yep, it is a design defect of firmware. I will explicitly document
the purpose of this patch in next version.

>> The boot dmesg before this patch:
>>
>> 	[    3.688586] HEST: Table parsing has been initialized.
>> 	...
>> 	[   33.204340] calling  sdei_init+0x0/0x120 @ 1
>> 	[   33.208645] sdei: SDEIv1.0 (0x0) detected in firmware.
>> 	...
>> 	[   36.005390] calling  ghes_init+0x0/0x11c @ 1
>> 	[   36.190021] GHES: APEI firmware first mode is enabled by APEI bit and WHEA _OSC.
>>
>>
>> After this patch, the boot dmesg like bellow:
>>
>> 	[    3.688664] HEST: Table parsing has been initialized.
>> 	[    3.688691] sdei: SDEIv1.0 (0x0) detected in firmware.
>> 	[    3.694557] GHES: APEI firmware first mode is enabled by APEI bit and WHEA _OSC.

After this patch, we use explicit call to init GHES rather than initcall.
The GHES message here is just to prove that GHES initialization is
advanced to 3.694557 seconds.


> [Tangent: I think this GHES message is confusing.  What "APEI bit"
> does this refer to?  The only bits I remember are the Flags bits in
> HEST Error Source Descriptor Entries, e.g., ACPI v6.3, sec 18.3.2.

>From the log code behavior, the APEI bit refers to OSC_SB_APEI_SUPPORT.
(BIT 4, ACPI v6.4, sec 6.2.11.2,  table Table 6.13 Platform-Wide _OSC
Capabilities DWORD 2. [1])

    /* code in drivers/acpi/apei/ghes.c */
    if (rc == 0 && osc_sb_apei_support_acked)
        pr_info(GHES_PFX "APEI firmware first mode is enabled by APEI bit and WHEA _OSC.\n");

    /* code in drivers/acpi/bus.c */
    osc_sb_apei_support_acked =
        capbuf_ret[OSC_SUPPORT_DWORD] & OSC_SB_APEI_SUPPORT;


> "WHEA _OSC" means nothing to me, and I didn't find anything useful
> with grep, other than that "WHEA" might be an obsolete name for what
> we now call "APEI".

Yep, WHEA is an obsolete name. I think apei_osc_setup() is added for compatibility
in commit eccddd32ced0 ("ACPI, APEI, Add APEI bit support in generic _OSC call")'

The ACPI spec Platform-Wide OSPM Capabilities defines
UUID "0811B06E-4A27-44F9-8D60-3CBBC22E7B48" is used in
acpi_bus_osc_support(). The Microsoft WHEA defines
UUID "ed855e0c-6c90-47bf-a62a-26de0fc5ad5c" that is used
in apei_osc_setup(). [2][3]

>From the discussion[4], the GHES message is to distinguish between
the two specs.

    To avoid confusion, can we change the message as follow.

    - generic _OSC succeeded, APEI _OSC failed: APEI firmware first mode is
    enabled by APEI bit.
    - generic _OSC failed, APEI _OSC succeeded: APEI firmware first mode is
    enabled by WHEA _OSC.
    - both succeeded: APEI firmware first mode is enabled by APEI bit and
    WHEA _OSC.
    - both failed: Failed to enable APEI firmware first mode!


> I don't think there's anything in _OSC that mentions "firmware first."
>
> I don't remember anything in the spec about a way to *enable* Firmware
> First Error Handling needing (I'm looking at ACPI v6.3, sec 18.4).
> 
> I think the "firmware first" information is useless to the OS -- as
> far as I can tell, the spec says nothing about anything the OS should
> do based on the FIRMWARE_FIRST bits.]

GHES works in "Firmware First" mode to report platform hardware error
and it depends on APEI interface. (drivers/acpi/apei/ghes.c)

   * Generic Hardware Error Source provides a way to report platform
   * hardware errors (such as that from chipset). It works in so called
   * "Firmware First" mode, that is, hardware errors are reported to
   * firmware firstly, then reported to Linux by firmware.

Based on above, I think the GHES message just means that this booting
kernel supports APEI or WHEA, and GHES report Firmware first errors on
this machine. Is it fine to keep the message?


>> As we can see, the initialization of GHES is advanced by 33 seconds.
>> So, in my opinion, this patch is necessary, right?
>> (It should be noted that the effect of optimization varies with the platform.)
> 
>>>> -device_initcall(ghes_init);
>>>
>>>>  void __init acpi_pci_root_init(void)
>>>>  {
>>>>  	acpi_hest_init();
>>>> +	sdei_init();
>>>> +	ghes_init();
>>>
>>> What's the connection between PCI, SDEI, and GHES?  As far as I can
>>> tell, SDEI and GHES are not PCI-specific, so it doesn't seem like they
>>> should be initialized here in acpi_pci_root_init().
>>
>> The only reason is that acpi_hest_init() is initialized here.
>>
>> From commit e147133a42cb ("ACPI / APEI: Make hest.c manage the estatus
>> memory pool") was merged, ghes_init() relies on acpi_hest_init() to manage
>> the estatus memory pool. On the other hand, ghes_init() relies on
>> sdei_init() to detect the SDEI version and the framework for registering
>> and unregistering events. The dependencies are as follows
>>
>> 	ghes_init() => acpi_hest_init()
>> 	ghes_init() => sdei_init()
>>
>> I don't figure out why acpi_hest_init() is called in
>> acpi_pci_root_init(), it don't rely on any other thing.
>> I am wondering that should we moved all of them further? e.g.
>> following acpi_iort_init() in acpi_init().
> 
> I don't know why acpi_hest_init() is called from acpi_pci_root_init().
> It looks like HEST can support error sources other than PCI (IA-32
> Machine Checks, NMIs, GHES, etc.)  It was added by 415e12b23792
> ("PCI/ACPI: Request _OSC control once for each root bridge (v3)");
> maybe Rafael remembers why.
> 
> Seem like acpi_hest_init(), sdei_init(), and ghes_init() should all go
> somewhere else, but I don't know where.  Maybe somewhere in
> acpi_init()?

I tried to move them into acpi_init(), and it works well.

@@ -1251,6 +1251,9 @@ static int __init acpi_init(void)

        pci_mmcfg_late_init();
        acpi_iort_init();
+       acpi_hest_init();
+       sdei_init();
+       ghes_init();
        acpi_scan_init();
        acpi_ec_init();

What's your opinion?

Best Regards,

Shuai


[1] https://uefi.org/specs/ACPI/6.4/06_Device_Configuration/Device_Configuration.html#platform-wide-osc-capabilities-dword-2
[2] https://www.mail-archive.com/ubuntu-bugs@lists.ubuntu.com/msg4718503.html
[3] http://www.guyreams.com/PDF/whea.pdf
[4] https://patchwork.kernel.org/project/linux-acpi/patch/1308640587-24502-5-git-send-email-ying.huang@intel.com/#1978922

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