[+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:

quoted

On Thu, Dec 16, 2021 at 09:34:56PM +0800, Shuai Xue wrote:

quoted

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.

quoted

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.

quoted

quoted

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.

quoted

quoted

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.

quoted

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.

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.

[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.

"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".

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.]

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.)

quoted

quoted

-device_initcall(ghes_init);

quoted

 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()?

Bjorn

_______________________________________________
linux-arm-kernel mailing list
linux-arm-kernel@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-arm-kernel