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Date:   Tue, 18 Jan 2022 16:49:35 -0600
From:   Bjorn Helgaas <helgaas@kernel.org>
To:     Shuai Xue <xueshuai@linux.alibaba.com>
Cc:     rafael@kernel.org, bp@alien8.de, tony.luck@intel.com,
        james.morse@arm.com, lenb@kernel.org, rjw@rjwysocki.net,
        bhelgaas@google.com, zhangliguang@linux.alibaba.com,
        zhuo.song@linux.alibaba.com, linux-kernel@vger.kernel.org,
        linux-acpi@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
        linux-pci@vger.kernel.org
Subject: Re: [PATCH v5] ACPI: Move sdei_init and ghes_init ahead to handle
 platform errors earlier
Message-ID: <20220118224935.GA903617@bhelgaas>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20220116084310.57465-1-xueshuai@linux.alibaba.com>
Precedence: bulk

On Sun, Jan 16, 2022 at 04:43:10PM +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(). This patch is to reduce the time before GHES
> initialization.
> 
> 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.  For
> example, when the kernel booting, the console logs many times from
> firmware before GHES drivers init in our platform:
> 
> 	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

If I understand correctly, the firmware noticed an error, tried to
report it to the kernel, and is complaining because the kernel isn't
ready to handle it yet.  And the reason for this patch is to reduce
these complaints from the firmware.

That doesn't seem like a very good reason for this patch.  There is
*always* a window before the kernel is ready to handle events from the
firmware.

Why is the firmware noticing these errors in the first place?  If
you're seeing these complaints regularly, my guess is that either you
have some terrible hardware or (more likely) the firmware isn't
clearing some expected error condition correctly.  For example, maybe
the Unsupported Request errors that happen while enumerating PCIe
devices are being reported.

If you register the callback function, the kernel will now start
seeing these error reports.  What happens then?  Does the kernel log
the errors somewhere?  Is that better than the current situation where
the firmware logs them?

However, I DO think that:

  - Removing acpi_hest_init() from acpi_pci_root_init(), and

  - Converting ghes_init() and sdei_init() from initcalls to explicit
    calls

are very good reasons to do something like this patch because HEST is
not PCI-specific, and IMO, explicit calls are better than initcalls
because initcall ordering is implicit and not well-defined within a
level.

> This is because the callback function has not been registered yet.  Due
> to the poor design of firmware, 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.
> 
> 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() => acpi_bus_init() => acpi_init()
> 	ghes_init() => sdei_init()
> 
> Based on above, move sdei_init and ghes_init as far ahead as possible,
> right after acpi_iort_init() in acpi_init(). After this patch, there are
> still errors missing, but we have to tolerate it until the software
> reporting capability is built. And this patch merely reduce the time
> before GHES initialization. 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.
> 
> As we can see, the initialization of GHES is advanced by 33 seconds.
> (It should be noted that the effect of optimization varies with the
> platform.)
> 
> Signed-off-by: Shuai Xue <xueshuai@linux.alibaba.com>
> ---
>  drivers/acpi/apei/ghes.c    | 18 ++++++++----------
>  drivers/acpi/bus.c          |  4 ++++
>  drivers/acpi/pci_root.c     |  4 ++--
>  drivers/firmware/arm_sdei.c | 13 ++-----------
>  include/acpi/apei.h         |  2 ++
>  include/linux/arm_sdei.h    |  2 ++
>  6 files changed, 20 insertions(+), 23 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 0c5c9acc6254..64f24a9f213f 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -1457,27 +1457,26 @@ static struct platform_driver ghes_platform_driver = {
>  	.remove		= ghes_remove,
>  };
>  
> -static int __init ghes_init(void)
> +void __init ghes_init(void)
>  {
>  	int rc;
>  
>  	if (acpi_disabled)
> -		return -ENODEV;
> +		return;
>  
>  	switch (hest_disable) {
>  	case HEST_NOT_FOUND:
> -		return -ENODEV;
> +		pr_info(GHES_PFX "HEST is not found!\n");

I don't know whether this "HEST is not found" message is worthwhile or
not.  I don't think lack of an HEST is an error, and users may be
alarmed.  But this is an ACPI thing, so up to you and Rafael.

> +		return;
>  	case HEST_DISABLED:
>  		pr_info(GHES_PFX "HEST is not enabled!\n");
> -		return -EINVAL;
> +		return;
>  	default:
>  		break;
>  	}
>  
> -	if (ghes_disable) {
> +	if (ghes_disable)
>  		pr_info(GHES_PFX "GHES is not enabled!\n");
> -		return -EINVAL;
> -	}
>  
>  	ghes_nmi_init_cxt();

Previously, if "ghes_disable", we returned immediately.  After this
patch, if "ghes_disable", we print "GHES is not enabled!\n", but then
we go on to call ghes_nmi_init_cxt() and register the
&ghes_platform_driver.  That looks wrong.  Maybe you meant to keep a
"return" here?

> @@ -1495,8 +1494,7 @@ static int __init ghes_init(void)
>  	else
>  		pr_info(GHES_PFX "Failed to enable APEI firmware first mode.\n");
>  
> -	return 0;
> +	return;
>  err:
> -	return rc;
> +	ghes_disable = 1;

Why do you set ghes_disable here?  As far as I can tell, we will never
look at it again.  The places we do look at it are:

  - ghes_init(): earlier in this function, so we've already done that,

  - acpi_hest_init(): we've already called that, too, and

  - acpi_bus_osc_negotiate_platform_control(): called from
    acpi_bus_init(), which we've already called.

>  }
> -device_initcall(ghes_init);
> diff --git a/drivers/acpi/bus.c b/drivers/acpi/bus.c
> index 07f604832fd6..1dcd71df2cd5 100644
> --- a/drivers/acpi/bus.c
> +++ b/drivers/acpi/bus.c
> @@ -30,6 +30,7 @@
>  #include <linux/acpi_viot.h>
>  #include <linux/pci.h>
>  #include <acpi/apei.h>
> +#include <linux/arm_sdei.h>
>  #include <linux/suspend.h>
>  #include <linux/prmt.h>
>  
> @@ -1331,6 +1332,9 @@ static int __init acpi_init(void)
>  
>  	pci_mmcfg_late_init();
>  	acpi_iort_init();
> +	acpi_hest_init();
> +	sdei_init();
> +	ghes_init();

sdei_init() and ghes_init() stick out here because they're the only
functions without an "acpi_" prefix.  Maybe a separate patch to rename
them?

>  	acpi_scan_init();
>  	acpi_ec_init();
>  	acpi_debugfs_init();
> diff --git a/drivers/acpi/pci_root.c b/drivers/acpi/pci_root.c
> index b76db99cced3..14e20af44627 100644
> --- a/drivers/acpi/pci_root.c
> +++ b/drivers/acpi/pci_root.c
> @@ -23,7 +23,7 @@
>  #include <linux/dmi.h>
>  #include <linux/platform_data/x86/apple.h>
>  #include <acpi/apei.h>	/* for acpi_hest_init() */

This #include looks like it may no longer be necessary.

> -
> +#include <linux/arm_sdei.h> /* for sdei_init() */

I don't think this #include is necessary.

>  #include "internal.h"
>  
>  #define ACPI_PCI_ROOT_CLASS		"pci_bridge"
> @@ -943,7 +943,7 @@ struct pci_bus *acpi_pci_root_create(struct acpi_pci_root *root,
>  
>  void __init acpi_pci_root_init(void)
>  {
> -	acpi_hest_init();
> +

Drop the blank line here.

>  	if (acpi_pci_disabled)
>  		return;
>  
> diff --git a/drivers/firmware/arm_sdei.c b/drivers/firmware/arm_sdei.c
> index a7e762c352f9..1e1a51510e83 100644
> --- a/drivers/firmware/arm_sdei.c
> +++ b/drivers/firmware/arm_sdei.c
> @@ -1059,14 +1059,14 @@ static bool __init sdei_present_acpi(void)
>  	return true;
>  }
>  
> -static int __init sdei_init(void)
> +void __init sdei_init(void)
>  {
>  	struct platform_device *pdev;
>  	int ret;
>  
>  	ret = platform_driver_register(&sdei_driver);
>  	if (ret || !sdei_present_acpi())
> -		return ret;
> +		return;
>  
>  	pdev = platform_device_register_simple(sdei_driver.driver.name,
>  					       0, NULL, 0);
> @@ -1076,17 +1076,8 @@ static int __init sdei_init(void)
>  		pr_info("Failed to register ACPI:SDEI platform device %d\n",
>  			ret);
>  	}
> -
> -	return ret;
>  }
>  
> -/*
> - * On an ACPI system SDEI needs to be ready before HEST:GHES tries to register
> - * its events. ACPI is initialised from a subsys_initcall(), GHES is initialised
> - * by device_initcall(). We want to be called in the middle.
> - */
> -subsys_initcall_sync(sdei_init);
> -
>  int sdei_event_handler(struct pt_regs *regs,
>  		       struct sdei_registered_event *arg)
>  {
> diff --git a/include/acpi/apei.h b/include/acpi/apei.h
> index ece0a8af2bae..7dbd6363fda7 100644
> --- a/include/acpi/apei.h
> +++ b/include/acpi/apei.h
> @@ -27,8 +27,10 @@ extern int hest_disable;
>  extern int erst_disable;
>  #ifdef CONFIG_ACPI_APEI_GHES
>  extern bool ghes_disable;
> +void __init ghes_init(void);
>  #else
>  #define ghes_disable 1
> +static inline void ghes_init(void) { return; }

"return" is unnecessary here.

>  #endif
>  
>  #ifdef CONFIG_ACPI_APEI
> diff --git a/include/linux/arm_sdei.h b/include/linux/arm_sdei.h
> index 0a241c5c911d..9c987188b692 100644
> --- a/include/linux/arm_sdei.h
> +++ b/include/linux/arm_sdei.h
> @@ -46,9 +46,11 @@ int sdei_unregister_ghes(struct ghes *ghes);
>  /* For use by arch code when CPU hotplug notifiers are not appropriate. */
>  int sdei_mask_local_cpu(void);
>  int sdei_unmask_local_cpu(void);
> +void __init sdei_init(void);
>  #else
>  static inline int sdei_mask_local_cpu(void) { return 0; }
>  static inline int sdei_unmask_local_cpu(void) { return 0; }
> +static inline void sdei_init(void) { return ; }

"return" is unnecessary here.

>  #endif /* CONFIG_ARM_SDE_INTERFACE */
>  
>  
> -- 
> 2.20.1.12.g72788fdb
> 
> 
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