Re: [PATCH V15 01/11] acpi: apei: read ack upon ghes record consumption

[Borislav Petkov <bp@alien8.de>]

On Tue, Apr 18, 2017 at 05:05:13PM -0600, Tyler Baicar wrote:
> A RAS (Reliability, Availability, Serviceability) controller
> may be a separate processor running in parallel with OS
> execution, and may generate error records for consumption by
> the OS. If the RAS controller produces multiple error records,
> then they may be overwritten before the OS has consumed them.
> 
> The Generic Hardware Error Source (GHES) v2 structure
> introduces the capability for the OS to acknowledge the
> consumption of the error record generated by the RAS
> controller. A RAS controller supporting GHESv2 shall wait for
> the acknowledgment before writing a new error record, thus
> eliminating the race condition.
> 
> Add support for parsing of GHESv2 sub-tables as well.
> 
> Signed-off-by: Tyler Baicar <tbaicar@codeaurora.org>
> CC: Jonathan (Zhixiong) Zhang <zjzhang@codeaurora.org>
> Reviewed-by: James Morse <james.morse@arm.com>
> ---
>  drivers/acpi/apei/ghes.c | 55 +++++++++++++++++++++++++++++++++++++++++++++---
>  drivers/acpi/apei/hest.c |  7 ++++--
>  include/acpi/ghes.h      |  5 ++++-
>  3 files changed, 61 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
> index 79b3c9c..6d87ab7 100644
> --- a/drivers/acpi/apei/ghes.c
> +++ b/drivers/acpi/apei/ghes.c
> @@ -46,6 +46,7 @@
>  #include <linux/nmi.h>
>  #include <linux/sched/clock.h>
>  
> +#include <acpi/actbl1.h>
>  #include <acpi/ghes.h>
>  #include <acpi/apei.h>
>  #include <asm/tlbflush.h>
> @@ -80,6 +81,10 @@
>  	((struct acpi_hest_generic_status *)				\
>  	 ((struct ghes_estatus_node *)(estatus_node) + 1))
>  
> +#define IS_HEST_TYPE_GENERIC_V2(ghes)				\
> +	((struct acpi_hest_header *)ghes->generic)->type ==	\

This is a nasty hack: casting the ghes->generic pointer to a pointer of its
first member which is a acpi_hest_header.

Why isn't this a nice inline function with proper dereferencing:

static inline bool is_hest_type_generic_v2(struct ghes *ghes)
{
        return ghes->generic->header.type == ACPI_HEST_TYPE_GENERIC_ERROR_V2;
}

?

Also, please integrate scripts/checkpatch.pl in your patch creation
workflow. Some of the warnings/errors *actually* make sense.

>  /*
>   * This driver isn't really modular, however for the time being,
>   * continuing to use module_param is the easiest way to remain
> @@ -240,6 +245,17 @@ static int ghes_estatus_pool_expand(unsigned long len)
>  	return 0;
>  }
>  
> +static int map_gen_v2(struct ghes *ghes)
> +{
> +	return apei_map_generic_address(&ghes->generic_v2->read_ack_register);
> +}
> +
> +static void unmap_gen_v2(struct ghes *ghes)
> +{
> +	apei_unmap_generic_address(&ghes->generic_v2->read_ack_register);
> +	return;
> +}

Like this one, for example:

WARNING: void function return statements are not generally useful
#89: FILE: drivers/acpi/apei/ghes.c:257:
+       return;
+}

> +
>  static struct ghes *ghes_new(struct acpi_hest_generic *generic)
>  {
>  	struct ghes *ghes;
> @@ -249,10 +265,17 @@ static struct ghes *ghes_new(struct acpi_hest_generic *generic)
>  	ghes = kzalloc(sizeof(*ghes), GFP_KERNEL);
>  	if (!ghes)
>  		return ERR_PTR(-ENOMEM);
> +
>  	ghes->generic = generic;
> +	if (IS_HEST_TYPE_GENERIC_V2(ghes)) {
> +		rc = map_gen_v2(ghes);
> +		if (rc)
> +			goto err_free;
> +	}
> +
>  	rc = apei_map_generic_address(&generic->error_status_address);
>  	if (rc)
> -		goto err_free;
> +		goto err_unmap_read_ack_addr;
>  	error_block_length = generic->error_block_length;
>  	if (error_block_length > GHES_ESTATUS_MAX_SIZE) {
>  		pr_warning(FW_WARN GHES_PFX
> @@ -264,13 +287,16 @@ static struct ghes *ghes_new(struct acpi_hest_generic *generic)
>  	ghes->estatus = kmalloc(error_block_length, GFP_KERNEL);
>  	if (!ghes->estatus) {
>  		rc = -ENOMEM;
> -		goto err_unmap;
> +		goto err_unmap_status_addr;
>  	}
>  
>  	return ghes;
>  
> -err_unmap:
> +err_unmap_status_addr:
>  	apei_unmap_generic_address(&generic->error_status_address);
> +err_unmap_read_ack_addr:
> +	if (IS_HEST_TYPE_GENERIC_V2(ghes))
> +		unmap_gen_v2(ghes);
>  err_free:
>  	kfree(ghes);
>  	return ERR_PTR(rc);
> @@ -280,6 +306,8 @@ static void ghes_fini(struct ghes *ghes)
>  {
>  	kfree(ghes->estatus);
>  	apei_unmap_generic_address(&ghes->generic->error_status_address);
> +	if (IS_HEST_TYPE_GENERIC_V2(ghes))
> +		unmap_gen_v2(ghes);
>  }
>  
>  static inline int ghes_severity(int severity)
> @@ -649,6 +677,21 @@ static void ghes_estatus_cache_add(
>  	rcu_read_unlock();
>  }
>  
> +static int ghes_ack_error(struct acpi_hest_generic_v2 *generic_v2)

If you name this function parameter to something shorter, say gv2, for
example...

> +{
> +	int rc;
> +	u64 val = 0;
> +
> +	rc = apei_read(&val, &generic_v2->read_ack_register);
> +	if (rc)
> +		return rc;
> +
> +	val &= generic_v2->read_ack_preserve << generic_v2->read_ack_register.bit_offset;
> +	val |= generic_v2->read_ack_write << generic_v2->read_ack_register.bit_offset;

... you can align those two nicely while remaining within the 80 cols width:

        val &= gv2->read_ack_preserve << gv2->read_ack_register.bit_offset;
        val |= gv2->read_ack_write    << gv2->read_ack_register.bit_offset;

and make them readable at a quick glance.

> +
> +	return apei_write(val, &generic_v2->read_ack_register);
> +}
> +
>  static int ghes_proc(struct ghes *ghes)
>  {
>  	int rc;
> @@ -661,6 +704,12 @@ static int ghes_proc(struct ghes *ghes)
>  			ghes_estatus_cache_add(ghes->generic, ghes->estatus);
>  	}
>  	ghes_do_proc(ghes, ghes->estatus);

This needs a comment why v2 needs to ACK the error. The commit message
is not necessarily something we'll find quickly in the future.

> +
> +	if (IS_HEST_TYPE_GENERIC_V2(ghes)) {
> +		rc = ghes_ack_error(ghes->generic_v2);
> +		if (rc)
> +			return rc;
> +	}
>  out:
>  	ghes_clear_estatus(ghes);
>  	return rc;

-- 
Regards/Gruss,
    Boris.

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