linux-kernel - Re: [PATCH V4 01/10] acpi: apei: read ack upon ghes record consumption

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Date:   Mon, 24 Oct 2016 14:28:09 -0600
From:   "Baicar, Tyler" <tbaicar@...eaurora.org>
To:     Suzuki K Poulose <Suzuki.Poulose@....com>, marc.zyngier@....com,
        pbonzini@...hat.com, rkrcmar@...hat.com, linux@...linux.org.uk,
        catalin.marinas@....com, will.deacon@....com, rjw@...ysocki.net,
        lenb@...nel.org, matt@...eblueprint.co.uk, robert.moore@...el.com,
        lv.zheng@...el.com, nkaje@...eaurora.org, zjzhang@...eaurora.org,
        mark.rutland@....com, james.morse@....com,
        akpm@...ux-foundation.org, eun.taik.lee@...sung.com,
        sandeepa.s.prabhu@...il.com, shijie.huang@....com,
        rruigrok@...eaurora.org, paul.gortmaker@...driver.com,
        tomasz.nowicki@...aro.org, fu.wei@...aro.org, rostedt@...dmis.org,
        bristot@...hat.com, linux-arm-kernel@...ts.infradead.org,
        kvmarm@...ts.cs.columbia.edu, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-acpi@...r.kernel.org,
        linux-efi@...r.kernel.org, punit.agrawal@....com,
        astone@...hat.com, harba@...eaurora.org, hanjun.guo@...aro.org
Subject: Re: [PATCH V4 01/10] acpi: apei: read ack upon ghes record
 consumption

On 10/24/2016 2:51 AM, Suzuki K Poulose wrote:
> On 21/10/16 18:30, 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.
>>
>> Signed-off-by: Jonathan (Zhixiong) Zhang <zjzhang@...eaurora.org>
>> Signed-off-by: Richard Ruigrok <rruigrok@...eaurora.org>
>> Signed-off-by: Tyler Baicar <tbaicar@...eaurora.org>
>> Signed-off-by: Naveen Kaje <nkaje@...eaurora.org>
>> ---
>>  drivers/acpi/apei/ghes.c | 42 
>> ++++++++++++++++++++++++++++++++++++++++++
>>  drivers/acpi/apei/hest.c |  7 +++++--
>>  include/acpi/ghes.h      |  5 ++++-
>>  3 files changed, 51 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/acpi/apei/ghes.c b/drivers/acpi/apei/ghes.c
>> index 60746ef..7d020b0 100644
>> --- a/drivers/acpi/apei/ghes.c
>> +++ b/drivers/acpi/apei/ghes.c
>> @@ -45,6 +45,7 @@
>>  #include <linux/aer.h>
>>  #include <linux/nmi.h>
>>
>> +#include <acpi/actbl1.h>
>>  #include <acpi/ghes.h>
>>  #include <acpi/apei.h>
>>  #include <asm/tlbflush.h>
>> @@ -79,6 +80,10 @@
>>      ((struct acpi_hest_generic_status *)                \
>>       ((struct ghes_estatus_node *)(estatus_node) + 1))
>>
>> +#define HEST_TYPE_GENERIC_V2(ghes)                \
>> +    ((struct acpi_hest_header *)ghes->generic)->type ==    \
>> +     ACPI_HEST_TYPE_GENERIC_ERROR_V2
>> +
>>  /*
>>   * This driver isn't really modular, however for the time being,
>>   * continuing to use module_param is the easiest way to remain
>> @@ -248,7 +253,15 @@ 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 (HEST_TYPE_GENERIC_V2(ghes)) {
>> +        rc = apei_map_generic_address(
>> +            &ghes->generic_v2->read_ack_register);
>> +        if (rc)
>> +            goto err_unmap;
>
> I think should be goto err_free, see more below.
>
>> +    }
>> +
>>      rc = apei_map_generic_address(&generic->error_status_address);
>>      if (rc)
>>          goto err_free;
>> @@ -270,6 +283,9 @@ static struct ghes *ghes_new(struct 
>> acpi_hest_generic *generic)
>>
>>  err_unmap:
>> apei_unmap_generic_address(&generic->error_status_address);
>> +    if (HEST_TYPE_GENERIC_V2(ghes))
>> +        apei_unmap_generic_address(
>> +            &ghes->generic_v2->read_ack_register);
>
> We might end up trying to unmap (error_status_address) which is not 
> mapped
> if we hit the error in mapping read_ack_register. The 
> read_ack_register unmap
> hunk should be moved below to err_free.
>
This needs to be changed, I'll add a separate label for unmapping 
read_ack_register and error_status_address for the case that the 
read_ack_register map succeeds but the error_status_address map fails.

err_unmap_status_addr:
apei_unmap_generic_address(&generic->error_status_address);
err_unmap_read_ack_addr:
         if (HEST_TYPE_GENERIC_V2(ghes))
                 apei_unmap_generic_address(
&ghes->generic_v2->read_ack_register);
err_free:
         kfree(ghes);
         return ERR_PTR(rc);

If mapping read_ack_register fails, goto err_free.
If mapping read_ack_register is successful but mapping 
error_status_address fails, goto err_unmap_read_ack_addr.
And if both mappings succeed but the kmalloc fails, then goto 
err_unmap_status_addr.

>
>>  err_free:
>>      kfree(ghes);
>>      return ERR_PTR(rc);
>> @@ -279,6 +295,9 @@ static void ghes_fini(struct ghes *ghes)
>>  {
>>      kfree(ghes->estatus);
>> apei_unmap_generic_address(&ghes->generic->error_status_address);
>> +    if (HEST_TYPE_GENERIC_V2(ghes))
>> +        apei_unmap_generic_address(
>> +            &ghes->generic_v2->read_ack_register);
>>  }
>>
>>  static inline int ghes_severity(int severity)
>> @@ -648,6 +667,23 @@ static void ghes_estatus_cache_add(
>>      rcu_read_unlock();
>>  }
>>
>
>> +static int ghes_do_read_ack(struct acpi_hest_generic_v2 *generic_v2)
>
> nit: We are actually writing something to the read_ack_register. The 
> names
> read_ack_register (which may be as per standard) and more importantly the
> function name (ghes_do_read_ack) sounds a bit misleading.
It is called "Read Ack Register" in the spec (ACPI 6.1 table 18-344), 
but I agree the function name can be improved.
Maybe ghes_acknowledge_error or ghes_ack_error.

Thanks,
Tyler
>
> Rest looks fine to me.
>
> Suzuki
>

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