Re: [PATCH v3 4/8] acpi/ghes: Extend acpi_ghes_memory_errors() to support multiple CPERs

[Gavin Shan <gshan@redhat.com>]

Hi Jonathan,

On 11/11/25 8:07 PM, Jonathan Cameron wrote:
> On Tue, 11 Nov 2025 14:08:13 +1000
> Gavin Shan <gshan@redhat.com> wrote:
>> On 11/11/25 12:49 AM, Igor Mammedov wrote:
>>> On Thu, 6 Nov 2025 13:15:52 +1000
>>> Gavin Shan <gshan@redhat.com> wrote:
>>>> On 11/6/25 12:14 AM, Jonathan Cameron wrote:
>>>>> On Wed,  5 Nov 2025 21:44:49 +1000
>>>>> Gavin Shan <gshan@redhat.com> wrote:
>>>>>       
>>>>>> In the situation where host and guest has 64KiB and 4KiB page sizes,
>>>>>> one problematic host page affects 16 guest pages. we need to send 16
>>>>>> consective errors in this specific case.
>>>>>>
>>>>>> Extend acpi_ghes_memory_errors() to support multiple CPERs after the
>>>>>> hunk of code to generate the GHES error status is pulled out from
>>>>>> ghes_gen_err_data_uncorrectable_recoverable(). The status field of
>>>>>> generic error status block is also updated accordingly if multiple
>>>>>> error data entries are contained in the generic error status block.
>>>>>>
>>>>>> Signed-off-by: Gavin Shan <gshan@redhat.com>
>>>>> Hi Gavin,
>>>>>
>>>>> Mostly fine, but a few comments on the defines added and a
>>>>> question on what the multiple things are meant to mean?
>>>>>       
>>>>
>>>> Thanks for your review and comments, replies as below.
>>>>   
>>>>>> diff --git a/hw/acpi/ghes.c b/hw/acpi/ghes.c
>>>>>> index a9c08e73c0..527b85c8d8 100644
>>>>>> --- a/hw/acpi/ghes.c
>>>>>> +++ b/hw/acpi/ghes.c
>>>>>> @@ -57,8 +57,12 @@
>>>>>>     /* The memory section CPER size, UEFI 2.6: N.2.5 Memory Error Section */
>>>>>>     #define ACPI_GHES_MEM_CPER_LENGTH           80
>>>>>>     
>>>>>> -/* Masks for block_status flags */
>>>>>> -#define ACPI_GEBS_UNCORRECTABLE         1
>>>>>> +/* Bits for block_status flags */
>>>>>> +#define ACPI_GEBS_UNCORRECTABLE           0
>>>>>> +#define ACPI_GEBS_CORRECTABLE             1
>>>>>> +#define ACPI_GEBS_MULTIPLE_UNCORRECTABLE  2
>>>>>> +#define ACPI_GEBS_MULTIPLE_CORRECTABLE    3
>>>>>
>>>>> So this maps to the bits in block status.
>>>>>
>>>>> I'm not actually sure what these multiple variants are meant to tell us.
>>>>> The multiple error blocks example referred to by the spec is a way to represent
>>>>> the same error applying to multiple places.  So that's one error, many blocks.
>>>>> I have no idea if we set these bits in that case.
>>>>>
>>>>> Based on a quick look I don't think linux even takes any notice.  THere
>>>>> are defines in actbl1.h but I'm not seeing any use made of them.
>>>>>       
>>>>
>>>> I hope Igor can confirm since it was suggested by him.
>>>>
>>>> It's hard to understand how exactly these multiple variants are used from the
>>>> spec. In ACPI 6.5 Table 18.11, it's explained as below.
>>>>
>>>> Bit [2] - Multiple Uncorrectable Errors: If set to one, indicates that more
>>>> than one uncorrectable errors have been detected.
>>>>
>>>> I don't see those multiple variants have been used by Linux. So I think it's
>>>> safe to drop them.
>>>
>>> even though example describes 'same' error at different components,
>>> the bit fields descriptions doesn't set any limits on what 'more than one' means.
>>>
>>> Also from guest POV it's multiple different pages that we are reporting here
>>> as multiple CPERs.
>>> It seems to me that setting *_MULTIPLE_* here is correct thing to do.
>>>    
>>
>> I don't have strong opinions. Lets keep to set _MULTIPLE_ flag if Jonathan
>> is fine. Again, this field isn't used by Linux guest.
> I don't care strongly.  Maybe we should ask for a spec clarification as I doubt
> implementations will be consistent on this given the vague description and that
> Linux ignores it today.
> 

Google Gemini has the following question. If it can be trusted, it should be
set when @num_of_addresses is larger than 1.

Quota from Google Gemini:

The system firmware sets this bit to indicate to the Operating System Power Management (OSPM)
that more than one correctable error condition has been detected and logged for the associated
hardware component since the last time the status was cleared by the software. This is crucial
because a high frequency of correctable errors often indicates a potential underlying hardware
issue that could lead to uncorrectable (and potentially fatal) errors if not addressed (e.g.,
in memory, where multiple correctable errors might trigger a spare memory operation).

>>
>>>>>> +#define ACPI_GEBS_ERROR_DATA_ENTRIES      4
>>>>>
>>>>> This is bits 4-13 and the define isn't used. I'd drop it.
>>>>>       
>>>>
>>>> The definition is used in acpi_ghes_memory_errors() of this patch. However,
>>>> I don't see it has been used by Linux. This field isn't used by Linux to determine
>>>> the total number of error entries. So I think I can drop it either if Igor is ok.
>>>>   
>>
>> Lets keep this field either in next revision if Jonathan is fine.
> 
> I'm fine with the field, but not the value.  As far as I can tell form the spec, it should
> be a mask, not a single bit.
> 

Agreed, lets keep ACPI_HEST_ERROR_ENTRY_COUNT as zero in next revision.

Thanks,
Gavin