Re: [PATCH v2] x86/mce: retrieve poison range from hardware whenever supported

[Jane Chu]

On 7/15/2022 9:50 PM, Dan Williams wrote:
> Jane Chu wrote:
>> With Commit 7917f9cdb503 ("acpi/nfit: rely on mce->misc to determine
>> poison granularity") that changed nfit_handle_mce() callback to report
>> badrange according to 1ULL << MCI_MISC_ADDR_LSB(mce->misc), it's been
>> discovered that the mce->misc LSB field is 0x1000 bytes, hence injecting
>> 2 back-to-back poisons and the driver ends up logging 8 badblocks,
>> because 0x1000 bytes is 8 512-byte.
>>
>> Dan Williams noticed that apei_mce_report_mem_error() hardcode
>> the LSB field to PAGE_SHIFT instead of consulting the input
>> struct cper_sec_mem_err record.  So change to rely on hardware whenever
>> support is available.
>>
>> v1: https://lkml.org/lkml/2022/7/15/1040
> 
> This should be "Link:" and it should reference lore.kernel.org by
> msg-id. Lore is maintained by LF infrastructure and the message-id can
> be used to search lore.kernel.org mirrors even if the LF infra is down.
> 
> Link: https://lore.kernel.org/r/7ed50fd8-521e-cade-77b1-738b8bfb8502@xxxxxxxxxx
> 

Got it, thanks!

>> Signed-off-by: Jane Chu <jane.chu@xxxxxxxxxx>
>> ---
>>   arch/x86/kernel/cpu/mce/apei.c | 6 +++++-
>>   1 file changed, 5 insertions(+), 1 deletion(-)
>>
>> diff --git a/arch/x86/kernel/cpu/mce/apei.c b/arch/x86/kernel/cpu/mce/apei.c
>> index 717192915f28..a4d5893632e0 100644
>> --- a/arch/x86/kernel/cpu/mce/apei.c
>> +++ b/arch/x86/kernel/cpu/mce/apei.c
>> @@ -29,6 +29,7 @@
>>   void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
>>   {
>>   	struct mce m;
>> +	int lsb;
>>   
>>   	if (!(mem_err->validation_bits & CPER_MEM_VALID_PA))
>>   		return;
>> @@ -37,7 +38,10 @@ void apei_mce_report_mem_error(int severity, struct cper_sec_mem_err *mem_err)
>>   	m.bank = -1;
>>   	/* Fake a memory read error with unknown channel */
>>   	m.status = MCI_STATUS_VAL | MCI_STATUS_EN | MCI_STATUS_ADDRV | MCI_STATUS_MISCV | 0x9f;
>> -	m.misc = (MCI_MISC_ADDR_PHYS << 6) | PAGE_SHIFT;
>> +	lsb = __builtin_ffs(mem_err->physical_addr_mask) - 1;
> 
> Just use the kernel's __ffs64() which does not require the substraction

Will do.

> fixup, and you can assume that physical_address_mask is non-zero just
> like trace_extlog_mem_event() does.

I guess to me, a more convincing evidence is
         /* Error grain */
         if (mem_err->validation_bits & CPER_MEM_VALID_PA_MASK)
                 e->grain = ~mem_err->physical_addr_mask + 1;
in ghes_edac_report_mem_error().

> 
>> +	if (lsb <= 0)
>> +		lsb = PAGE_SHIFT;
> 
> This fixup can then be removed as well.
> 
> After the above comments are addressed you can add:
> 
> Reviewed-by: Dan Williams <dan.j.williams@xxxxxxxxx>

Thanks!
-jane