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Date:   Wed, 14 Jun 2023 11:09:10 -0400
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Cc:     yazen.ghannam@amd.com, linux-kernel@vger.kernel.org,
        tony.luck@intel.com, x86@kernel.org, muralidhara.mk@amd.com,
        joao.m.martins@oracle.com, william.roche@oracle.com,
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        baolin.wang@linux.alibaba.com
Subject: Re: [PATCH 2/3] x86/mce: Define amd_mce_usable_address()
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To:     Shuai Xue <xueshuai@linux.alibaba.com>, linux-edac@vger.kernel.org
References: <20230613141142.36801-1-yazen.ghannam@amd.com>
 <20230613141142.36801-3-yazen.ghannam@amd.com>
 <31fdaacc-cc2b-5ea5-8a0e-e5ccfe674834@linux.alibaba.com>
From:   Yazen Ghannam <yazen.ghannam@amd.com>
In-Reply-To: <31fdaacc-cc2b-5ea5-8a0e-e5ccfe674834@linux.alibaba.com>
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On 6/13/2023 10:19 PM, Shuai Xue wrote:
> 
> 
> On 2023/6/13 22:11, Yazen Ghannam wrote:
>> Currently, all valid MCA_ADDR values are assumed to be usable on AMD
>> systems. However, this is not correct in most cases. Notifiers expecting
>> usable addresses may then operate on inappropriate values.
>>
>> Define a helper function to do AMD-specific checks for a usable memory
>> address. List out all known cases.
>>
>> Signed-off-by: Yazen Ghannam <yazen.ghannam@amd.com>
>> ---
>>   arch/x86/kernel/cpu/mce/amd.c      | 38 ++++++++++++++++++++++++++++++
>>   arch/x86/kernel/cpu/mce/core.c     |  3 +++
>>   arch/x86/kernel/cpu/mce/internal.h |  2 ++
>>   3 files changed, 43 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/mce/amd.c b/arch/x86/kernel/cpu/mce/amd.c
>> index 1ccfb0c9257f..ca79fa10b844 100644
>> --- a/arch/x86/kernel/cpu/mce/amd.c
>> +++ b/arch/x86/kernel/cpu/mce/amd.c
>> @@ -746,6 +746,44 @@ bool amd_mce_is_memory_error(struct mce *m)
>>   	return legacy_mce_is_memory_error(m);
>>   }
>>   
>> +/*
>> + * AMD systems do not have an explicit indicator that the value in MCA_ADDR is
>> + * a system physical address. Therefore individual cases need to be detected.
>> + * Future cases and checks will be added as needed.
>> + *
>> + * 1) General case
>> + *	a) Assume address is not usable.
>> + * 2) "Poison" errors
>> + *	a) Indicated by MCA_STATUS[43]: POISON. Defined for all banks except legacy
>> + *	   Northbridge (bank 4).
>> + *	b) Refers to poison consumption in the Core. Does not include "no action",
>> + *	   "action optional", or "deferred" error severities.
>> + *	c) Will include a usuable address so that immediate action can be taken.
>> + * 3) Northbridge DRAM ECC errors
>> + *	a) Reported in legacy bank 4 with XEC 8.
>> + *	b) MCA_STATUS[43] is *not* defined as POISON in legacy bank 4. Therefore,
>> + *	   this bit should not be checked.
> [nit]
> 
>> + *
>> + * NOTE: SMCA UMC memory errors fall into case #1.
> 
> hi, Yazen
> 
> The address for SMCA UMC memory error is not system physical address, it make sense
> to be not usable. But how we deal with the SMCA address? The MCE chain like
> uc_decode_notifier will do a sanity check with mce_usable_address and it will not
> handle SMCA address.
>

Hi Shuai,

That's correct.

There isn't a good solution today. This will be handled in future changes.

Thanks,
Yazen