linux-kernel - Re: [PATCH v2 2/5] x86/mce/inject: Warn the user on a not set valid bit in MCA

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Message-ID: <00f4a0ab-f241-6674-f37f-623f3d9a8337@amd.com>
Date:   Tue, 26 Oct 2021 11:58:58 -0500
From:   "Koralahalli Channabasappa, Smita" <skoralah@....com>
To:     Borislav Petkov <bp@...en8.de>,
        Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
Cc:     x86@...nel.org, linux-edac@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tony Luck <tony.luck@...el.com>,
        "H . Peter Anvin" <hpa@...or.com>, yazen.ghannam@....com
Subject: Re: [PATCH v2 2/5] x86/mce/inject: Warn the user on a not set valid
 bit in MCA_STATUS

Hi Boris,

On 10/26/21 5:02 AM, Borislav Petkov wrote:

> On Tue, Oct 19, 2021 at 06:36:38PM -0500, Smita Koralahalli wrote:
>> MCA handlers check the valid bit in each status register (MCA_STATUS[Val])
>> and will likely ignore signatures if the valid bit is not set.
>>
>> Warn the user if the valid bit is not set before doing error injection.
>>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
>> ---
>> v2:
>> 	Added a warning statement instead of setting the valid bit.
>> ---
>>   arch/x86/kernel/cpu/mce/inject.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
>> index 601efd104bb4..a993dc3d0333 100644
>> --- a/arch/x86/kernel/cpu/mce/inject.c
>> +++ b/arch/x86/kernel/cpu/mce/inject.c
>> @@ -487,6 +487,9 @@ static void do_inject(void)
>>   
>>   	i_mce.tsc = rdtsc_ordered();
>>   
>> +	if (!(i_mce.status & MCI_STATUS_VAL))
>> +		pr_warn("Handlers might ignore signatures with Val=0 in MCA_STATUS\n");
>> +
>>   	if (i_mce.misc)
>>   		i_mce.status |= MCI_STATUS_MISCV;
>>   
>> -- 
> So what's the real reason for this?
>
> You've injected and you didn't get any feedback and were wondering why?
>
> If handlers ignore !VAL MCEs, why don't you simply set it
> unconditionally on entry to do_inject()?

Like how it was done here?
https://lkml.kernel.org/r/20210915232739.6367-3-Smita.KoralahalliChannabasappa@amd.com

Thanks,