linux-kernel - Re: [PATCH 1/5] x86/mce/inject: Check if a bank is unpopulated before error simulation

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Date:   Mon, 27 Sep 2021 14:51:56 -0500
From:   Smita Koralahalli Channabasappa <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 1/5] x86/mce/inject: Check if a bank is unpopulated before
 error simulation

Hi Boris,

On 9/24/21 3:26 AM, Borislav Petkov wrote:

> On Wed, Sep 15, 2021 at 06:27:35PM -0500, Smita Koralahalli wrote:
>> The MCA_IPID register uniquely identifies a bank's type on Scalable MCA
>> (SMCA) systems. When an MCA bank is not populated, the MCA_IPID register
>> will read as zero and writes to it will be ignored. Check the value of
>> this register before trying to simulate the error.
>>
>> Signed-off-by: Smita Koralahalli <Smita.KoralahalliChannabasappa@....com>
>> ---
>>   arch/x86/kernel/cpu/mce/inject.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/arch/x86/kernel/cpu/mce/inject.c b/arch/x86/kernel/cpu/mce/inject.c
>> index 0bfc14041bbb..51ac575c4605 100644
>> --- a/arch/x86/kernel/cpu/mce/inject.c
>> +++ b/arch/x86/kernel/cpu/mce/inject.c
>> @@ -577,6 +577,24 @@ static int inj_bank_set(void *data, u64 val)
>>   	}
>>
>> +	if (boot_cpu_has(X86_FEATURE_SMCA)) {
> This whole thing belongs into inj_ipid_set() where you should verify
> whether the bank is set when you try to set the IPID for that bank.

Can you please elaborate on this? I'm not sure if I understood this
right. Should I read the ipid file to verify that the user has input
proper ipid? If ipid file reads zero then do rdmsrl_on_cpu?

Thanks,
Smita

>
> +			if (!m->ipid) {
> +				pr_err("Error simulation not possible: Bank %llu unpopulated\n",
>> +
>> +		/* Check for user provided IPID value. */
>> +		if (!m->ipid) {
>> +			rdmsrl_on_cpu(m->extcpu, MSR_AMD64_SMCA_MCx_IPID(val),
>> +				      &m->ipid);
> Oh well, one IPI per ipid write. We're doing injection so we can't be on
> a production machine so who cares about IPIs there.
>