linux-kernel - Re: [PATCH v6 3/4] x86/mce: Handle AMD threshold interrupt storms

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Date:   Fri, 23 Jun 2023 11:54:35 -0400
From:   Yazen Ghannam <yazen.ghannam@....com>
To:     Borislav Petkov <bp@...en8.de>,
        Smita.KoralahalliChannabasappa@....com
Cc:     yazen.ghannam@....com, Tony Luck <tony.luck@...el.com>,
        dave.hansen@...ux.intel.com, x86@...nel.org,
        linux-edac@...r.kernel.org, linux-kernel@...r.kernel.org,
        patches@...ts.linux.dev
Subject: Re: [PATCH v6 3/4] x86/mce: Handle AMD threshold interrupt storms

On 6/23/2023 10:45 AM, Borislav Petkov wrote:
> On Fri, Jun 16, 2023 at 11:27:43AM -0700, Tony Luck wrote:
>> +static void _reset_block(struct threshold_block *block)
>> +{
>> +	struct thresh_restart tr;
>> +
>> +	memset(&tr, 0, sizeof(tr));
>> +	tr.b = block;
>> +	threshold_restart_bank(&tr);
>> +}
> 
>> +
>> +static void toggle_interrupt_reset_block(struct threshold_block *block, bool on)
>> +{
>> +	if (!block)
>> +		return;
>> +
>> +	block->interrupt_enable = !!on;
>> +	_reset_block(block);
>> +}
>> +
>> +void mce_amd_handle_storm(int bank, bool on)
>> +{
>> +	struct threshold_block *first_block = NULL, *block = NULL, *tmp = NULL;
>> +	struct threshold_bank **bp = this_cpu_read(threshold_banks);
>> +	unsigned long flags;
>> +
>> +	if (!bp)
>> +		return;
>> +
>> +	local_irq_save(flags);
>> +
>> +	first_block = bp[bank]->blocks;
>> +	if (!first_block)
>> +		goto end;
>> +
>> +	toggle_interrupt_reset_block(first_block, on);
>> +
>> +	list_for_each_entry_safe(block, tmp, &first_block->miscj, miscj)
>> +		toggle_interrupt_reset_block(block, on);
>> +end:
>> +	local_irq_restore(flags);
>> +}
> 
> There's already other code which does this threshold block control. Pls
> refactor and unify it instead of adding almost redundant similar functions.
>

Okay, will do.

>>   static void mce_threshold_block_init(struct threshold_block *b, int offset)
>>   {
>>   	struct thresh_restart tr = {
>> @@ -868,6 +909,7 @@ static void amd_threshold_interrupt(void)
>>   	struct threshold_block *first_block = NULL, *block = NULL, *tmp = NULL;
>>   	struct threshold_bank **bp = this_cpu_read(threshold_banks);
>>   	unsigned int bank, cpu = smp_processor_id();
>> +	u64 status;
>>   
>>   	/*
>>   	 * Validate that the threshold bank has been initialized already. The
>> @@ -881,6 +923,13 @@ static void amd_threshold_interrupt(void)
>>   		if (!(per_cpu(bank_map, cpu) & BIT_ULL(bank)))
>>   			continue;
>>   
>> +		rdmsrl(mca_msr_reg(bank, MCA_STATUS), status);
>> +		track_cmci_storm(bank, status);
> 
> So this is called from interrupt context.
> 
> There's another track_cmci_storm() from machine_check_poll() which can
> happen in process context.
> 
> And there's no sync (locking) between the two. Not good.
> 
> Why are even two calls needed on AMD?
> 

I think because the AMD interrupt handlers don't call 
machine_check_poll(). This is a good opportunity to unify the AMD 
thresholding and deferred error interrupt handlers with 
machine_check_poll().

Tony,
Please leave out this AMD patch for now. I'll work on refactoring it.

Thanks,
Yazen