linux-kernel - Re: [PATCH v3] s390/pci: fix CPU address in MSI for directed IRQ

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Date:   Fri, 27 Nov 2020 11:08:10 +0100
From:   Niklas Schnelle <schnelle@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>,
        Alexander Gordeev <agordeev@...ux.ibm.com>
Cc:     linux-s390@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] s390/pci: fix CPU address in MSI for directed IRQ



On 11/27/20 9:56 AM, Halil Pasic wrote:
> On Thu, 26 Nov 2020 18:00:37 +0100
> Alexander Gordeev <agordeev@...ux.ibm.com> wrote:
> 
>> The directed MSIs are delivered to CPUs whose address is
>> written to the MSI message data. The current code assumes
>> that a CPU logical number (as it is seen by the kernel)
>> is also that CPU address.
>>
>> The above assumption is not correct, as the CPU address
>> is rather the value returned by STAP instruction. That
>> value does not necessarily match the kernel logical CPU
>> number.
>>
>> Fixes: e979ce7bced2 ("s390/pci: provide support for CPU directed interrupts")
>> Signed-off-by: Alexander Gordeev <agordeev@...ux.ibm.com>
>> ---
>>  arch/s390/pci/pci_irq.c | 14 +++++++++++---
>>  1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/arch/s390/pci/pci_irq.c b/arch/s390/pci/pci_irq.c
>> index 743f257cf2cb..75217fb63d7b 100644
>> --- a/arch/s390/pci/pci_irq.c
>> +++ b/arch/s390/pci/pci_irq.c
>> @@ -103,9 +103,10 @@ static int zpci_set_irq_affinity(struct irq_data *data, const struct cpumask *de
>>  {
>>  	struct msi_desc *entry = irq_get_msi_desc(data->irq);
>>  	struct msi_msg msg = entry->msg;
>> +	int cpu_addr = smp_cpu_get_cpu_address(cpumask_first(dest));
>>  
>>  	msg.address_lo &= 0xff0000ff;
>> -	msg.address_lo |= (cpumask_first(dest) << 8);
>> +	msg.address_lo |= (cpu_addr << 8);
>>  	pci_write_msi_msg(data->irq, &msg);
>>  
>>  	return IRQ_SET_MASK_OK;
>> @@ -238,6 +239,7 @@ int arch_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
>>  	unsigned long bit;
>>  	struct msi_desc *msi;
>>  	struct msi_msg msg;
>> +	int cpu_addr;
>>  	int rc, irq;
>>  
>>  	zdev->aisb = -1UL;
>> @@ -287,9 +289,15 @@ int arch_setup_msi_irqs(struct pci_dev *pdev, int nvec, int type)
>>  					 handle_percpu_irq);
>>  		msg.data = hwirq - bit;
>>  		if (irq_delivery == DIRECTED) {
>> +			if (msi->affinity)
>> +				cpu = cpumask_first(&msi->affinity->mask);
>> +			else
>> +				cpu = 0;
>> +			cpu_addr = smp_cpu_get_cpu_address(cpu);
>> +
> 
> I thin style wise, I would prefer keeping the ternary operator instead
> of rewriting it as an if-then-else, i.e.:
>                         cpu_addr = smp_cpu_get_cpu_address(msi->affinity ?      
>                                 cpumask_first(&msi->affinity->mask) : 0);
> but either way:
> 
> Reviewed-by: Halil Pasic <pasic@...ux.ibm.com> 

Thanks for your review, lets keep the if/else its certainly not less
readable even if it may be less pretty.

Found another thing (not directly in the touched code) but I'm now
wondering about. In zpci_handle_cpu_local_irq()
we do
	struct airq_iv *dibv = zpci_ibv[smp_processor_id()];

does that also need to use some _address() variant? If it does that
then dicatates that the CPU addresses must start at 0.

> 
>>  			msg.address_lo = zdev->msi_addr & 0xff0000ff;
>> -			msg.address_lo |= msi->affinity ?
>> -				(cpumask_first(&msi->affinity->mask) << 8) : 0;
>> +			msg.address_lo |= (cpu_addr << 8);
>> +
>>  			for_each_possible_cpu(cpu) {
>>  				airq_iv_set_data(zpci_ibv[cpu], hwirq, irq);
>>  			}
>