linux-kernel - Re: [PATCH V4] PCI/MSI: Fix MSI hwirq truncation

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Date: Wed, 31 Jan 2024 08:45:58 +0530
From: Vidya Sagar <vidyas@...dia.com>
To: bhelgaas@...gle.com, rdunlap@...radead.org,
 ilpo.jarvinen@...ux.intel.com, tglx@...utronix.de
Cc: linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
 treding@...dia.com, jonathanh@...dia.com, sdonthineni@...dia.com,
 kthota@...dia.com, mmaddireddy@...dia.com, sagar.tv@...il.com
Subject: Re: [PATCH V4] PCI/MSI: Fix MSI hwirq truncation

Hi Thomas,
Sorry to bother you.
Would you mind giving an Ack to this patch?

Thanks,
Vidya Sagar

On 1/23/2024 9:31 PM, Vidya Sagar wrote:
> Hi Thomas,
> Does this patch look fine to you?
> If yes, would you mind giving an Ack?
> 
> Thanks,
> Vidya Sagar
> 
> On 1/15/2024 7:26 PM, Vidya Sagar wrote:
>> While calculating the hwirq number for an MSI interrupt, the higher
>> bits (i.e. from bit-5 onwards a.k.a domain_nr >= 32) of the PCI domain
>> number gets truncated because of the shifted value casting to return
>> type of pci_domain_nr() which is 'int'. This for example is resulting
>> in same hwirq number for devices 0019:00:00.0 and 0039:00:00.0.
>>
>> So, cast the PCI domain number to 'irq_hw_number_t' before left shifting
>> it to calculate hwirq number. Please note that this fixes the issue only
>> on 64-bit systems and doesn't change the behavior in 32-bit systems i.e.
>> the 32-bit systems continue to have the issue. Since the issue surfaces
>> only if there are too many PCIe controllers in the system which usually
>> is the case in modern server systems and they don't tend to run 32-bit
>> kernels.
>>
>> Fixes: 3878eaefb89a ("PCI/MSI: Enhance core to support hierarchy 
>> irqdomain")
>> Tested-by: Shanker Donthineni <sdonthineni@...dia.com>
>> Signed-off-by: Vidya Sagar <vidyas@...dia.com>
>> ---
>> V4:
>> * Added extra information in the change log about the impact of this 
>> patch
>>    in a 32-bit system as suggested by Thomas
>>
>> V3:
>> * Addressed review comments from Thomas Gleixner
>> * Added Tested-By: Shanker Donthineni <sdonthineni@...dia.com>
>>
>> V2:
>> * Added Fixes tag
>>
>>   drivers/pci/msi/irqdomain.c | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
>> index c8be056c248d..cfd84a899c82 100644
>> --- a/drivers/pci/msi/irqdomain.c
>> +++ b/drivers/pci/msi/irqdomain.c
>> @@ -61,7 +61,7 @@ static irq_hw_number_t 
>> pci_msi_domain_calc_hwirq(struct msi_desc *desc)
>>       return (irq_hw_number_t)desc->msi_index |
>>           pci_dev_id(dev) << 11 |
>> -        (pci_domain_nr(dev->bus) & 0xFFFFFFFF) << 27;
>> +        ((irq_hw_number_t)(pci_domain_nr(dev->bus) & 0xFFFFFFFF)) << 27;
>>   }
>>   static void pci_msi_domain_set_desc(msi_alloc_info_t *arg,