linux-kernel - Re: [PATCH V2] PCI/MSI: Fix MSI hwirq truncation

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Date: Wed, 10 Jan 2024 23:34:44 +0530
From: Vidya Sagar <vidyas@...dia.com>
To: Thomas Gleixner <tglx@...utronix.de>, bhelgaas@...gle.com,
 rdunlap@...radead.org, ilpo.jarvinen@...ux.intel.com
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,
 Marc Zyngier <maz@...nel.org>
Subject: Re: [PATCH V2] PCI/MSI: Fix MSI hwirq truncation



On 1/10/2024 3:42 PM, Thomas Gleixner wrote:
> External email: Use caution opening links or attachments
> 
> 
> On Mon, Jan 08 2024 at 17:35, 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 u32. 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 u64 before left shifting it to
>> calculate hwirq number.
>>
>> Fixes: 3878eaefb89a ("PCI/MSI: Enhance core to support hierarchy irqdomain")
>> Signed-off-by: Vidya Sagar <vidyas@...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;
> 
> This is not casting to u64. It's casting to unsigned long:
> 
>    typedef unsigned long irq_hw_number_t;
> 
> So this works only correctly on 64bit. On 32bit kernels unsigned long is
> still 32bit. It's probably arguable that the 32bit case is not a
> problem, but the changelog and the change do not match. This needs a
> proper explanation why we don't care about this on 32bit.
Agree that the change and the commit message do not match.
I'll update the commit message to use 'irq_hw_number_t' instead of u64.

Thanks,
Vidya Sagar

> 
> Thanks,
> 
>          tglx