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From: Thomas Gleixner <tglx@linutronix.de>
To: Vidya Sagar <vidyas@nvidia.com>, bhelgaas@google.com,
 rdunlap@infradead.org, ilpo.jarvinen@linux.intel.com
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
 treding@nvidia.com, jonathanh@nvidia.com, sdonthineni@nvidia.com,
 kthota@nvidia.com, mmaddireddy@nvidia.com, vidyas@nvidia.com,
 sagar.tv@gmail.com, Marc Zyngier <maz@kernel.org>
Subject: Re: [PATCH V2] PCI/MSI: Fix MSI hwirq truncation
In-Reply-To: <20240108120522.1368240-1-vidyas@nvidia.com>
References: <20240105134339.3091497-1-vidyas@nvidia.com>
 <20240108120522.1368240-1-vidyas@nvidia.com>
Date: Wed, 10 Jan 2024 11:12:23 +0100
Message-ID: <87il41jy48.ffs@tglx>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain

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@nvidia.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.

Thanks,

        tglx