linux-kernel - Re: [PATCH] PCI/MSI: Initialize the prepare descriptor by default

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Message-ID: <20250708100248.GA27472@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
Date: Tue, 8 Jul 2025 03:02:48 -0700
From: Shradha Gupta <shradhagupta@...ux.microsoft.com>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: Bjorn Helgaas <bhelgaas@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>, Marc Zyngier <maz@...nel.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Shivamurthy Shastri <shivamurthy.shastri@...utronix.de>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hyperv@...r.kernel.org,
	Roman Kisel <romank@...ux.microsoft.com>
Subject: Re: [PATCH] PCI/MSI: Initialize the prepare descriptor by default

On Tue, Jul 08, 2025 at 10:48:48AM +0530, Naman Jain wrote:
> Plug the default MSI-X prepare descriptor for non-implemented ops by
> default to workaround the inability of Hyper-V vPCI module to setup
> the MSI-X descriptors properly; especially for dynamically allocated
> MSI-X.
> 
> Signed-off-by: Naman Jain <namjain@...ux.microsoft.com>
> ---
>  drivers/pci/msi/irqdomain.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/drivers/pci/msi/irqdomain.c b/drivers/pci/msi/irqdomain.c
> index 765312c92d9b..655e99b9c8cc 100644
> --- a/drivers/pci/msi/irqdomain.c
> +++ b/drivers/pci/msi/irqdomain.c
> @@ -84,6 +84,8 @@ static void pci_msi_domain_update_dom_ops(struct msi_domain_info *info)
>  	} else {
>  		if (ops->set_desc == NULL)
>  			ops->set_desc = pci_msi_domain_set_desc;
> +		if (ops->prepare_desc == NULL)
> +			ops->prepare_desc = pci_msix_prepare_desc;
>  	}
>  }
>  
> 
> base-commit: 26ffb3d6f02cd0935fb9fa3db897767beee1cb2a
> -- 
> 2.34.1
>

Hey Naman,

can you please try your tests with this patch:
https://lore.kernel.org/all/1749651015-9668-1-git-send-email-shradhagupta@linux.microsoft.com/
I think this should help your use case

Regards,
Shradha.