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

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Message-ID: <20250708160817.GA2148355@bhelgaas>
Date: Tue, 8 Jul 2025 11:08:17 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Naman Jain <namjain@...ux.microsoft.com>
Cc: Shradha Gupta <shradhagupta@...ux.microsoft.com>,
	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 03:45:05PM +0530, Naman Jain wrote:
> On 7/8/2025 3:32 PM, Shradha Gupta wrote:
> > 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
> 
> Hey,
> Thanks for sharing this, this works for me.
> 
> Closing this thread.

I guess this means we should ignore this patch?  If it turns out that
we do need this patch, I'd like to add some details in the commit log
about what this problem looks like to users.

Bjorn