linux-kernel - Re: [patch 02/39] iommu/vt-d: Remove bogus check for multi MSI-X

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Message-ID: <Y3UgVEGRIuim+7es@a4bf019067fa.jf.intel.com>
Date:   Wed, 16 Nov 2022 09:39:32 -0800
From:   Ashok Raj <ashok.raj@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>
CC:     LKML <linux-kernel@...r.kernel.org>, <x86@...nel.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        <linux-pci@...r.kernel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
        "Lorenzo Pieralisi" <lorenzo.pieralisi@....com>,
        Marc Zyngier <maz@...nel.org>,
        "Greg Kroah-Hartman" <gregkh@...uxfoundation.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Kevin Tian <kevin.tian@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Jon Mason <jdmason@...zu.us>, Allen Hubbe <allenbh@...il.com>,
        Michael Ellerman <mpe@...erman.id.au>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        <linuxppc-dev@...ts.ozlabs.org>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Reinette Chatre <reinette.chatre@...el.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [patch 02/39] iommu/vt-d: Remove bogus check for multi MSI-X

On Wed, Nov 16, 2022 at 06:02:30PM +0100, Thomas Gleixner wrote:
> On Wed, Nov 16 2022 at 07:52, Ashok Raj wrote:
> > On Fri, Nov 11, 2022 at 02:54:17PM +0100, Thomas Gleixner wrote:
> >> PCI/Multi-MSI is MSI specific and not supported for MSI-X.
> >> 
> >> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> >> ---
> >>  drivers/iommu/intel/irq_remapping.c |    3 +--
> >>  1 file changed, 1 insertion(+), 2 deletions(-)
> >> 
> >> --- a/drivers/iommu/intel/irq_remapping.c
> >> +++ b/drivers/iommu/intel/irq_remapping.c
> >> @@ -1334,8 +1334,7 @@ static int intel_irq_remapping_alloc(str
> >>  
> >>  	if (!info || !iommu)
> >>  		return -EINVAL;
> >> -	if (nr_irqs > 1 && info->type != X86_IRQ_ALLOC_TYPE_PCI_MSI &&
> >> -	    info->type != X86_IRQ_ALLOC_TYPE_PCI_MSIX)
> >> +	if (nr_irqs > 1 && info->type != X86_IRQ_ALLOC_TYPE_PCI_MSI)
> >>  		return -EINVAL;
> >>  
> >>  	/*
> >> 
> >
> > This check is only making sure that when multi-msi is requested that the
> > type has to be either MSI/MSIX.
> 
> MSI-X does not support multi vector allocations on a single entry.
> 
> > Wouldn't this change return -EINVAL when type = MSIX?
> 
> Rightfully so. MSIX vectors are allocated one by one. Has been that way
> forever.
> 

I thought why block multi-vector allocation on MSIX, but if there is no
use case makes perfect sense.

Thanks for the clarification.

Reviewed-by: Ashok Raj <ashok.raj@...el.com>