linux-kernel - Re: [patch 22/33] genirq/msi: Provide MSI_FLAG_MSIX_ALLOC

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Date:   Wed, 16 Nov 2022 15:36:50 -0400
From:   Jason Gunthorpe <jgg@...dia.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>,
        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>,
        Ashok Raj <ashok.raj@...el.com>, Jon Mason <jdmason@...zu.us>,
        Allen Hubbe <allenbh@...il.com>,
        "Ahmed S. Darwish" <darwi@...utronix.de>,
        Reinette Chatre <reinette.chatre@...el.com>
Subject: Re: [patch 22/33] genirq/msi: Provide MSI_FLAG_MSIX_ALLOC_DYN

On Fri, Nov 11, 2022 at 02:58:46PM +0100, Thomas Gleixner wrote:
> Provide a new MSI feature flag in preparation for dynamic MSIX allocation
> after the initial MSI-X enable has been done.
> 
> This needs to be an explicit MSI interrupt domain feature because quite
> some implementations (both interrupt domains and legacy allocation mode)
> have clear expectations that the allocation code is only invoked when MSI-X
> is about to be enabled. They either talk to hypervisors or do some other
> work and are not prepared to be invoked on an already MSI-X enabled device.
> 
> This is also explicit MSI-X only because rewriting the size of the MSI
> entries is only possible when disabling MSI which in turn might cause lost
> interrupts on the device.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> ---
>  include/linux/msi.h |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason