linux-kernel - RE: [patch 21/32] NTB/msi: Convert to msi_on_each

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Message-ID: <BN9PR11MB5276D6337528F356B44F18498C4E9@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Thu, 22 Sep 2022 22:42:46 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
CC:     Thomas Gleixner <tglx@...utronix.de>,
        "Chatre, Reinette" <reinette.chatre@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        "Logan Gunthorpe" <logang@...tatee.com>,
        LKML <linux-kernel@...r.kernel.org>,
        "Bjorn Helgaas" <helgaas@...nel.org>,
        Marc Zygnier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        "Dey, Megha" <megha.dey@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Mason <jdmason@...zu.us>, Allen Hubbe <allenbh@...il.com>,
        "linux-ntb@...glegroups.com" <linux-ntb@...glegroups.com>,
        "linux-s390@...r.kernel.org" <linux-s390@...r.kernel.org>,
        Heiko Carstens <hca@...ux.ibm.com>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        "x86@...nel.org" <x86@...nel.org>, "Rodel, Jorg" <jroedel@...e.de>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>
Subject: RE: [patch 21/32] NTB/msi: Convert to msi_on_each_desc()

> From: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, September 22, 2022 8:14 PM
> 
> On Thu, Sep 22, 2022 at 05:11:00AM +0000, Tian, Kevin wrote:
> 
> > > Thinking of the interrupt routing as a host resource is the problem -
> > > it is a device resource and just like PASID the ideal design would
> > > have each RID have its own stable numberspace scoped within it. The
> > > entire RID and all its stable numberspace would be copied over.
> > >
> >
> > Unfortunately it is not the case at least on Intel VT-d. The interrupt
> > remapping table is per VT-d instead of per RID.
> 
> Doesn't that just turn it into a SW problem how it manages it?
> 

When IRTEs are shared cross RID's I'm not sure how to make the
allocation stable between the src and the dest. They are allocated
dynamically and hierarchically in request_irq().

I'm not sure what SW mechanism can cleanly ensure a stable
allocation scheme between two machines.

Can you elaborate?