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

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Message-ID: <BN9PR11MB527625E8A9BB854F3C0D19AE8C729@BN9PR11MB5276.namprd11.prod.outlook.com>
Date:   Sat, 11 Dec 2021 07:44:08 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Thomas Gleixner <tglx@...utronix.de>,
        Jason Gunthorpe <jgg@...dia.com>
CC:     "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>, Joerg Roedel <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: Thomas Gleixner <tglx@...utronix.de>
> Sent: Saturday, December 11, 2021 3:00 AM
> 
> Jason,
> 
> On Fri, Dec 10 2021 at 08:39, Jason Gunthorpe wrote:
> 
> > On Fri, Dec 10, 2021 at 07:29:01AM +0000, Tian, Kevin wrote:
> >> >   5) It's not possible for the kernel to reliably detect whether it is
> >> >      running on bare metal or not. Yes we talked about heuristics, but
> >> >      that's something I really want to avoid.
> >>
> >> How would the hypercall mechanism avoid such heuristics?
> >
> > It is clever, we don't have an vIOMMU that supplies vIR today, so by
> > definition all guests are excluded and only bare metal works.
> 
> Dammit. Now you spilled the beans. :)
> 

Unfortunately we do have that today. Qemu supports IR for
both AMD and Intel vIOMMU.

Thanks
Kevin