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

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Date:   Thu, 9 Dec 2021 05:41:14 +0000
From:   "Tian, Kevin" <kevin.tian@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>
CC:     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>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        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: Jason Gunthorpe <jgg@...dia.com>
> Sent: Thursday, December 2, 2021 9:55 PM
> 
> Further, there is no reason why IMS should be reserved exclusively for
> VFIO! 

This is correct. Just as what you agreed with Thomas, the only difference
between IMS and MSI is on where the messages are stored. Physically 
it is unreasonable for the HW to check whether an interrupt is used for
a specific software usage (e.g. virtualization) since it doesn't have such
knowledge. At most an entry is associated to PASID, but again the PASID
can be used anywhere.

The wording in current IDXD spec is not clear on this part. We'll talk to 
the spec owner to have it fixed.

Thanks
Kevin