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

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Date:   Thu, 9 Dec 2021 13:47:17 +0800
From:   Jason Wang <jasowang@...hat.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     Jason Gunthorpe <jgg@...dia.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        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()

On Thu, Dec 9, 2021 at 1:41 PM Tian, Kevin <kevin.tian@...el.com> wrote:
>
> > 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.

Note that vDPA had the plan to use IMS for the parent that can have a
huge amount of instances.

Thanks

>
> 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
>