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

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Message-ID: <8735n1zaz3.ffs@tglx>
Date:   Thu, 09 Dec 2021 23:09:52 +0100
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     "Tian, Kevin" <kevin.tian@...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>, 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 09 2021 at 16:58, Jason Gunthorpe wrote:
> On Thu, Dec 09, 2021 at 09:32:42PM +0100, Thomas Gleixner wrote:
>> That was my thought to avoid having different mechanisms.
>> 
>> The address/data pair is computed in two places:
>> 
>>   1) Activation of an interrupt
>>   2) Affinity setting on an interrupt
>> 
>> Both configure the IRTE when interrupt remapping is in place.
>> 
>> In both cases a vector is allocated in the vector domain and based on
>> the resulting target APIC / vector number pair the IRTE is
>> (re)configured.
>> 
>> So putting the hypercall into the vIRTE update is the obvious
>> place. Both activation and affinity setting can fail and propagate an
>> error code down to the originating caller.
>> 
>> Hmm?
>
> Okay, I think I get it. Would be nice to have someone from intel
> familiar with the vIOMMU protocols and qemu code remark what the
> hypervisor side can look like.
>
> There is a bit more work here, we'd have to change VFIO to somehow
> entirely disconnect the kernel IRQ logic from the MSI table and
> directly pass control of it to the guest after the hypervisor IOMMU IR
> secures it. ie directly mmap the msi-x table into the guest

That makes everything consistent and a clear cut on all levels, right?

Thanks,

        tglx