linux-kernel - Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

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Date:   Sun, 8 Nov 2020 16:05:50 -0800
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     Dan Williams <dan.j.williams@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Jiang, Dave" <dave.jiang@...el.com>,
        Bjorn Helgaas <helgaas@...nel.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "Dey, Megha" <megha.dey@...el.com>,
        "maz@...nel.org" <maz@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Lu, Baolu" <baolu.lu@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Luck, Tony" <tony.luck@...el.com>,
        "kwankhede@...dia.com" <kwankhede@...dia.com>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "parav@...lanox.com" <parav@...lanox.com>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "netanelg@...lanox.com" <netanelg@...lanox.com>,
        "shahafs@...lanox.com" <shahafs@...lanox.com>,
        "yan.y.zhao@...ux.intel.com" <yan.y.zhao@...ux.intel.com>,
        "pbonzini@...hat.com" <pbonzini@...hat.com>,
        "Ortiz, Samuel" <samuel.ortiz@...el.com>,
        "Hossain, Mona" <mona.hossain@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: [PATCH v4 06/17] PCI: add SIOV and IMS capability detection

Hi Jason

On Sun, Nov 08, 2020 at 07:41:42PM -0400, Jason Gunthorpe wrote:
> On Sun, Nov 08, 2020 at 10:11:24AM -0800, Raj, Ashok wrote:
> 
> > > On (kvm) virtualization the addr/data pair the IRQ domain hands out
> > > doesn't work. It is some fake thing.
> > 
> > Is it really some fake thing? I thought the vCPU and vector are real
> > for a guest, and VMM ensures when interrupts are delivered they are either.
> 
> It is fake in the sense it is programmed into no hardware.
>  
> It is real in the sense it is an ABI contract with the VMM.

Ah.. its clear now. That clears up my question below as well.

> 
> Yes, no matter what the VMM has to know the guest wants an interrupt
> routed in and setup the VMM part of the equation. With SRIOV this is
> all done with the MSI trapping.
> 
> > What if the guest creates some addr in the 0xfee... range how do we
> > take care of interrupt remapping and such without any VMM assist?
> 
> Not sure I understand this?
> 

My question was based on mis-conception that interrupt entries are directly
written by guest OS for mlx*. My concern was about security isolation if guest OS
has full control of device interrupt store. 

I think you clarified it, that interrupts still are marshalled by the VMM
and not in direct control of guest OS. That makes my question moot.

Cheers,
Ashok