linux-kernel - Re: [PATCH 6/9] virtio_pci: harden MSI-X interrupts

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Message-ID: <20210913164934-mutt-send-email-mst@kernel.org>
Date:   Mon, 13 Sep 2021 16:54:08 -0400
From:   "Michael S. Tsirkin" <mst@...hat.com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Jason Wang <jasowang@...hat.com>,
        virtualization <virtualization@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "Hetzelt, Felicitas" <f.hetzelt@...berlin.de>,
        "kaplan, david" <david.kaplan@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        pbonzini <pbonzini@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
        Dan Williams <dan.j.williams@...el.com>,
        "Kuppuswamy, Sathyanarayanan" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Andy Lutomirski <luto@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Richard Henderson <rth@...ddle.net>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        James E J Bottomley <James.Bottomley@...senpartnership.com>,
        Helge Deller <deller@....de>,
        "David S . Miller" <davem@...emloft.net>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Peter H Anvin <hpa@...or.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Tony Luck <tony.luck@...el.com>,
        Kirill Shutemov <kirill.shutemov@...ux.intel.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Kuppuswamy Sathyanarayanan <knsathya@...nel.org>,
        X86 ML <x86@...nel.org>
Subject: Re: [PATCH 6/9] virtio_pci: harden MSI-X interrupts

On Mon, Sep 13, 2021 at 09:38:30PM +0200, Thomas Gleixner wrote:
> On Mon, Sep 13 2021 at 15:07, Jason Wang wrote:
> > On Mon, Sep 13, 2021 at 2:50 PM Michael S. Tsirkin <mst@...hat.com> wrote:
> >> > But doen't "irq is disabled" basically mean "we told the hypervisor
> >> > to disable the irq"?  What extractly prevents hypervisor from
> >> > sending the irq even if guest thinks it disabled it?
> >>
> >> More generally, can't we for example blow away the
> >> indir_desc array that we use to keep the ctx pointers?
> >> Won't that be enough?
> >
> > I'm not sure how it is related to the indirect descriptor but an
> > example is that all the current driver will assume:
> >
> > 1) the interrupt won't be raised before virtio_device_ready()
> > 2) the interrupt won't be raised after reset()
> 
> If that assumption exists, then you better keep the interrupt line
> disabled until virtio_device_ready() has completed

started not completed. device is allowed to send
config interrupts right after DRIVER_OK status is set by
virtio_device_ready.

> and disable it again
> before reset() is invoked. That's a question of general robustness and
> not really a question of trusted hypervisors and encrypted guests.

We can do this for some MSIX interrupts, sure. Not for shared interrupts though.

> >> > > > > > > +void vp_disable_vectors(struct virtio_device *vdev)
> >> > > > > > >  {
> >> > > > > > >       struct virtio_pci_device *vp_dev = to_vp_device(vdev);
> >> > > > > > >       int i;
> >> > > > > > > @@ -34,7 +34,20 @@ void vp_synchronize_vectors(struct virtio_device *vdev)
> >> > > > > > >               synchronize_irq(vp_dev->pci_dev->irq);
> 
> Don't you want the same change for non-MSI interrupts?


We can't disable them - these are shared.

> Thanks,
> 
>         tglx