Re: [Xen-devel] [PATCH 2/2] vpci/msi: fix update of bound MSI interrupts

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, May 14, 2018 at 06:29:37AM -0600, Jan Beulich wrote:
> >>> On 08.05.18 at 11:25, <roger.pau@xxxxxxxxxx> wrote:
> > --- a/xen/arch/x86/hvm/vmsi.c
> > +++ b/xen/arch/x86/hvm/vmsi.c
> > @@ -699,6 +699,29 @@ static int vpci_msi_update(const struct pci_dev *pdev, 
> > uint32_t data,
> >      return 0;
> >  }
> >  
> > +int vpci_msi_arch_update(struct vpci_msi *msi, const struct pci_dev *pdev)
> > +{
> > +    int rc;
> > +
> > +    ASSERT(msi->arch.pirq != INVALID_PIRQ);
> > +
> > +    pcidevs_lock();
> > +    rc = vpci_msi_update(pdev, msi->data, msi->address, msi->vectors,
> > +                         msi->arch.pirq, msi->mask);
> > +    if ( rc )
> > +    {
> > +        spin_lock(&pdev->domain->event_lock);
> > +        unmap_domain_pirq(pdev->domain, msi->arch.pirq);
> 
> This looks quite undesirable - a failed update should leave the interrupt in 
> its
> prior state rather than unbinding it. Is that overly difficult to achieve?

Oh, TBH I would expect that writing an invalid data or address fields
will disable MSI instead of keep using the old values. I'm not sure I
see the reason to keep using the old values, certainly that could make
something else go very wonky inside of the guest itself.

Thanks, Roger.

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