> -----Original Message-----
> From: Jason Gunthorpe <[email protected]>
> Sent: 04 November 2025 14:21
> To: Eric Auger <[email protected]>
> Cc: Shameer Kolothum <[email protected]>; qemu-
> [email protected]; [email protected]; [email protected];
> Nicolin Chen <[email protected]>; [email protected];
> [email protected]; Nathan Chen <[email protected]>; Matt Ochs
> <[email protected]>; [email protected]; [email protected];
> [email protected]; [email protected];
> [email protected]; [email protected]; [email protected];
> Krishnakant Jaju <[email protected]>
> Subject: Re: [PATCH v5 15/32] hw/pci/pci: Introduce optional
> get_msi_address_space() callback
>
> On Tue, Nov 04, 2025 at 03:11:55PM +0100, Eric Auger wrote:
> > > However, QEMU/KVM also calls this callback when resolving
> > > MSI doorbells:
> > >
> > > kvm_irqchip_add_msi_route()
> > > kvm_arch_fixup_msi_route()
> > > pci_device_iommu_address_space()
> > > get_address_space()
> > >
> > > VFIO device in the guest with a SMMUv3 is programmed with a gIOVA for
> > > MSI doorbell. This gIOVA can't be used to setup the MSI doorbell
> > > directly. This needs to be translated to vITS gPA. In order to do the
> > > doorbell transalation it needs IOMMU address space.
>
> Why does qemu do anything with the msi address? It is opaque and qemu
> cannot determine anything meaningful from it. I expect it to ignore it?
I am afraid not. Guest MSI table write gets trapped and it then configures the
doorbell( this is where this patch comes handy) and sets up the KVM
routing etc.
Thanks,
Shameer
