Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has PCIe Root Complex association

[Jonathan Cameron via <qemu-devel@nongnu.org>]

On Thu, 19 Jun 2025 09:05:07 +0100
Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com> wrote:

> > -----Original Message-----
> > From: Eric Auger <eric.auger@redhat.com>
> > Sent: Thursday, June 19, 2025 8:41 AM
> > To: Shameerali Kolothum Thodi
> > <shameerali.kolothum.thodi@huawei.com>; Jonathan Cameron
> > <jonathan.cameron@huawei.com>
> > Cc: Linuxarm <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has PCIe
> > Root Complex association
> > 
> > Hi Shameer,
> > 
> > On 6/19/25 9:24 AM, Shameerali Kolothum Thodi wrote:  
> > > Hi Eric,
> > >  
> > >> -----Original Message-----
> > >> From: Eric Auger <eric.auger@redhat.com>
> > >> Sent: Wednesday, June 18, 2025 6:00 PM
> > >> To: Shameerali Kolothum Thodi
> > >> <shameerali.kolothum.thodi@huawei.com>; Jonathan Cameron
> > >> <jonathan.cameron@huawei.com>
> > >> Cc: Linuxarm <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > >> devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > >> nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > >> imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > >> smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > >> jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > >> Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has  
> > PCIe  
> > >> Root Complex association
> > >>
> > >> Hi Shameer, Jonathan,
> > >>
> > >> On 6/18/25 10:35 AM, Shameerali Kolothum Thodi wrote:  
> > >>>> -----Original Message-----
> > >>>> From: Jonathan Cameron <jonathan.cameron@huawei.com>
> > >>>> Sent: Tuesday, June 17, 2025 5:53 PM
> > >>>> To: Eric Auger <eric.auger@redhat.com>
> > >>>> Cc: Shameerali Kolothum Thodi
> > >>>> <shameerali.kolothum.thodi@huawei.com>; Linuxarm
> > >>>> <linuxarm@huawei.com>; qemu-arm@nongnu.org; qemu-
> > >>>> devel@nongnu.org; peter.maydell@linaro.org; jgg@nvidia.com;
> > >>>> nicolinc@nvidia.com; ddutile@redhat.com; berrange@redhat.com;
> > >>>> imammedo@redhat.com; nathanc@nvidia.com; mochs@nvidia.com;
> > >>>> smostafa@google.com; Wangzhou (B) <wangzhou1@hisilicon.com>;
> > >>>> jiangkunkun <jiangkunkun@huawei.com>; zhangfei.gao@linaro.org
> > >>>> Subject: Re: [PATCH v4 1/7] hw/arm/smmu-common: Check SMMU has  
> > >> PCIe  
> > >>>> Root Complex association
> > >>>>
> > >>>> On Tue, 17 Jun 2025 09:49:54 +0200
> > >>>> Eric Auger <eric.auger@redhat.com> wrote:
> > >>>>  
> > >>>>> On 6/16/25 12:20 PM, Jonathan Cameron wrote:  
> > >>>>>> On Fri, 13 Jun 2025 15:44:43 +0100
> > >>>>>> Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>  
> > wrote:  
> > >>>>>>  
> > >>>>>>> Although this change does not affect functionality at present, it is  
> > >>>>>> Patch title says PCIe.  This check is vs PCI host bridge.
> > >>>>>>
> > >>>>>> No idea which one you wanted, but if it is PCIe needs to be
> > >>>>>> TYPC_PCIE_HOST_BRIDGE from pcie_host.h not the pci_host.h one
> > >>>>>> I think.  
> > >>>>> I think we need TYPE_PCI_HOST_BRIDGE as we want to check against  
> > >> pxb  
> > >>>>> pci-bridge/pci_expander_bridge.c:    .parent        =  
> > >>>> TYPE_PCI_HOST_BRIDGE,  
> > >> sorry but I still fail to understand why we can't just check against
> > >>
> > >> TYPE_PCI_HOST_BRIDGE for making sure the SMMU is attached to PXB or
> > >> GPEX. What does it fail to check? Why shall we care about PCI vs PCIe?  
> > > I think the concern is  getting any other TYPE_PCI_HOST_BRIDGE types  
> > attached  
> > > to SMMUv3 other than pxb-pcie or GPEX. For example you could do,
> > >
> > > -device pxb-cxl,bus_nr=12,bus=pcie.0,id=cxl.1 \
> > > -device arm-smmuv3,primary-bus=cxl.1,id=smmuv3.1 \
> > >
> > > as pxb-cxl is of type TYPE_PCI_HOST_BRIDGE. I don't know if there are any  
> > other  
> > > ones similar to this out there.
> > >
> > > So the aim is to make the checking more specific to PXB.  
> > 
> > thank you for the clarification. Is it invalid to have the SMMU
> > protecting RIDs comming from the pxb-cxl hierarchy?  
> 
> That’s a good question. I don't know that for sure.

It should be fine to support CXL for this but we can work that out later.

For now limited use cases as there is no CXL VFIO support and the only thing
emulated devices do that the SMMU might influence is MSIX.

The one that concerned me is pxb-pci if we only care about pcie.
I'm not sure if we need to make that distinction or not.  

Jonathan

> Anyway currently the full support for CXL on virt is in progress here,
> https://lore.kernel.org/qemu-devel/20250612134338.1871023-1-Jonathan.Cameron@huawei.com/
> 
> Jonathan?
> 
> Thanks,
> Shameer
> 
> >   
>