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 RE: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable nested SMMUv3
->>  >with an error message indicating DMA mapping failed for the
+Hi Daniel,
->> passthrough >devices.
->>
+> -----Original Message-----
->> A correction - the message indicates UEFI failed to find a mapping for
+> From: Daniel P. Berrangé <berrange@redhat.com>
->> the boot partition ("map: no mapping found"), not that DMA mapping
+> Sent: Thursday, January 30, 2025 4:00 PM
->> failed. But earlier EDK debug logs still show PCI host bridge resource
+> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
->> conflicts for the passthrough devices that seem related to the VM boot
+> Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
->> failure.
+> eric.auger@redhat.com; peter.maydell@linaro.org; jgg@nvidia.com;
 > nicolinc@nvidia.com; ddutile@redhat.com; Linuxarm
 > <linuxarm@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>;
 > jiangkunkun <jiangkunkun@huawei.com>; Jonathan Cameron
 > <jonathan.cameron@huawei.com>; zhangfei.gao@linaro.org
 > Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable
 > nested SMMUv3
 >
-> I have tried a 2023 version EFI which works. And for more recent tests I am
+> On Fri, Nov 08, 2024 at 12:52:37PM +0000, Shameer Kolothum via wrote:
-> using a one built directly from,
+> > How to use it(Eg:):
-> https://github.com/tianocore/edk2.git master
+> >
 > > On a HiSilicon platform that has multiple physical SMMUv3s, the ACC ZIP
 > VF
 > > devices and HNS VF devices are behind different SMMUv3s. So for a
 > Guest,
 > > specify two smmuv3-nested devices each behind a pxb-pcie as below,
 > >
 > > ./qemu-system-aarch64 -machine virt,gic-version=3,default-bus-bypass-
 > iommu=on \
 > > -enable-kvm -cpu host -m 4G -smp cpus=8,maxcpus=8 \
 > > -object iommufd,id=iommufd0 \
 > > -bios QEMU_EFI.fd \
 > > -kernel Image \
 > > -device virtio-blk-device,drive=fs \
 > > -drive if=none,file=rootfs.qcow2,id=fs \
 > > -device pxb-pcie,id=pcie.1,bus_nr=8,bus=pcie.0 \
 > > -device pcie-root-port,id=pcie.port1,bus=pcie.1,chassis=1 \
 > > -device arm-smmuv3-nested,id=smmuv1,pci-bus=pcie.1 \
 > > -device vfio-pci,host=0000:7d:02.1,bus=pcie.port1,iommufd=iommufd0 \
 > > -device pxb-pcie,id=pcie.2,bus_nr=16,bus=pcie.0 \
 > > -device pcie-root-port,id=pcie.port2,bus=pcie.2,chassis=2 \
 > > -device arm-smmuv3-nested,id=smmuv2,pci-bus=pcie.2 \
 > > -device vfio-pci,host=0000:75:00.1,bus=pcie.port2,iommufd=iommufd0 \
 > > -append "rdinit=init console=ttyAMA0 root=/dev/vda2 rw
 > earlycon=pl011,0x9000000" \
 > > -device virtio-9p-pci,fsdev=p9fs2,mount_tag=p9,bus=pcie.0 \
 > > -fsdev local,id=p9fs2,path=p9root,security_model=mapped \
 > > -net none \
 > > -nographic
 >
-> Commit: 0f3867fa6ef0("UefiPayloadPkg/UefiPayloadEntry: Fix PT protection
+> Above you say the host has 2 SMMUv3 devices, and you've created 2
-> in 5 level paging"
+> SMMUv3
 > guest devices to match.
 >
-> With both, I don’t remember seeing any boot failure and the above UEFI
+> The various emails in this thread & libvirt thread, indicate that each
-> related "map: no mapping found" error. But the Guest kernel at times
+> guest SMMUv3 is associated with a host SMMUv3, but I don't see any
-> complaints about pci bridge window memory assignment failures.
+> property on the command line for 'arm-ssmv3-nested' that tells it which
-> ...
+> host eSMMUv3 it is to be associated with.
 > pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: can't assign; no space
 > pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: failed to assign
 > pci 0000:10:00.0: bridge window [io  size 0x1000]:can't assign; no space
 > ...
 >
-> But Guest still boots and worked fine so far.
+> How does this association work ?
-Hi Shameer,
+You are right. The association is not very obvious in Qemu. The association
 and checking is done implicitly by kernel at the moment.  I will try to explain
 it here.
-Just letting you know I resolved this by increasing the MMIO region size
+Each "arm-smmuv3-nested" instance, when the first device gets attached
-in hw/arm/virt.c to support passing through GPUs with large BAR regions
+to it, will create a S2 HWPT and a corresponding SMMUv3 domain in kernel
-(VIRT_HIGH_PCIE_MMIO). Thanks for taking a look.
+SMMUv3 driver. This domain will have a pointer representing the physical
 SMMUv3 that the device belongs. And any other device which belongs to
 the same physical SMMUv3 can share this S2 domain.
 If a device that belongs to a different physical SMMUv3 gets attached to
 the above domain, the HWPT attach will eventually fail as the physical
 smmuv3 in the domains will have a mismatch,
 https://elixir.bootlin.com/linux/v6.13/source/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c#L2860
 And as I mentioned in cover letter, Qemu will report,
 "
 Attempt to add the HNS VF to a different SMMUv3 will result in,
 -device vfio-pci,host=0000:7d:02.2,bus=pcie.port3,iommufd=iommufd0: Unable to attach viommu
 -device vfio-pci,host=0000:7d:02.2,bus=pcie.port3,iommufd=iommufd0: vfio 0000:7d:02.2:
    Failed to set iommu_device: [iommufd=29] error attach 0000:7d:02.2 (38) to id=11: Invalid argument
 At present Qemu is not doing any extra validation other than the above
 failure to make sure the user configuration is correct or not. The
 assumption is libvirt will take care of this.
 "
 So in summary, if the libvirt gets it wrong, Qemu will fail with error.
 If a more explicit association is required, some help from kernel is required
 to identify the physical SMMUv3 associated with the device.
 Jason/Nicolin, any thoughts on this?
 Thanks,
-Nathan
+Shameer

>>  >with an error message indicating DMA mapping failed for the
>> passthrough >devices.
>> 
>> A correction - the message indicates UEFI failed to find a mapping for
>> the boot partition ("map: no mapping found"), not that DMA mapping
>> failed. But earlier EDK debug logs still show PCI host bridge resource
>> conflicts for the passthrough devices that seem related to the VM boot
>> failure.
> 
> I have tried a 2023 version EFI which works. And for more recent tests I am
> using a one built directly from,
> https://github.com/tianocore/edk2.git master
> 
> Commit: 0f3867fa6ef0("UefiPayloadPkg/UefiPayloadEntry: Fix PT protection
> in 5 level paging"
> 
> With both, I don’t remember seeing any boot failure and the above UEFI
> related "map: no mapping found" error. But the Guest kernel at times
> complaints about pci bridge window memory assignment failures.
> ...
> pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: can't assign; no space
> pci 0000:10:01.0: bridge window [mem size 0x00200000 64bit pref]: failed to assign
> pci 0000:10:00.0: bridge window [io  size 0x1000]:can't assign; no space
> ...
> 
> But Guest still boots and worked fine so far.

Hi Shameer,

Just letting you know I resolved this by increasing the MMIO region size 
in hw/arm/virt.c to support passing through GPUs with large BAR regions 
(VIRT_HIGH_PCIE_MMIO). Thanks for taking a look.

Thanks,
Nathan

Hi Daniel,

> -----Original Message-----
> From: Daniel P. Berrangé <berrange@redhat.com>
> Sent: Thursday, January 30, 2025 4:00 PM
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@huawei.com>
> Cc: qemu-arm@nongnu.org; qemu-devel@nongnu.org;
> eric.auger@redhat.com; peter.maydell@linaro.org; jgg@nvidia.com;
> nicolinc@nvidia.com; ddutile@redhat.com; Linuxarm
> <linuxarm@huawei.com>; Wangzhou (B) <wangzhou1@hisilicon.com>;
> jiangkunkun <jiangkunkun@huawei.com>; Jonathan Cameron
> <jonathan.cameron@huawei.com>; zhangfei.gao@linaro.org
> Subject: Re: [RFC PATCH 0/5] hw/arm/virt: Add support for user-creatable
> nested SMMUv3
> 
> On Fri, Nov 08, 2024 at 12:52:37PM +0000, Shameer Kolothum via wrote:
> > How to use it(Eg:):
> >
> > On a HiSilicon platform that has multiple physical SMMUv3s, the ACC ZIP
> VF
> > devices and HNS VF devices are behind different SMMUv3s. So for a
> Guest,
> > specify two smmuv3-nested devices each behind a pxb-pcie as below,
> >
> > ./qemu-system-aarch64 -machine virt,gic-version=3,default-bus-bypass-
> iommu=on \
> > -enable-kvm -cpu host -m 4G -smp cpus=8,maxcpus=8 \
> > -object iommufd,id=iommufd0 \
> > -bios QEMU_EFI.fd \
> > -kernel Image \
> > -device virtio-blk-device,drive=fs \
> > -drive if=none,file=rootfs.qcow2,id=fs \
> > -device pxb-pcie,id=pcie.1,bus_nr=8,bus=pcie.0 \
> > -device pcie-root-port,id=pcie.port1,bus=pcie.1,chassis=1 \
> > -device arm-smmuv3-nested,id=smmuv1,pci-bus=pcie.1 \
> > -device vfio-pci,host=0000:7d:02.1,bus=pcie.port1,iommufd=iommufd0 \
> > -device pxb-pcie,id=pcie.2,bus_nr=16,bus=pcie.0 \
> > -device pcie-root-port,id=pcie.port2,bus=pcie.2,chassis=2 \
> > -device arm-smmuv3-nested,id=smmuv2,pci-bus=pcie.2 \
> > -device vfio-pci,host=0000:75:00.1,bus=pcie.port2,iommufd=iommufd0 \
> > -append "rdinit=init console=ttyAMA0 root=/dev/vda2 rw
> earlycon=pl011,0x9000000" \
> > -device virtio-9p-pci,fsdev=p9fs2,mount_tag=p9,bus=pcie.0 \
> > -fsdev local,id=p9fs2,path=p9root,security_model=mapped \
> > -net none \
> > -nographic
> 
> Above you say the host has 2 SMMUv3 devices, and you've created 2
> SMMUv3
> guest devices to match.
> 
> The various emails in this thread & libvirt thread, indicate that each
> guest SMMUv3 is associated with a host SMMUv3, but I don't see any
> property on the command line for 'arm-ssmv3-nested' that tells it which
> host eSMMUv3 it is to be associated with.
> 
> How does this association work ?

You are right. The association is not very obvious in Qemu. The association
and checking is done implicitly by kernel at the moment.  I will try to explain
it here.

Each "arm-smmuv3-nested" instance, when the first device gets attached
to it, will create a S2 HWPT and a corresponding SMMUv3 domain in kernel
SMMUv3 driver. This domain will have a pointer representing the physical
SMMUv3 that the device belongs. And any other device which belongs to
the same physical SMMUv3 can share this S2 domain.

If a device that belongs to a different physical SMMUv3 gets attached to
the above domain, the HWPT attach will eventually fail as the physical
smmuv3 in the domains will have a mismatch,
https://elixir.bootlin.com/linux/v6.13/source/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c#L2860

And as I mentioned in cover letter, Qemu will report,

"
Attempt to add the HNS VF to a different SMMUv3 will result in,

-device vfio-pci,host=0000:7d:02.2,bus=pcie.port3,iommufd=iommufd0: Unable to attach viommu
-device vfio-pci,host=0000:7d:02.2,bus=pcie.port3,iommufd=iommufd0: vfio 0000:7d:02.2:
   Failed to set iommu_device: [iommufd=29] error attach 0000:7d:02.2 (38) to id=11: Invalid argument

At present Qemu is not doing any extra validation other than the above 
failure to make sure the user configuration is correct or not. The
assumption is libvirt will take care of this.
"
So in summary, if the libvirt gets it wrong, Qemu will fail with error.

If a more explicit association is required, some help from kernel is required
to identify the physical SMMUv3 associated with the device.

Jason/Nicolin, any thoughts on this?

Thanks,
Shameer