On 1/11/26 8:53 PM, Shameer Kolothum wrote:
> Accelerated SMMUv3 instances rely on the physical SMMUv3 for nested
> translation (guest Stage-1, host Stage-2). In this mode, the guest Stage-1
> tables are programmed directly into hardware, and QEMU must not attempt to
> walk them for translation, as doing so is not reliably safe. For vfio-pci
> endpoints behind such a vSMMU, the only translation QEMU needs to perform
> is for the MSI doorbell used during KVM MSI setup.
>
> Implement the callback so that kvm_arch_fixup_msi_route() can retrieve the
> MSI doorbell GPA directly, instead of attempting a software walk of the
> guest translation tables.
>
> Also introduce an SMMUv3 device property to carry the MSI doorbell GPA.
> This property will be set by the virt machine in a subsequent patch.
>
> Reviewed-by: Nicolin Chen <nicolinc@nvidia.com>
> Signed-off-by: Shameer Kolothum <skolothumtho@nvidia.com>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Eric
> ---
> hw/arm/smmuv3-accel.c | 10 ++++++++++
> hw/arm/smmuv3.c | 2 ++
> include/hw/arm/smmuv3.h | 1 +
> 3 files changed, 13 insertions(+)
>
> diff --git a/hw/arm/smmuv3-accel.c b/hw/arm/smmuv3-accel.c
> index c125974d12..c6ee123cdf 100644
> --- a/hw/arm/smmuv3-accel.c
> +++ b/hw/arm/smmuv3-accel.c
> @@ -393,6 +393,15 @@ static void smmuv3_accel_unset_iommu_device(PCIBus *bus, void *opaque,
> }
> }
>
> +static uint64_t smmuv3_accel_get_msi_gpa(PCIBus *bus, void *opaque, int devfn)
> +{
> + SMMUState *bs = opaque;
> + SMMUv3State *s = ARM_SMMUV3(bs);
> +
> + g_assert(s->msi_gpa);
> + return s->msi_gpa;
> +}
> +
> /*
> * Only allow PCIe bridges, pxb-pcie roots, and GPEX roots so vfio-pci
> * endpoints can sit downstream. Accelerated SMMUv3 requires a vfio-pci
> @@ -497,6 +506,7 @@ static const PCIIOMMUOps smmuv3_accel_ops = {
> .get_viommu_flags = smmuv3_accel_get_viommu_flags,
> .set_iommu_device = smmuv3_accel_set_iommu_device,
> .unset_iommu_device = smmuv3_accel_unset_iommu_device,
> + .get_msi_direct_gpa = smmuv3_accel_get_msi_gpa,
> };
>
> /* Based on SMUUv3 GPBA.ABORT configuration, attach a corresponding HWPT */
> diff --git a/hw/arm/smmuv3.c b/hw/arm/smmuv3.c
> index 7a32afd800..6ed9914b1e 100644
> --- a/hw/arm/smmuv3.c
> +++ b/hw/arm/smmuv3.c
> @@ -1998,6 +1998,8 @@ static const Property smmuv3_properties[] = {
> * Defaults to stage 1
> */
> DEFINE_PROP_STRING("stage", SMMUv3State, stage),
> + /* GPA of MSI doorbell, for SMMUv3 accel use. */
> + DEFINE_PROP_UINT64("msi-gpa", SMMUv3State, msi_gpa, 0),
> };
>
> static void smmuv3_instance_init(Object *obj)
> diff --git a/include/hw/arm/smmuv3.h b/include/hw/arm/smmuv3.h
> index e54ece2d38..5616a8a2be 100644
> --- a/include/hw/arm/smmuv3.h
> +++ b/include/hw/arm/smmuv3.h
> @@ -67,6 +67,7 @@ struct SMMUv3State {
> /* SMMU has HW accelerator support for nested S1 + s2 */
> bool accel;
> struct SMMUv3AccelState *s_accel;
> + uint64_t msi_gpa;
> };
>
> typedef enum {