Hi Zhenzhong,
On 9/18/25 10:57 AM, Zhenzhong Duan wrote:
> When guest enables scalable mode and setup first stage page table, we don't
> want to use IOMMU MR but rather continue using the system MR for IOMMUFD
> backed host device.
>
> Then default HWPT in VFIO contains GPA->HPA mappings which could be reused
> as nesting parent HWPT to construct nested HWPT in vIOMMU.
>
> Suggested-by: Yi Liu <[email protected]>
> Signed-off-by: Zhenzhong Duan <[email protected]>
> ---
> hw/i386/intel_iommu.c | 37 +++++++++++++++++++++++++++++++++++--
> 1 file changed, 35 insertions(+), 2 deletions(-)
>
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index ba40649c85..bd80de1670 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -40,6 +40,7 @@
> #include "kvm/kvm_i386.h"
> #include "migration/vmstate.h"
> #include "trace.h"
> +#include "system/iommufd.h"
>
> /* context entry operations */
> #define RID_PASID 0
> @@ -1702,6 +1703,24 @@ static bool vtd_dev_pt_enabled(IntelIOMMUState *s,
> VTDContextEntry *ce,
>
> }
>
> +static VTDHostIOMMUDevice *vtd_find_hiod_iommufd(VTDAddressSpace *as)
> +{
> + IntelIOMMUState *s = as->iommu_state;
> + struct vtd_as_key key = {
> + .bus = as->bus,
> + .devfn = as->devfn,
> + };
> + VTDHostIOMMUDevice *vtd_hiod = g_hash_table_lookup(s->vtd_host_iommu_dev,
> + &key);
> +
> + if (vtd_hiod && vtd_hiod->hiod &&
> + object_dynamic_cast(OBJECT(vtd_hiod->hiod),
> + TYPE_HOST_IOMMU_DEVICE_IOMMUFD)) {
> + return vtd_hiod;
> + }
> + return NULL;
> +}
> +
> static bool vtd_as_pt_enabled(VTDAddressSpace *as)
> {
> IntelIOMMUState *s;
> @@ -1710,6 +1729,7 @@ static bool vtd_as_pt_enabled(VTDAddressSpace *as)
> assert(as);
>
> s = as->iommu_state;
> +
not needed
> if (vtd_dev_to_context_entry(s, pci_bus_num(as->bus), as->devfn,
> &ce)) {
> /*
> @@ -1727,12 +1747,25 @@ static bool vtd_as_pt_enabled(VTDAddressSpace *as)
> /* Return whether the device is using IOMMU translation. */
> static bool vtd_switch_address_space(VTDAddressSpace *as)
> {
> + IntelIOMMUState *s;
> bool use_iommu, pt;
>
> assert(as);
>
> - use_iommu = as->iommu_state->dmar_enabled && !vtd_as_pt_enabled(as);
> - pt = as->iommu_state->dmar_enabled && vtd_as_pt_enabled(as);
> + s = as->iommu_state;
nit: init could be done at declaration
> + use_iommu = s->dmar_enabled && !vtd_as_pt_enabled(as);
> + pt = s->dmar_enabled && vtd_as_pt_enabled(as);
> +
> + /*
> + * When guest enables scalable mode and setup first stage page table,
sets up?
> + * we stick to system MR for IOMMUFD backed host device. Then its
> + * default hwpt contains GPA->HPA mappings which is used directly
> + * if PGTT=PT and used as nesting parent if PGTT=FST. Otherwise
> + * fallback to original processing.
fall back?
> + */
> + if (s->root_scalable && s->fsts && vtd_find_hiod_iommufd(as)) {
> + use_iommu = false;
> + }
>
> trace_vtd_switch_address_space(pci_bus_num(as->bus),
> VTD_PCI_SLOT(as->devfn),
Besides
Reviewed-by: Eric Auger <[email protected]>
Eric
