Hi Eric,
>-----Original Message-----
>From: Eric Auger <[email protected]>
>Subject: Re: [PATCH v6 09/22] intel_iommu: Stick to system MR for
>IOMMUFD backed host device when x-fls=on
>
>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
Will do.
>> 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
Not exactly, it must be after "assert(as);"
>> + 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?
Sure
>> + * 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?
Sure
Thanks
Zhenzhong
>> + */
>> + 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
>
