Re: [PATCH v8 13/23] intel_iommu_accel: Bind/unbind guest page table to host

[Eric Auger <eric.auger@redhat.com>]

Hi Zhenzhong,

On 11/17/25 10:37 AM, Zhenzhong Duan wrote:
> This captures the guest PASID table entry modifications and propagates
> the changes to host to attach a hwpt with type determined per guest IOMMU
> PGTT configuration.
>
> When PGTT=PT, attach PASID_0 to a second stage HWPT(GPA->HPA).
> When PGTT=FST, attach PASID_0 to nested HWPT with nesting parent HWPT
> coming from VFIO.
>
> Co-Authored-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>  hw/i386/intel_iommu_accel.h   |   6 ++
>  include/hw/i386/intel_iommu.h |   1 +
>  hw/i386/intel_iommu.c         |  22 ++++++-
>  hw/i386/intel_iommu_accel.c   | 114 ++++++++++++++++++++++++++++++++++
>  hw/i386/trace-events          |   3 +
>  5 files changed, 143 insertions(+), 3 deletions(-)
>
> diff --git a/hw/i386/intel_iommu_accel.h b/hw/i386/intel_iommu_accel.h
> index dbe6ee6982..1a396c50a0 100644
> --- a/hw/i386/intel_iommu_accel.h
> +++ b/hw/i386/intel_iommu_accel.h
> @@ -16,6 +16,7 @@
>  bool vtd_check_hiod_accel(IntelIOMMUState *s, VTDHostIOMMUDevice *vtd_hiod,
>                            Error **errp);
>  VTDHostIOMMUDevice *vtd_find_hiod_iommufd(VTDAddressSpace *as);
> +bool vtd_bind_guest_pasid(VTDAddressSpace *vtd_as, Error **errp);
>  #else
>  static inline bool vtd_check_hiod_accel(IntelIOMMUState *s,
>                                          VTDHostIOMMUDevice *vtd_hiod,
> @@ -30,5 +31,10 @@ static inline VTDHostIOMMUDevice *vtd_find_hiod_iommufd(VTDAddressSpace *as)
>  {
>      return NULL;
>  }
> +
> +static inline bool vtd_bind_guest_pasid(VTDAddressSpace *vtd_as, Error **errp)
> +{
> +    return true;
> +}
>  #endif
>  #endif
> diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
> index 401322665a..8ce8fe1b75 100644
> --- a/include/hw/i386/intel_iommu.h
> +++ b/include/hw/i386/intel_iommu.h
> @@ -104,6 +104,7 @@ struct VTDAddressSpace {
>      PCIBus *bus;
>      uint8_t devfn;
>      uint32_t pasid;
> +    uint32_t fs_hwpt;
nit use fs_hwpt_id
>      AddressSpace as;
>      IOMMUMemoryRegion iommu;
>      MemoryRegion root;          /* The root container of the device */
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 513b2c85d4..36449bf161 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -88,7 +88,11 @@ static void vtd_pasid_cache_reset_locked(IntelIOMMUState *s)
>      g_hash_table_iter_init(&as_it, s->vtd_address_spaces);
>      while (g_hash_table_iter_next(&as_it, NULL, (void **)&vtd_as)) {
>          VTDPASIDCacheEntry *pc_entry = &vtd_as->pasid_cache_entry;
> -        pc_entry->valid = false;
> +        if (pc_entry->valid) {
> +            pc_entry->valid = false;
> +            /* It's fatal to get failure during reset */
could you elaborate on this. Why is it more fatal on reset that on other
circumstances which do not abort?
> +            vtd_bind_guest_pasid(vtd_as, &error_fatal);
> +        }
>      }
>  }
>  
> @@ -3074,6 +3078,8 @@ static void vtd_pasid_cache_sync_locked(gpointer key, gpointer value,
>      VTDPASIDEntry pe;
>      IOMMUNotifier *n;
>      uint16_t did;
> +    const char *err_prefix = "Attaching to HWPT failed: ";
> +    Error *local_err = NULL;
>  
>      if (vtd_dev_get_pe_from_pasid(vtd_as, &pe)) {
>          if (!pc_entry->valid) {
> @@ -3094,7 +3100,9 @@ static void vtd_pasid_cache_sync_locked(gpointer key, gpointer value,
>              vtd_address_space_unmap(vtd_as, n);
>          }
>          vtd_switch_address_space(vtd_as);
> -        return;
> +
> +        err_prefix = "Detaching from HWPT failed: ";
> +        goto do_bind_unbind;
>      }
>  
>      /*
> @@ -3122,12 +3130,20 @@ static void vtd_pasid_cache_sync_locked(gpointer key, gpointer value,
>      if (!pc_entry->valid) {
>          pc_entry->pasid_entry = pe;
>          pc_entry->valid = true;
> -    } else if (!vtd_pasid_entry_compare(&pe, &pc_entry->pasid_entry)) {
> +    } else if (vtd_pasid_entry_compare(&pe, &pc_entry->pasid_entry)) {
> +        err_prefix = "Replacing HWPT attachment failed: ";
> +    } else {
>          return;
>      }
>  
>      vtd_switch_address_space(vtd_as);
>      vtd_address_space_sync(vtd_as);
> +
> +do_bind_unbind:
> +    /* TODO: Fault event injection into guest, report error to QEMU for now */
> +    if (!vtd_bind_guest_pasid(vtd_as, &local_err)) {
> +        error_reportf_err(local_err, "%s", err_prefix);
> +    }
>  }
>  
>  static void vtd_pasid_cache_sync(IntelIOMMUState *s, VTDPASIDCacheInfo *pc_info)
> diff --git a/hw/i386/intel_iommu_accel.c b/hw/i386/intel_iommu_accel.c
> index ebfc503d64..66570ea919 100644
> --- a/hw/i386/intel_iommu_accel.c
> +++ b/hw/i386/intel_iommu_accel.c
> @@ -13,6 +13,7 @@
>  #include "intel_iommu_internal.h"
>  #include "intel_iommu_accel.h"
>  #include "hw/pci/pci_bus.h"
> +#include "trace.h"
>  
>  bool vtd_check_hiod_accel(IntelIOMMUState *s, VTDHostIOMMUDevice *vtd_hiod,
>                            Error **errp)
> @@ -68,3 +69,116 @@ VTDHostIOMMUDevice *vtd_find_hiod_iommufd(VTDAddressSpace *as)
>      }
>      return NULL;
>  }
> +
> +static bool vtd_create_fs_hwpt(HostIOMMUDeviceIOMMUFD *idev,
> +                               VTDPASIDEntry *pe, uint32_t *fs_hwpt,
> +                               Error **errp)
> +{
> +    struct iommu_hwpt_vtd_s1 vtd = {};
> +
> +    vtd.flags = (VTD_SM_PASID_ENTRY_SRE(pe) ? IOMMU_VTD_S1_SRE : 0) |
> +                (VTD_SM_PASID_ENTRY_WPE(pe) ? IOMMU_VTD_S1_WPE : 0) |
> +                (VTD_SM_PASID_ENTRY_EAFE(pe) ? IOMMU_VTD_S1_EAFE : 0);
> +    vtd.addr_width = vtd_pe_get_fs_aw(pe);
> +    vtd.pgtbl_addr = (uint64_t)vtd_pe_get_fspt_base(pe);
> +
> +    return iommufd_backend_alloc_hwpt(idev->iommufd, idev->devid, idev->hwpt_id,
> +                                      0, IOMMU_HWPT_DATA_VTD_S1, sizeof(vtd),
> +                                      &vtd, fs_hwpt, errp);
> +}
> +
> +static void vtd_destroy_old_fs_hwpt(HostIOMMUDeviceIOMMUFD *idev,
> +                                    VTDAddressSpace *vtd_as)
> +{
> +    if (!vtd_as->fs_hwpt) {
> +        return;
> +    }
> +    iommufd_backend_free_id(idev->iommufd, vtd_as->fs_hwpt);
> +    vtd_as->fs_hwpt = 0;
is it a valid assumption a valid ID cannot be null? Is it documented
somewhere?
> +}
> +
> +static bool vtd_device_attach_iommufd(VTDHostIOMMUDevice *vtd_hiod,
> +                                      VTDAddressSpace *vtd_as, Error **errp)
> +{
> +    HostIOMMUDeviceIOMMUFD *idev = HOST_IOMMU_DEVICE_IOMMUFD(vtd_hiod->hiod);
> +    VTDPASIDEntry *pe = &vtd_as->pasid_cache_entry.pasid_entry;
> +    uint32_t hwpt_id;
nit init to idev->hwpt_id
> +    bool ret;
> +
> +    /*
> +     * We can get here only if flts=on, the supported PGTT is FST or PT.
> +     * Catch invalid PGTT when processing invalidation request to avoid
> +     * attaching to wrong hwpt.
> +     */
> +    if (!vtd_pe_pgtt_is_fst(pe) && !vtd_pe_pgtt_is_pt(pe)) {
> +        error_setg(errp, "Invalid PGTT type %d",
> +                   (uint8_t)VTD_SM_PASID_ENTRY_PGTT(pe));
> +        return false;
> +    }
> +
> +    if (vtd_pe_pgtt_is_pt(pe)) {
> +        hwpt_id = idev->hwpt_id;
> +    } else if (!vtd_create_fs_hwpt(idev, pe, &hwpt_id, errp)) {
> +        return false;
> +    }
and 

if (vtd_pe_pgtt_is_fst(pe)) {
    if ((!vtd_create_fs_hwpt(idev, pe, &hwpt_id, errp) {
        return false;
    }

}
this will match free block below
> +
> +    ret = host_iommu_device_iommufd_attach_hwpt(idev, hwpt_id, errp);
> +    trace_vtd_device_attach_hwpt(idev->devid, vtd_as->pasid, hwpt_id, ret);
> +    if (ret) {
> +        /* Destroy old fs_hwpt if it's a replacement */
> +        vtd_destroy_old_fs_hwpt(idev, vtd_as);
> +        if (vtd_pe_pgtt_is_fst(pe)) {
> +            vtd_as->fs_hwpt = hwpt_id;
> +        }
> +    } else if (vtd_pe_pgtt_is_fst(pe)) {
> +        iommufd_backend_free_id(idev->iommufd, hwpt_id);
> +    }
> +
> +    return ret;
> +}
> +
> +static bool vtd_device_detach_iommufd(VTDHostIOMMUDevice *vtd_hiod,
> +                                      VTDAddressSpace *vtd_as, Error **errp)
> +{
> +    HostIOMMUDeviceIOMMUFD *idev = HOST_IOMMU_DEVICE_IOMMUFD(vtd_hiod->hiod);
> +    IntelIOMMUState *s = vtd_as->iommu_state;
> +    uint32_t pasid = vtd_as->pasid;
> +    bool ret;
> +
> +    if (s->dmar_enabled && s->root_scalable) {
> +        ret = host_iommu_device_iommufd_detach_hwpt(idev, errp);
> +        trace_vtd_device_detach_hwpt(idev->devid, pasid, ret);
> +    } else {
> +        /*
> +         * If DMAR remapping is disabled or guest switches to legacy mode,
> +         * we fallback to the default HWPT which contains shadow page table.
> +         * So guest DMA could still work.
> +         */
> +        ret = host_iommu_device_iommufd_attach_hwpt(idev, idev->hwpt_id, errp);
> +        trace_vtd_device_reattach_def_hwpt(idev->devid, pasid, idev->hwpt_id,
> +                                           ret);
> +    }
> +
> +    if (ret) {
> +        vtd_destroy_old_fs_hwpt(idev, vtd_as);
> +    }
> +
> +    return ret;
> +}
> +
> +bool vtd_bind_guest_pasid(VTDAddressSpace *vtd_as, Error **errp)
I find it a little bit confusing to have bind doing the unbind too.
at least I would rename into vtd_propagate_guest_pasid or something alike.
> +{
> +    VTDPASIDCacheEntry *pc_entry = &vtd_as->pasid_cache_entry;
> +    VTDHostIOMMUDevice *vtd_hiod = vtd_find_hiod_iommufd(vtd_as);
> +
> +    /* Ignore emulated device or legacy VFIO backed device */
> +    if (!vtd_as->iommu_state->fsts || !vtd_hiod) {
> +        return true;
> +    }
> +
> +    if (pc_entry->valid) {
> +        return vtd_device_attach_iommufd(vtd_hiod, vtd_as, errp);
> +    }
> +
> +    return vtd_device_detach_iommufd(vtd_hiod, vtd_as, errp);
> +}
> diff --git a/hw/i386/trace-events b/hw/i386/trace-events
> index b704f4f90c..5a3ee1cf64 100644
> --- a/hw/i386/trace-events
> +++ b/hw/i386/trace-events
> @@ -73,6 +73,9 @@ vtd_warn_invalid_qi_tail(uint16_t tail) "tail 0x%"PRIx16
>  vtd_warn_ir_vector(uint16_t sid, int index, int vec, int target) "sid 0x%"PRIx16" index %d vec %d (should be: %d)"
>  vtd_warn_ir_trigger(uint16_t sid, int index, int trig, int target) "sid 0x%"PRIx16" index %d trigger %d (should be: %d)"
>  vtd_reset_exit(void) ""
> +vtd_device_attach_hwpt(uint32_t dev_id, uint32_t pasid, uint32_t hwpt_id, int ret) "dev_id %d pasid %d hwpt_id %d, ret: %d"
> +vtd_device_detach_hwpt(uint32_t dev_id, uint32_t pasid, int ret) "dev_id %d pasid %d ret: %d"
> +vtd_device_reattach_def_hwpt(uint32_t dev_id, uint32_t pasid, uint32_t hwpt_id, int ret) "dev_id %d pasid %d hwpt_id %d, ret: %d"
>  
>  # amd_iommu.c
>  amdvi_evntlog_fail(uint64_t addr, uint32_t head) "error: fail to write at addr 0x%"PRIx64" +  offset 0x%"PRIx32
Thanks

Eric