Re: [PATCH v6 02/22] intel_iommu: Delete RPS capability related supporting code

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

Hi Zhenzhong,

On 9/18/25 10:57 AM, Zhenzhong Duan wrote:
> RID-PASID Support(RPS) is not set in vIOMMU ECAP register, the supporting
> code is there but never take effect.
takes
>
> Meanwhile, according to VTD spec section 3.4.3:
> "Implementations not supporting RID_PASID capability (ECAP_REG.RPS is 0b),
> use a PASID value of 0 to perform address translation for requests without
> PASID."
>
> We should delete the supporting code which fetches RID_PASID field from
> scalable context entry and use 0 as RID_PASID directly, because RID_PASID
> field is ignored if no RPS support according to spec.
>
> This simplify the code and doesn't bring any penalty.
simplifies
>
> Opportunistically, s/rid2pasid/rid_pasid and s/RID2PASID/RID_PASID as
> VTD spec uses RID_PASID terminology.
>
> Suggested-by: Yi Liu <yi.l.liu@intel.com>
> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
> ---
>  hw/i386/intel_iommu_internal.h |  1 -
>  hw/i386/intel_iommu.c          | 49 +++++++++++++---------------------
>  2 files changed, 19 insertions(+), 31 deletions(-)
>
> diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
> index 360e937989..6abe76556a 100644
> --- a/hw/i386/intel_iommu_internal.h
> +++ b/hw/i386/intel_iommu_internal.h
> @@ -547,7 +547,6 @@ typedef struct VTDRootEntry VTDRootEntry;
>  #define VTD_CTX_ENTRY_LEGACY_SIZE     16
>  #define VTD_CTX_ENTRY_SCALABLE_SIZE   32
>  
> -#define VTD_SM_CONTEXT_ENTRY_RID2PASID_MASK 0xfffff
>  #define VTD_SM_CONTEXT_ENTRY_RSVD_VAL0(aw)  (0x1e0ULL | ~VTD_HAW_MASK(aw))
>  #define VTD_SM_CONTEXT_ENTRY_RSVD_VAL1      0xffffffffffe00000ULL
>  
> diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
> index 71b70b795d..b976b251bc 100644
> --- a/hw/i386/intel_iommu.c
> +++ b/hw/i386/intel_iommu.c
> @@ -41,8 +41,7 @@
>  #include "trace.h"
>  
>  /* context entry operations */
> -#define VTD_CE_GET_RID2PASID(ce) \
> -    ((ce)->val[1] & VTD_SM_CONTEXT_ENTRY_RID2PASID_MASK)
> +#define RID_PASID    0
I would call that RID_PASID_0 to make it more explicit in the code
or even it is a PASID to PASID_0 would do the job too.
>  #define VTD_CE_GET_PASID_DIR_TABLE(ce) \
>      ((ce)->val[0] & VTD_PASID_DIR_BASE_ADDR_MASK)
>  
> @@ -951,7 +950,7 @@ static int vtd_ce_get_pasid_entry(IntelIOMMUState *s, VTDContextEntry *ce,
>      int ret = 0;
>  
>      if (pasid == PCI_NO_PASID) {
> -        pasid = VTD_CE_GET_RID2PASID(ce);
> +        pasid = RID_PASID;
>      }
>      pasid_dir_base = VTD_CE_GET_PASID_DIR_TABLE(ce);
>      ret = vtd_get_pe_from_pasid_table(s, pasid_dir_base, pasid, pe);
> @@ -970,7 +969,7 @@ static int vtd_ce_get_pasid_fpd(IntelIOMMUState *s,
>      VTDPASIDEntry pe;
>  
>      if (pasid == PCI_NO_PASID) {
> -        pasid = VTD_CE_GET_RID2PASID(ce);
> +        pasid = RID_PASID;
>      }
>      pasid_dir_base = VTD_CE_GET_PASID_DIR_TABLE(ce);
>  
> @@ -1510,15 +1509,14 @@ static inline int vtd_context_entry_rsvd_bits_check(IntelIOMMUState *s,
>      return 0;
>  }
>  
> -static int vtd_ce_rid2pasid_check(IntelIOMMUState *s,
> +static int vtd_ce_rid_pasid_check(IntelIOMMUState *s,
>                                    VTDContextEntry *ce)
>  {
>      VTDPASIDEntry pe;
>  
>      /*
>       * Make sure in Scalable Mode, a present context entry
> -     * has valid rid2pasid setting, which includes valid
> -     * rid2pasid field and corresponding pasid entry setting
> +     * has valid pasid entry setting at RID_PASID(0).
s/at RID_PASID(0) /for PASID_0?
>       */
>      return vtd_ce_get_pasid_entry(s, ce, &pe, PCI_NO_PASID);
>  }
> @@ -1581,12 +1579,11 @@ static int vtd_dev_to_context_entry(IntelIOMMUState *s, uint8_t bus_num,
>          }
>      } else {
>          /*
> -         * Check if the programming of context-entry.rid2pasid
> -         * and corresponding pasid setting is valid, and thus
> -         * avoids to check pasid entry fetching result in future
> -         * helper function calling.
> +         * Check if the programming of pasid setting at RID_PASID(0)
of pasid 0?
> +         * is valid, and thus avoids to check pasid entry fetching
> +         * result in future helper function calling.
>           */
> -        ret_fr = vtd_ce_rid2pasid_check(s, ce);
> +        ret_fr = vtd_ce_rid_pasid_check(s, ce);
>          if (ret_fr) {
>              return ret_fr;
>          }
> @@ -2097,7 +2094,7 @@ static bool vtd_do_iommu_translate(VTDAddressSpace *vtd_as, PCIBus *bus,
>      bool reads = true;
>      bool writes = true;
>      uint8_t access_flags, pgtt;
> -    bool rid2pasid = (pasid == PCI_NO_PASID) && s->root_scalable;
> +    bool rid_pasid = (pasid == PCI_NO_PASID) && s->root_scalable;
I am not keen of the rid_pasid name. It does not tell what is the
semantic of the variable. rid_pasid is an actual field in the CE.
does that check whether we face a request without pasid in scalable
mode. If so I would call that request_wo_pasid_sm or somethink alike
>      VTDIOTLBEntry *iotlb_entry;
>      uint64_t xlat, size;
>  
> @@ -2111,8 +2108,8 @@ static bool vtd_do_iommu_translate(VTDAddressSpace *vtd_as, PCIBus *bus,
>  
>      cc_entry = &vtd_as->context_cache_entry;
>  
> -    /* Try to fetch pte from IOTLB, we don't need RID2PASID logic */
> -    if (!rid2pasid) {
> +    /* Try to fetch pte from IOTLB, we don't need RID_PASID(0) logic */
It is unclear what the "RID_PASID(0) logic" is. All the more so we now
just have to set the pasid to PASID_0.
> +    if (!rid_pasid) {
>          iotlb_entry = vtd_lookup_iotlb(s, source_id, pasid, addr);
>          if (iotlb_entry) {
>              trace_vtd_iotlb_page_hit(source_id, addr, iotlb_entry->pte,
> @@ -2160,8 +2157,8 @@ static bool vtd_do_iommu_translate(VTDAddressSpace *vtd_as, PCIBus *bus,
>          cc_entry->context_cache_gen = s->context_cache_gen;
>      }
>  
> -    if (rid2pasid) {
> -        pasid = VTD_CE_GET_RID2PASID(&ce);
> +    if (rid_pasid) {
> +        pasid = RID_PASID;
>      }
>  
>      /*
> @@ -2189,8 +2186,8 @@ static bool vtd_do_iommu_translate(VTDAddressSpace *vtd_as, PCIBus *bus,
>          return true;
>      }
>  
> -    /* Try to fetch pte from IOTLB for RID2PASID slow path */
> -    if (rid2pasid) {
> +    /* Try to fetch pte from IOTLB for RID_PASID(0) slow path */
PASID_0?
> +    if (rid_pasid) {
>          iotlb_entry = vtd_lookup_iotlb(s, source_id, pasid, addr);
>          if (iotlb_entry) {
>              trace_vtd_iotlb_page_hit(source_id, addr, iotlb_entry->pte,
> @@ -2464,20 +2461,14 @@ static void vtd_iotlb_page_invalidate_notify(IntelIOMMUState *s,
>          ret = vtd_dev_to_context_entry(s, pci_bus_num(vtd_as->bus),
>                                         vtd_as->devfn, &ce);
>          if (!ret && domain_id == vtd_get_domain_id(s, &ce, vtd_as->pasid)) {
> -            uint32_t rid2pasid = PCI_NO_PASID;
> -
> -            if (s->root_scalable) {
> -                rid2pasid = VTD_CE_GET_RID2PASID(&ce);
> -            }
> -
>              /*
>               * In legacy mode, vtd_as->pasid == pasid is always true.
>               * In scalable mode, for vtd address space backing a PCI
>               * device without pasid, needs to compare pasid with
> -             * rid2pasid of this device.
> +             * RID_PASID(0) of this device.
>               */
>              if (!(vtd_as->pasid == pasid ||
> -                  (vtd_as->pasid == PCI_NO_PASID && pasid == rid2pasid))) {
> +                  (vtd_as->pasid == PCI_NO_PASID && pasid == RID_PASID))) {
would strongly suggest using PASID_0 instead
>                  continue;
>              }
>  
> @@ -2976,9 +2967,7 @@ static void vtd_piotlb_pasid_invalidate(IntelIOMMUState *s,
>          if (!vtd_dev_to_context_entry(s, pci_bus_num(vtd_as->bus),
>                                        vtd_as->devfn, &ce) &&
>              domain_id == vtd_get_domain_id(s, &ce, vtd_as->pasid)) {
> -            uint32_t rid2pasid = VTD_CE_GET_RID2PASID(&ce);
> -
> -            if ((vtd_as->pasid != PCI_NO_PASID || pasid != rid2pasid) &&
> +            if ((vtd_as->pasid != PCI_NO_PASID || pasid != RID_PASID) &&
>                  vtd_as->pasid != pasid) {
>                  continue;
>              }
Thanks

Eric