[RFC,v3.1,12/22] intel_iommu: add PASID cache management infrastructure
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Message ID 1582358843-51931-13-git-send-email-yi.l.liu@intel.com
State New
Headers show
Series
  • intel_iommu: expose Shared Virtual Addressing to VMs
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Commit Message

Liu, Yi L Feb. 22, 2020, 8:07 a.m. UTC
This patch adds a PASID cache management infrastructure based on
new added structure VTDPASIDAddressSpace, which is used to track
the PASID usage and future PASID tagged DMA address translation
support in vIOMMU.

    struct VTDPASIDAddressSpace {
        VTDBus *vtd_bus;
        uint8_t devfn;
        AddressSpace as;
        uint32_t pasid;
        IntelIOMMUState *iommu_state;
        VTDContextCacheEntry context_cache_entry;
        QLIST_ENTRY(VTDPASIDAddressSpace) next;
        VTDPASIDCacheEntry pasid_cache_entry;
    };

Ideally, a VTDPASIDAddressSpace instance is created when a PASID
is bound with a DMA AddressSpace. Intel VT-d spec requires guest
software to issue pasid cache invalidation when bind or unbind a
pasid with an address space under caching-mode. However, as
VTDPASIDAddressSpace instances also act as pasid cache in this
implementation, its creation also happens during vIOMMU PASID
tagged DMA translation. The creation in this path will not be
added in this patch since no PASID-capable emulated devices for
now.

The implementation in this patch manages VTDPASIDAddressSpace
instances per PASID+BDF (lookup and insert will use PASID and
BDF) since Intel VT-d spec allows per-BDF PASID Table. When a
guest bind a PASID with an AddressSpace, QEMU will capture the
guest pasid selective pasid cache invalidation, and allocate
remove a VTDPASIDAddressSpace instance per the invalidation
reasons:

    *) a present pasid entry moved to non-present
    *) a present pasid entry to be a present entry
    *) a non-present pasid entry moved to present

vIOMMU emulator could figure out the reason by fetching latest
guest pasid entry.

Cc: Kevin Tian <kevin.tian@intel.com>
Cc: Jacob Pan <jacob.jun.pan@linux.intel.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Yi Sun <yi.y.sun@linux.intel.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Liu Yi L <yi.l.liu@intel.com>
---
 hw/i386/intel_iommu.c          | 386 +++++++++++++++++++++++++++++++++++++++++
 hw/i386/intel_iommu_internal.h |  14 ++
 hw/i386/trace-events           |   1 +
 include/hw/i386/intel_iommu.h  |  33 +++-
 4 files changed, 433 insertions(+), 1 deletion(-)

Patch
diff mbox series

diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c
index 462449c..b032a7c 100644
--- a/hw/i386/intel_iommu.c
+++ b/hw/i386/intel_iommu.c
@@ -40,6 +40,7 @@ 
 #include "kvm_i386.h"
 #include "migration/vmstate.h"
 #include "trace.h"
+#include "qemu/jhash.h"
 
 /* context entry operations */
 #define VTD_CE_GET_RID2PASID(ce) \
@@ -65,6 +66,8 @@ 
 static void vtd_address_space_refresh_all(IntelIOMMUState *s);
 static void vtd_address_space_unmap(VTDAddressSpace *as, IOMMUNotifier *n);
 
+static void vtd_pasid_cache_reset(IntelIOMMUState *s);
+
 static void vtd_panic_require_caching_mode(void)
 {
     error_report("We need to set caching-mode=on for intel-iommu to enable "
@@ -276,6 +279,7 @@  static void vtd_reset_caches(IntelIOMMUState *s)
     vtd_iommu_lock(s);
     vtd_reset_iotlb_locked(s);
     vtd_reset_context_cache_locked(s);
+    vtd_pasid_cache_reset(s);
     vtd_iommu_unlock(s);
 }
 
@@ -686,6 +690,11 @@  static inline bool vtd_pe_type_check(X86IOMMUState *x86_iommu,
     return true;
 }
 
+static inline uint16_t vtd_pe_get_domain_id(VTDPASIDEntry *pe)
+{
+    return VTD_SM_PASID_ENTRY_DID((pe)->val[1]);
+}
+
 static inline bool vtd_pdire_present(VTDPASIDDirEntry *pdire)
 {
     return pdire->val & 1;
@@ -2393,19 +2402,394 @@  static bool vtd_process_iotlb_desc(IntelIOMMUState *s, VTDInvDesc *inv_desc)
     return true;
 }
 
+static inline void vtd_init_pasid_key(uint32_t pasid,
+                                     uint16_t sid,
+                                     struct pasid_key *key)
+{
+    key->pasid = pasid;
+    key->sid = sid;
+}
+
+static guint vtd_pasid_as_key_hash(gconstpointer v)
+{
+    struct pasid_key *key = (struct pasid_key *)v;
+    uint32_t a, b, c;
+
+    /* Jenkins hash */
+    a = b = c = JHASH_INITVAL + sizeof(*key);
+    a += key->sid;
+    b += extract32(key->pasid, 0, 16);
+    c += extract32(key->pasid, 16, 16);
+
+    __jhash_mix(a, b, c);
+    __jhash_final(a, b, c);
+
+    return c;
+}
+
+static gboolean vtd_pasid_as_key_equal(gconstpointer v1, gconstpointer v2)
+{
+    const struct pasid_key *k1 = v1;
+    const struct pasid_key *k2 = v2;
+
+    return (k1->pasid == k2->pasid) && (k1->sid == k2->sid);
+}
+
+static inline int vtd_dev_get_pe_from_pasid(IntelIOMMUState *s,
+                                            uint8_t bus_num,
+                                            uint8_t devfn,
+                                            uint32_t pasid,
+                                            VTDPASIDEntry *pe)
+{
+    VTDContextEntry ce;
+    int ret;
+    dma_addr_t pasid_dir_base;
+
+    if (!s->root_scalable) {
+        return -VTD_FR_PASID_TABLE_INV;
+    }
+
+    ret = vtd_dev_to_context_entry(s, bus_num, devfn, &ce);
+    if (ret) {
+        return ret;
+    }
+
+    pasid_dir_base = VTD_CE_GET_PASID_DIR_TABLE(&ce);
+    ret = vtd_get_pe_from_pasid_table(s,
+                                  pasid_dir_base, pasid, pe);
+
+    return ret;
+}
+
+static bool vtd_pasid_entry_compare(VTDPASIDEntry *p1, VTDPASIDEntry *p2)
+{
+    return !memcmp(p1, p2, sizeof(*p1));
+}
+
+/**
+ * This function is used to clear pasid_cache_gen of cached pasid
+ * entry in vtd_pasid_as instances. Caller of this function should
+ * hold iommu_lock.
+ */
+static gboolean vtd_flush_pasid(gpointer key, gpointer value,
+                                gpointer user_data)
+{
+    VTDPASIDCacheInfo *pc_info = user_data;
+    VTDPASIDAddressSpace *vtd_pasid_as = value;
+    IntelIOMMUState *s = vtd_pasid_as->iommu_state;
+    VTDPASIDCacheEntry *pc_entry = &vtd_pasid_as->pasid_cache_entry;
+    VTDBus *vtd_bus = vtd_pasid_as->vtd_bus;
+    VTDPASIDEntry pe;
+    uint16_t did;
+    uint32_t pasid;
+    uint16_t devfn;
+    int ret;
+
+    did = vtd_pe_get_domain_id(&pc_entry->pasid_entry);
+    pasid = vtd_pasid_as->pasid;
+    devfn = vtd_pasid_as->devfn;
+
+    if (!(pc_entry->pasid_cache_gen == s->pasid_cache_gen)) {
+        return false;
+    }
+
+    switch (pc_info->flags & VTD_PASID_CACHE_INFO_MASK) {
+    case VTD_PASID_CACHE_PASIDSI:
+        if (pc_info->pasid != pasid) {
+            return false;
+        }
+        /* Fall through */
+    case VTD_PASID_CACHE_DOMSI:
+        if (pc_info->domain_id != did) {
+            return false;
+        }
+        /* Fall through */
+    case VTD_PASID_CACHE_GLOBAL:
+        break;
+    default:
+        error_report("invalid pc_info->flags");
+        abort();
+    }
+
+    /*
+     * pasid cache invalidation may indicate a present pasid
+     * entry to present pasid entry modification. To cover such
+     * case, vIOMMU emulator needs to fetch latest guest pasid
+     * entry and check cached pasid entry, then update pasid
+     * cache and send pasid bind/unbind to host properly.
+     */
+    ret = vtd_dev_get_pe_from_pasid(s,
+                  pci_bus_num(vtd_bus->bus), devfn, pasid, &pe);
+    if (ret) {
+        /*
+         * No valid pasid entry in guest memory. e.g. pasid entry
+         * was modified to be either all-zero or non-present. Either
+         * case means existing pasid cache should be removed.
+         */
+        goto remove;
+    }
+    /* Compare cached pasid entry and latest pasid entry */
+    if (!vtd_pasid_entry_compare(&pe, &pc_entry->pasid_entry)) {
+        /* pasid entry was updated, thus update the pasid cache */
+        pc_entry->pasid_entry = pe;
+        pc_entry->pasid_cache_gen = s->pasid_cache_gen;
+        /*
+         * TODO:
+         * - send pasid bind to host for passthru devices
+         * - when pasid-base-iotlb(piotlb) infrastructure is ready,
+         *   should invalidate QEMU piotlb togehter with this change.
+         */
+    }
+    return false;
+remove:
+    /*
+     * TODO:
+     * - send pasid unbind to host for passthru devices
+     * - when pasid-base-iotlb(piotlb) infrastructure is ready,
+     *   should invalidate QEMU piotlb togehter with this change.
+     */
+    return true;
+}
+
 static int vtd_pasid_cache_dsi(IntelIOMMUState *s, uint16_t domain_id)
 {
+    VTDPASIDCacheInfo pc_info;
+
+    trace_vtd_pasid_cache_dsi(domain_id);
+
+    pc_info.flags = VTD_PASID_CACHE_DOMSI;
+    pc_info.domain_id = domain_id;
+
+    /*
+     * Loop all existing pasid caches and update them.
+     */
+    vtd_iommu_lock(s);
+    g_hash_table_foreach_remove(s->vtd_pasid_as,
+                                 vtd_flush_pasid, &pc_info);
+    vtd_iommu_unlock(s);
+
+    /*
+     * TODO: Domain selective PASID cache invalidation
+     * flushes all the pasid caches within a domain. To
+     * be safe, after invalidating the pasid caches, emulator
+     * needs to replay the pasid bindings by walking guest
+     * pasid dir and pasid table. e.g. When the guest setup a
+     * new PASID entry then send a PASID DSI.
+     */
     return 0;
 }
 
+/**
+ * This function finds or adds a VTDPASIDAddressSpace for a device
+ * when it is bound to a pasid. Caller of this function should hold
+ * iommu_lock.
+ */
+static VTDPASIDAddressSpace *vtd_add_find_pasid_as(IntelIOMMUState *s,
+                                                   VTDBus *vtd_bus,
+                                                   int devfn,
+                                                   uint32_t pasid)
+{
+    struct pasid_key key;
+    struct pasid_key *new_key;
+    VTDPASIDAddressSpace *vtd_pasid_as;
+    uint16_t sid;
+
+    sid = vtd_make_source_id(pci_bus_num(vtd_bus->bus), devfn);
+    vtd_init_pasid_key(pasid, sid, &key);
+    vtd_pasid_as = g_hash_table_lookup(s->vtd_pasid_as, &key);
+
+    if (!vtd_pasid_as) {
+        new_key = g_malloc0(sizeof(*new_key));
+        vtd_init_pasid_key(pasid, sid, new_key);
+        /*
+         * Initiate the vtd_pasid_as structure.
+         *
+         * This structure here is used to track the guest pasid
+         * binding and also serves as pasid-cache mangement entry.
+         *
+         * TODO: in future, if wants to support the SVA-aware DMA
+         *       emulation, the vtd_pasid_as should have include
+         *       AddressSpace to support DMA emulation.
+         */
+        vtd_pasid_as = g_malloc0(sizeof(VTDPASIDAddressSpace));
+        vtd_pasid_as->iommu_state = s;
+        vtd_pasid_as->vtd_bus = vtd_bus;
+        vtd_pasid_as->devfn = devfn;
+        vtd_pasid_as->context_cache_entry.context_cache_gen = 0;
+        vtd_pasid_as->pasid = pasid;
+        vtd_pasid_as->pasid_cache_entry.pasid_cache_gen = 0;
+        g_hash_table_insert(s->vtd_pasid_as, new_key, vtd_pasid_as);
+    }
+    return vtd_pasid_as;
+}
+
+ /**
+  * This function cached the pasid entry in &vtd_pasid_as.
+  * Caller of this function should hold iommu_lock.
+  */
+static inline void vtd_fill_in_pe_cache(
+              VTDPASIDAddressSpace *vtd_pasid_as, VTDPASIDEntry *pe)
+{
+    IntelIOMMUState *s = vtd_pasid_as->iommu_state;
+    VTDPASIDCacheEntry *pc_entry = &vtd_pasid_as->pasid_cache_entry;
+
+    pc_entry->pasid_entry = *pe;
+    pc_entry->pasid_cache_gen = s->pasid_cache_gen;
+}
+
+/**
+ * Caller of this function should hold iommu_lock
+ */
+static void vtd_new_pasid_bind_for_dev(IntelIOMMUState *s, VTDBus *vtd_bus,
+                                       uint16_t devfn, uint16_t domain_id,
+                                       uint32_t pasid)
+{
+    VTDPASIDAddressSpace *vtd_pasid_as;
+    VTDPASIDEntry pe;
+    VTDPASIDCacheEntry *pc_entry;
+    int bus_n = pci_bus_num(vtd_bus->bus);
+
+    /* i) fetch vtd_pasid_as and check if it is valid */
+    vtd_pasid_as = vtd_add_find_pasid_as(s, vtd_bus,
+                                         devfn, pasid);
+    pc_entry = &vtd_pasid_as->pasid_cache_entry;
+    if (s->pasid_cache_gen == pc_entry->pasid_cache_gen) {
+        /*
+         * pasid_cache_gen equals to s->pasid_cache_gen means
+         * vtd_pasid_as is valid after the above s->vtd_pasid_as
+         * updates. Thus no need for the below steps.
+         */
+        return;
+    }
+
+    /*
+     * ii) vtd_pasid_as is not valid, it's potentailly a new
+     *    pasid bind. Fetch guest pasid entry.
+     */
+    if (vtd_dev_get_pe_from_pasid(s, bus_n, devfn, pasid, &pe)) {
+        return;
+    }
+
+    /*
+     * iii) pasid entry exists, update pasid cache
+     *
+     * Here need to check domain ID since guest pasid entry
+     * exists. What needs to do are:
+     *   - update the pc_entry in the vtd_pasid_as
+     *   - set proper pc_entry.pasid_cache_gen
+     *   - pass down the latest guest pasid entry config to host
+     *     (will be added in later patch)
+     */
+    if (domain_id == vtd_pe_get_domain_id(&pe)) {
+        vtd_fill_in_pe_cache(vtd_pasid_as, &pe);
+    }
+}
+
 static int vtd_pasid_cache_psi(IntelIOMMUState *s,
                                uint16_t domain_id, uint32_t pasid)
 {
+    VTDPASIDCacheInfo pc_info;
+    VTDBus *vtd_bus;
+    int bus_n, devfn;
+
+    /* PASID selective implies a DID selective */
+    pc_info.flags = VTD_PASID_CACHE_PASIDSI;
+    pc_info.domain_id = domain_id;
+    pc_info.pasid = pasid;
+
+    /*
+     * Regards to a pasid selective pasid cache invalidation (PSI),
+     * it could be either cases of below:
+     * a) a present pasid entry moved to non-present
+     * b) a present pasid entry to be a present entry
+     * c) a non-present pasid entry moved to present
+     *
+     * Here the handling of a PSI follows below steps:
+     * 1) loop all the exisitng vtd_pasid_as instances to update them
+     *    according to the latest guest pasid entry in pasid table.
+     *    this will make sure affected existing vtd_pasid_as instances
+     *    cached the latest pasid entries. Also, during the loop, the
+     *    host should be notified if needed. e.g. pasid unbind or pasid
+     *    update. Should be able to cover case a) and case b).
+     *
+     * 2) loop all devices to cover case c)
+     *    - For devices which have HostIOMMUContext instances,
+     *      we loop them and check if guest pasid entry exists. If yes,
+     *      it is case c), we update the pasid cache and also notify
+     *      host.
+     *    - For devices which have no HostIOMMUContext, it is not
+     *      necessary to create pasid cache at this phase since it
+     *      could be created when vIOMMU does DMA address translation.
+     *      This is not yet implemented since there is no emulated
+     *      pasid-capable devices today. If we have such devices in
+     *      future, the pasid cache shall be created there.
+     */
+
+    vtd_iommu_lock(s);
+    /* Step 1: loop all the exisitng vtd_pasid_as instances */
+    g_hash_table_foreach_remove(s->vtd_pasid_as,
+                                vtd_flush_pasid, &pc_info);
+
+    /* Step 1: loop all the exisitng vtd_pasid_as instances */
+    for (bus_n = 0; bus_n < PCI_BUS_MAX; bus_n++) {
+        vtd_bus = vtd_find_as_from_bus_num(s, bus_n);
+        if (!vtd_bus) {
+            continue;
+        }
+        for (devfn = 0; devfn < PCI_DEVFN_MAX; devfn++) {
+            PCIDevice *dev;
+
+            dev = vtd_bus->bus->devices[devfn];
+            if (pci_device_host_iommu_context(dev)) {
+                vtd_new_pasid_bind_for_dev(s, vtd_bus, devfn,
+                                           domain_id, pasid);
+            }
+        }
+    }
+    vtd_iommu_unlock(s);
     return 0;
 }
 
+/**
+ * Caller of this function should hold iommu_lock
+ */
+static void vtd_pasid_cache_reset(IntelIOMMUState *s)
+{
+    VTDPASIDCacheInfo pc_info;
+
+    trace_vtd_pasid_cache_reset();
+
+    pc_info.flags = VTD_PASID_CACHE_GLOBAL;
+
+    /*
+     * Reset pasid cache is a big hammer, so use
+     * g_hash_table_foreach_remove which will free
+     * the vtd_pasid_as instances, indicates the
+     * cached pasid_cache_gen would be set to 0.
+     */
+    g_hash_table_foreach_remove(s->vtd_pasid_as,
+                           vtd_flush_pasid, &pc_info);
+    s->pasid_cache_gen = 1;
+}
+
 static int vtd_pasid_cache_gsi(IntelIOMMUState *s)
 {
+    trace_vtd_pasid_cache_gsi();
+
+    vtd_iommu_lock(s);
+    s->pasid_cache_gen++;
+    if (s->pasid_cache_gen > PASID_CACHE_GEN_MAX) {
+        vtd_pasid_cache_reset(s);
+    }
+    vtd_iommu_unlock(s);
+
+    /*
+     * TODO: Global PASID cache invalidation may be
+     * flushes all the pasid caches. To be safe, after
+     * invalidating the pasid caches, emulator needs
+     * to replay the pasid bindings by walking guest
+     * pasid dir and pasid table.
+     */
     return 0;
 }
 
@@ -4052,6 +4436,8 @@  static void vtd_realize(DeviceState *dev, Error **errp)
                                      g_free, g_free);
     s->vtd_as_by_busptr = g_hash_table_new_full(vtd_uint64_hash, vtd_uint64_equal,
                                               g_free, g_free);
+    s->vtd_pasid_as = g_hash_table_new_full(vtd_pasid_as_key_hash,
+                                   vtd_pasid_as_key_equal, g_free, g_free);
     vtd_init(s);
     sysbus_mmio_map(SYS_BUS_DEVICE(s), 0, Q35_HOST_BRIDGE_IOMMU_ADDR);
     pci_setup_iommu(bus, vtd_host_dma_iommu, dev);
diff --git a/hw/i386/intel_iommu_internal.h b/hw/i386/intel_iommu_internal.h
index 0ca5f0b..2684769 100644
--- a/hw/i386/intel_iommu_internal.h
+++ b/hw/i386/intel_iommu_internal.h
@@ -307,6 +307,7 @@  typedef enum VTDFaultReason {
     VTD_FR_IR_SID_ERR = 0x26,   /* Invalid Source-ID */
 
     VTD_FR_PASID_TABLE_INV = 0x58,  /*Invalid PASID table entry */
+    VTD_FR_PASID_ENTRY_P = 0x59, /* The Present(P) field of pasidt-entry is 0 */
 
     /* This is not a normal fault reason. We use this to indicate some faults
      * that are not referenced by the VT-d specification.
@@ -481,6 +482,19 @@  struct VTDRootEntry {
 };
 typedef struct VTDRootEntry VTDRootEntry;
 
+struct VTDPASIDCacheInfo {
+#define VTD_PASID_CACHE_GLOBAL   (1ULL << 0)
+#define VTD_PASID_CACHE_DOMSI    (1ULL << 1)
+#define VTD_PASID_CACHE_PASIDSI  (1ULL << 2)
+    uint32_t flags;
+    uint16_t domain_id;
+    uint32_t pasid;
+};
+#define VTD_PASID_CACHE_INFO_MASK    (VTD_PASID_CACHE_GLOBAL | \
+                                      VTD_PASID_CACHE_DOMSI  | \
+                                      VTD_PASID_CACHE_PASIDSI)
+typedef struct VTDPASIDCacheInfo VTDPASIDCacheInfo;
+
 /* Masks for struct VTDRootEntry */
 #define VTD_ROOT_ENTRY_P            1ULL
 #define VTD_ROOT_ENTRY_CTP          (~0xfffULL)
diff --git a/hw/i386/trace-events b/hw/i386/trace-events
index f7cd4e5..87364a3 100644
--- a/hw/i386/trace-events
+++ b/hw/i386/trace-events
@@ -22,6 +22,7 @@  vtd_inv_qi_head(uint16_t head) "read head %d"
 vtd_inv_qi_tail(uint16_t head) "write tail %d"
 vtd_inv_qi_fetch(void) ""
 vtd_context_cache_reset(void) ""
+vtd_pasid_cache_reset(void) ""
 vtd_pasid_cache_gsi(void) ""
 vtd_pasid_cache_dsi(uint16_t domain) "Domian slective PC invalidation domain 0x%"PRIx16
 vtd_pasid_cache_psi(uint16_t domain, uint32_t pasid) "PASID slective PC invalidation domain 0x%"PRIx16" pasid 0x%"PRIx32
diff --git a/include/hw/i386/intel_iommu.h b/include/hw/i386/intel_iommu.h
index d8a79d3..ff41af0 100644
--- a/include/hw/i386/intel_iommu.h
+++ b/include/hw/i386/intel_iommu.h
@@ -68,6 +68,8 @@  typedef union VTD_IR_TableEntry VTD_IR_TableEntry;
 typedef union VTD_IR_MSIAddress VTD_IR_MSIAddress;
 typedef struct VTDPASIDDirEntry VTDPASIDDirEntry;
 typedef struct VTDPASIDEntry VTDPASIDEntry;
+typedef struct VTDPASIDCacheEntry VTDPASIDCacheEntry;
+typedef struct VTDPASIDAddressSpace VTDPASIDAddressSpace;
 
 /* Context-Entry */
 struct VTDContextEntry {
@@ -100,6 +102,31 @@  struct VTDPASIDEntry {
     uint64_t val[8];
 };
 
+struct pasid_key {
+    uint32_t pasid;
+    uint16_t sid;
+};
+
+struct VTDPASIDCacheEntry {
+    /*
+     * The cache entry is obsolete if
+     * pasid_cache_gen!=IntelIOMMUState.pasid_cache_gen
+     */
+    uint32_t pasid_cache_gen;
+    struct VTDPASIDEntry pasid_entry;
+};
+
+struct VTDPASIDAddressSpace {
+    VTDBus *vtd_bus;
+    uint8_t devfn;
+    AddressSpace as;
+    uint32_t pasid;
+    IntelIOMMUState *iommu_state;
+    VTDContextCacheEntry context_cache_entry;
+    QLIST_ENTRY(VTDPASIDAddressSpace) next;
+    VTDPASIDCacheEntry pasid_cache_entry;
+};
+
 struct VTDAddressSpace {
     PCIBus *bus;
     uint8_t devfn;
@@ -258,6 +285,9 @@  struct IntelIOMMUState {
 
     GHashTable *vtd_as_by_busptr;   /* VTDBus objects indexed by PCIBus* reference */
     VTDBus *vtd_as_by_bus_num[VTD_PCI_BUS_MAX]; /* VTDBus objects indexed by bus number */
+    GHashTable *vtd_pasid_as;   /* VTDPASIDAddressSpace instances */
+#define PASID_CACHE_GEN_MAX  512
+    uint32_t pasid_cache_gen;   /* Should be in [1,MAX] */
     /* list of registered notifiers */
     QLIST_HEAD(, VTDAddressSpace) vtd_as_with_notifiers;
 
@@ -277,7 +307,8 @@  struct IntelIOMMUState {
 
     /*
      * Protects IOMMU states in general.  Currently it protects the
-     * per-IOMMU IOTLB cache, and context entry cache in VTDAddressSpace.
+     * per-IOMMU IOTLB cache, and context entry cache in VTDAddressSpace,
+     * and pasid cache in VTDPASIDAddressSpace.
      */
     QemuMutex iommu_lock;
 };