> From: Peter Xu <pet...@redhat.com>
> Sent: Wednesday, March 25, 2020 1:32 AM
> To: Liu, Yi L <yi.l....@intel.com>
> Subject: Re: [PATCH v1 12/22] intel_iommu: add PASID cache management
> infrastructure
> 
> On Sun, Mar 22, 2020 at 05:36:09AM -0700, Liu Yi L wrote:
> > 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.t...@intel.com>
> > Cc: Jacob Pan <jacob.jun....@linux.intel.com>
> > Cc: Peter Xu <pet...@redhat.com>
> > Cc: Yi Sun <yi.y....@linux.intel.com>
> > Cc: Paolo Bonzini <pbonz...@redhat.com>
> > Cc: Richard Henderson <r...@twiddle.net>
> > Cc: Eduardo Habkost <ehabk...@redhat.com>
> > Signed-off-by: Liu Yi L <yi.l....@intel.com>
> > ---
> >  hw/i386/intel_iommu.c          | 394
> +++++++++++++++++++++++++++++++++++++++++
> >  hw/i386/intel_iommu_internal.h |  14 ++
> >  hw/i386/trace-events           |   1 +
> >  include/hw/i386/intel_iommu.h  |  33 +++-
> >  4 files changed, 441 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/i386/intel_iommu.c b/hw/i386/intel_iommu.c index
> > 1daeab2..c985cae 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;
> > @@ -2395,19 +2404,402 @@ 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);
> 
> The indents across the series are still strange...  Take this one as example, 
> nornally
> I'll indent at the left bracket if I want to use another newline:
> 
>        ret = vtd_get_pe_from_pasid_table(s, pasid_dir_base,
>                                          pasid, pe);
> 
> And here actually you don't need a new line at all because it's only
> 70 chars...
> 
> I don't think it's a must (I am always not sure whether we should be that 
> strict on all
> these), but it should be preferred if you change all the similar places with 
> the same
> indentation as the existing code.

Sure, I'll have a double check on it.

> > +
> > +    return ret;
> > +}
> > +
> > +static bool vtd_pasid_entry_compare(VTDPASIDEntry *p1, VTDPASIDEntry
> > +*p2) {
> > +    return !memcmp(p1, p2, sizeof(*p1)); }
> > +
> > +/**
> > + * This function cached the pasid entry in &vtd_pasid_as. Also
> > + * notifies host about the new pasid binding. Caller of this
> > + * function should hold iommu_lock.
> > + */
> > +static inline void vtd_fill_in_pe_in_cache(IntelIOMMUState *s,
> > +                                           VTDPASIDAddressSpace 
> > *vtd_pasid_as,
> > +                                           VTDPASIDEntry *pe) {
> > +    VTDPASIDCacheEntry *pc_entry = &vtd_pasid_as->pasid_cache_entry;
> > +
> > +    pc_entry->pasid_entry = *pe;
> > +    pc_entry->pasid_cache_gen = s->pasid_cache_gen;
> > +    /*
> > +     * TODO:
> > +     * - send pasid bind to host for passthru devices
> > +     */
> > +}
> > +
> > +/**
> > + * This function updates the pasid entry cached in &vtd_pasid_as.
> > + * Caller of this function should hold iommu_lock.
> > + */
> > +static void vtd_update_pe_in_cache(IntelIOMMUState *s,
> > +                                   VTDPASIDAddressSpace *vtd_pasid_as,
> > +                                   VTDPASIDEntry *pe) {
> > +    VTDPASIDCacheEntry *pc_entry = &vtd_pasid_as->pasid_cache_entry;
> > +
> > +    if (vtd_pasid_entry_compare(pe, &pc_entry->pasid_entry)) {
> > +        /* No need to go further as cached pasid entry is latest */
> > +        return;
> > +    }
> > +
> > +    vtd_fill_in_pe_in_cache(s, vtd_pasid_as, pe); }
> > +
> > +/**
> > + * 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;
> > +    }
> > +
> > +    vtd_update_pe_in_cache(s, vtd_pasid_as, &pe);
> > +    /*
> > +     * TODO:
> > +     * - when pasid-base-iotlb(piotlb) infrastructure is ready,
> > +     *   should invalidate QEMU piotlb togehter with this change.
> > +     */
> > +    return false;
> > +remove:
> > +    /*
> > +     * 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 true;
> > +}
> > +
> > +/**
> > + * 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;
> > +}
> > +
> >  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;
> >  }
> >
> >  static int vtd_pasid_cache_psi(IntelIOMMUState *s,
> >                                 uint16_t domain_id, uint32_t pasid)  {
> > +    VTDPASIDCacheInfo pc_info;
> > +    VTDHostIOMMUContext *vtd_dev_icx;
> > +
> > +    /* 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);
> > +
> 
> <START>
> 
> > +    /*
> > +     * Step 2: loop all the exisitng vtd_dev_icx instances.
> > +     * Ideally, needs to loop all devices to find if there is any new
> > +     * PASID binding regards to the PASID cache invalidation request.
> > +     * But it is enough to loop the devices which are backed by host
> > +     * IOMMU. For devices backed by vIOMMU (a.k.a emulated devices),
> > +     * if new PASID happened on them, their vtd_pasid_as instance could
> > +     * be created during future vIOMMU DMA translation.
> > +     */
> > +    QLIST_FOREACH(vtd_dev_icx, &s->vtd_dev_icx_list, next) {
> > +        VTDPASIDAddressSpace *vtd_pasid_as;
> > +        VTDPASIDCacheEntry *pc_entry;
> > +        VTDPASIDEntry pe;
> > +        VTDBus *vtd_bus = vtd_dev_icx->vtd_bus;
> > +        uint16_t devfn = vtd_dev_icx->devfn;
> > +        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);
> 
> I don't feel like it's correct here...
> 
> Assuming we have two devices assigned D1, D2.  D1 uses PASID=1, D2 uses 
> PASID=2.
> When invalidating against PASID=1, are you also going to create a
> VTDPASIDAddressSpace also for D2 with PASID=1?

Answer is no. Before going forward, let's see if the below flow looks good to 
you.

Let me add one more device besides D1 and D2. Say device D3 which also
uses PASID=1. And assume it begins with no PASID usage in guest.

Then the flow from scratch is:

a) guest IOMMU driver setup PASID entry for D1 with PASID=1,
   then invalidates against PASID #1
b) trap to QEMU, and comes to this function. Since there is
   no previous pasid cache invalidation, so the Step 1 of this
   function has nothing to do, then goes to Step 2 which is to
   loop all assigned devices and check if the guest pasid entry
   is present. In this loop, should find D1's pasid entry for
   PASID#1 is present. So create the VTDPASIDAddressSpace and
   initialize its pasid_cache_entry and pasid_cache_gen fields.
c) guest IOMMU driver setup PASID entry for D2 with PASID=2,
   then invalidates against PASID #2
d) same with b), only difference is the Step 1 of this function
   will loop the VTDPASIDAddressSpace created in b), but its
   pasid is 1 which is not the target of current pasid cache
   invalidation. Same with b), in Step 2, it will create a
   VTDPASIDAddressSpace for D2+PASID#2
e) guest IOMMU driver setup PASID entry for D3 with PASID=1,
   then invalidates against PASID #1
f) trap to QEMU and comes to this function. Step 1 loops two
   VTDPASIDAddressSpace created in b) and d), and it finds there
   is a VTDPASIDAddressSpace whose pasid is 1. vtd_flush_pasid()
   will check if the cached pasid entry is the same with the one
   in guest memory. In this flow, it should be the same, so
   vtd_flush_pasid() will do nothing for it. Then comes to Step 2,
   it loops D1, D2, D3.
   - For D1, no need to do more since there is already a
     VTDPASIDAddressSpace created for D1+PASID#1.
   - For D2, its guest pasid entry for PASID#1 is not present, so
     no need to do anything for it.
   - For D3, its guest pasid entry for PASID#1 is present and it
     is exactly the reason for this invalidation. So create a
     VTDPASIDAddressSpace for and init the pasid_cache_entry and
     pasid_cache_gen fields.

> I feel like we shouldn't create VTDPASIDAddressSpace only if it existed, say, 
> until
> when we reach vtd_dev_get_pe_from_pasid() below with retcode==0.

You are right. I think I failed to destroy the VTDAddressSpace when
vtd_dev_get_pe_from_pasid() returns error. Thus the code won't create
a VTDPASIDAddressSpace for D2+PASID#1.

> Besides this...
> 
> > +        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 in Step 1. Thus no need for the below steps.
> > +             */
> > +            continue;
> > +        }
> > +
> > +        /*
> > +         * 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)) {

Yi: should destroy pasid_as as there is no valid pasid entry. Thus to
ensure all the pasid_as in hash table are valid.

> > +            continue;
> > +        }
> > +
> > +        /*
> > +         * 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_in_cache(s, vtd_pasid_as, &pe);
> > +        }
> > +    }
> 
> <END>
> 
> ... I'm a bit confused on the whole range between <START> and <END> on how it
> differs from the vtd_replay_guest_pasid_bindings() you're going to introduce.
> Shouldn't the replay code do similar thing?  Can we merge them?

Yes, there is similar thing which is to create VTDPASIDAddressSpace
per the guest pasid entry presence.

But there are differences. For one, the code here is to loop all
assigned devices for a specific PASID. While the logic in
vtd_replay_guest_pasid_bindings() is to loop all assigned devices
and the PASID tables behind them. For two, the code here only cares
about the case which guest pasid entry from INVALID->VALID.
The reason is in Step 1 of this function, VALID->INVALID and
VALID->VALID cases are already covered. While the logic in
vtd_replay_guest_pasid_bindings() needs to cover all the three cases.
The last reason I didn't merge them is in vtd_replay_guest_pasid_bindings()
it needs to divide the pasid entry fetch into two steps and check
the result (if fetch pasid directory entry failed, it could skip a
range of PASIDs). While the code in this function, it doesn't care
about it, it only cares if there is a valid pasid entry for this
specific pasid.

> 
> My understanding is that we can just make sure to do it right once in the 
> replay
> code (the three cases: INVALID->VALID, VALID->INVALID,
> VALID->VALID), then no matter whether it's DSI/PSI/GSI, we call the
> replay code probably with VTDPASIDCacheInfo* passed in, then the replay code 
> will
> know what to look after.

Hmmm, let me think more to abstract the code between the
<START> and <END> to be a helper function to be called by
vtd_replay_guest_pasid_bindings(). Also, in that case, I
need to apply the two step concept in the replay function.

> > +
> > +    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);
> 
> Would this make sure the per pasid_as pasid_cache_gen will be reset to zero?  
> I'm
> not very sure, say, what if the memory is stall during a reset and still have 
> the old
> data?
> 
> I'm not sure, but I feel like we should simply drop all pasid_as here, rather 
> than
> using the same code for a global pasid invalidation.

I see. Maybe I can get another helper function which always returns
true, and replace vtd_flush_pasid with the new function. This should
ensure all pasid_as are dropped. How do you think?

Regards,
Yi Liu

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