Re: [Qemu-ppc] [PATCHv3 3/5] pseries: Implement HPT resizing

[David Gibson]

On Wed, Dec 14, 2016 at 04:30:57PM +1100, Suraj Jitindar Singh wrote:
> On Mon, 2016-12-12 at 15:06 +1100, David Gibson wrote:
> > This patch implements hypercalls allowing a PAPR guest to resize its
> > own
> > hash page table.  This will eventually allow for more flexible memory
> > hotplug.
> > 
> > The implementation is partially asynchronous, handled in a special
> > thread
> > running the hpt_prepare_thread() function.  The state of a pending
> > resize
> > is stored in SPAPR_MACHINE->pending_hpt.
> > 
> > The H_RESIZE_HPT_PREPARE hypercall will kick off creation of a new
> > HPT, or,
> > if one is already in progress, monitor it for completion.  If there
> > is an
> > existing HPT resize in progress that doesn't match the size specified
> > in
> > the call, it will cancel it, replacing it with a new one matching the
> > given size.
> > 
> > The H_RESIZE_HPT_COMMIT completes transition to a resized HPT, and
> > can only
> > be called successfully once H_RESIZE_HPT_PREPARE has successfully
> > completed initialization of a new HPT.  The guest must ensure that
> > there
> > are no concurrent accesses to the existing HPT while this is called
> > (this
> > effectively means stop_machine() for Linux guests).
> > 
> > For now H_RESIZE_HPT_COMMIT goes through the whole old HPT, rehashing
> > each
> > HPTE into the new HPT.  This can have quite high latency, but it
> > seems to
> > be of the order of typical migration downtime latencies for HPTs of
> > size
> > up to ~2GiB (which would be used in a 256GiB guest).
> > 
> > In future we probably want to move more of the rehashing to the
> > "prepare"
> > phase, by having H_ENTER and other hcalls update both current and
> > pending HPTs.  That's a project for another day, but should be
> > possible
> > without any changes to the guest interface.
> > 
> > Signed-off-by: David Gibson <address@hidden>
> > ---
> >  hw/ppc/spapr.c          |   4 +-
> >  hw/ppc/spapr_hcall.c    | 345
> > +++++++++++++++++++++++++++++++++++++++++++++++-
> >  include/hw/ppc/spapr.h  |   6 +
> >  target-ppc/mmu-hash64.h |   4 +
> >  4 files changed, 353 insertions(+), 6 deletions(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 846ce51..d057031 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -93,8 +93,6 @@
> >  
> >  #define PHANDLE_XICP            0x00001111
> >  
> > -#define HTAB_SIZE(spapr)        (1ULL << ((spapr)->htab_shift))
> > -
> >  static XICSState *try_create_xics(const char *type, int nr_servers,
> >                                    int nr_irqs, Error **errp)
> >  {
> > @@ -1055,7 +1053,7 @@ static void close_htab_fd(sPAPRMachineState
> > *spapr)
> >      spapr->htab_fd = -1;
> >  }
> >  
> > -static int spapr_hpt_shift_for_ramsize(uint64_t ramsize)
> > +int spapr_hpt_shift_for_ramsize(uint64_t ramsize)
> >  {
> >      int shift;
> >  
> > diff --git a/hw/ppc/spapr_hcall.c b/hw/ppc/spapr_hcall.c
> > index 72a9c4d..1e89061 100644
> > --- a/hw/ppc/spapr_hcall.c
> > +++ b/hw/ppc/spapr_hcall.c
> > @@ -2,6 +2,7 @@
> >  #include "qapi/error.h"
> >  #include "sysemu/sysemu.h"
> >  #include "qemu/log.h"
> > +#include "qemu/error-report.h"
> >  #include "cpu.h"
> >  #include "exec/exec-all.h"
> >  #include "helper_regs.h"
> > @@ -355,20 +356,319 @@ static target_ulong h_read(PowerPCCPU *cpu,
> > sPAPRMachineState *spapr,
> >      return H_SUCCESS;
> >  }
> >  
> > +struct sPAPRPendingHPT {
> > +    /* These fields are read-only after initialization */
> > +    int shift;
> > +    QemuThread thread;
> > +
> > +    /* These fields are protected by the BQL */
> > +    bool complete;
> > +
> > +    /* These fields are private to the preparation thread if
> > +     * !complete, otherwise protected by the BQL */
> > +    int ret;
> > +    void *hpt;
> > +};
> > +
> > +static void free_pending_hpt(sPAPRPendingHPT *pending)
> > +{
> > +    if (pending->hpt) {
> > +        qemu_vfree(pending->hpt);
> > +    }
> > +
> > +    g_free(pending);
> > +}
> > +
> > +static void *hpt_prepare_thread(void *opaque)
> > +{
> > +    sPAPRPendingHPT *pending = opaque;
> > +    size_t size = 1ULL << pending->shift;
> > +
> > +    pending->hpt = qemu_memalign(size, size);
> > +    if (pending->hpt) {
> > +        memset(pending->hpt, 0, size);
> > +        pending->ret = H_SUCCESS;
> > +    } else {
> > +        pending->ret = H_NO_MEM;
> > +    }
> > +
> > +    qemu_mutex_lock_iothread();
> > +
> > +    if (SPAPR_MACHINE(qdev_get_machine())->pending_hpt == pending) {
> > +        /* Ready to go */
> > +        pending->complete = true;
> > +    } else {
> > +        /* We've been cancelled, clean ourselves up */
> > +        free_pending_hpt(pending);
> > +    }
> > +
> > +    qemu_mutex_unlock_iothread();
> > +    return NULL;
> > +}
> > +
> > +/* Must be called with BQL held */
> > +static void cancel_hpt_prepare(sPAPRMachineState *spapr)
> > +{
> > +    sPAPRPendingHPT *pending = spapr->pending_hpt;
> > +
> > +    /* Let the thread know it's cancelled */
> > +    spapr->pending_hpt = NULL;
> > +
> > +    if (!pending) {
> > +        /* Nothing to do */
> > +        return;
> > +    }
> > +
> > +    if (!pending->complete) {
> > +        /* thread will clean itself up */
> > +        return;
> > +    }
> > +
> > +    free_pending_hpt(pending);
> > +}
> > +
> > +static int build_dimm_list(Object *obj, void *opaque)
> > +{
> > +    GSList **list = opaque;
> > +
> > +    if (object_dynamic_cast(obj, TYPE_PC_DIMM)) {
> > +        DeviceState *dev = DEVICE(obj);
> > +        if (dev->realized) { /* only realized DIMMs matter */
> > +            *list = g_slist_prepend(*list, dev);
> > +        }
> > +    }
> > +
> > +    object_child_foreach(obj, build_dimm_list, opaque);
> > +    return 0;
> > +}
> > +
> > +static ram_addr_t get_current_ram_size(void)
> > +{
> > +    GSList *list = NULL, *item;
> > +    ram_addr_t size = ram_size;
> > +
> > +    build_dimm_list(qdev_get_machine(), &list);
> > +    for (item = list; item; item = g_slist_next(item)) {
> > +        Object *obj = OBJECT(item->data);
> > +        if (!strcmp(object_get_typename(obj), TYPE_PC_DIMM)) {
> > +            size += object_property_get_int(obj, PC_DIMM_SIZE_PROP,
> > +                                            &error_abort);
> > +        }
> > +    }
> > +    g_slist_free(list);
> > +
> > +    return size;
> > +}
> > +
> >  static target_ulong h_resize_hpt_prepare(PowerPCCPU *cpu,
> >                                           sPAPRMachineState *spapr,
> >                                           target_ulong opcode,
> >                                           target_ulong *args)
> >  {
> >      target_ulong flags = args[0];
> > -    target_ulong shift = args[1];
> > +    int shift = args[1];
> > +    sPAPRPendingHPT *pending = spapr->pending_hpt;
> >  
> >      if (spapr->resize_hpt == SPAPR_RESIZE_HPT_DISABLED) {
> >          return H_AUTHORITY;
> >      }
> >  
> >      trace_spapr_h_resize_hpt_prepare(flags, shift);
> > -    return H_HARDWARE;
> > +
> > +    if (flags != 0) {
> > +        return H_PARAMETER;
> > +    }
> > +
> > +    if (shift && ((shift < 18) || (shift > 46))) {
> > +        return H_PARAMETER;
> > +    }
> > +
> > +    if (pending) {
> > +        /* something already in progress */
> > +        if (pending->shift == shift) {
> > +            /* and it's suitable */
> > +            if (pending->complete) {
> > +                return pending->ret;
> > +            } else {
> > +                return H_LONG_BUSY_ORDER_100_MSEC;
> > +            }
> > +        }
> > +
> > +        /* not suitable, cancel and replace */
> > +        cancel_hpt_prepare(spapr);
> > +    }
> > +
> > +    if (!shift) {
> > +        /* nothing to do */
> > +        return H_SUCCESS;
> > +    }
> > +
> > +    /* start new prepare */
> > +
> > +    /* We only allow the guest to allocate an HPT one order above
> > what
> > +     * we'd normally give them (to stop a small guest claiming a
> > huge
> > +     * chunk of resources in the HPT */
> > +    if (shift > (spapr_hpt_shift_for_ramsize(get_current_ram_size())
> > + 1)) {
> > +        return H_RESOURCE;
> > +    }
> > +
> > +    pending = g_new0(sPAPRPendingHPT, 1);
> > +    pending->shift = shift;
> > +    pending->ret = H_HARDWARE;
> > +
> > +    qemu_thread_create(&pending->thread, "sPAPR HPT prepare",
> > +                       hpt_prepare_thread, pending,
> > QEMU_THREAD_DETACHED);
> > +
> > +    spapr->pending_hpt = pending;
> > +
> > +    /* In theory we could estimate the time more accurately based on
> > +     * the new size, but there's not much point */
> > +    return H_LONG_BUSY_ORDER_100_MSEC;
> > +}
> > +
> > +static uint64_t new_hpte_load0(void *htab, uint64_t pteg, int slot)
> > +{
> > +    uint8_t *addr = htab;
> > +
> > +    addr += pteg * HASH_PTEG_SIZE_64;
> > +    addr += slot * HASH_PTE_SIZE_64;
> > +    return  ldq_p(addr);
> > +}
> > +
> > +static void new_hpte_store(void *htab, uint64_t pteg, int slot,
> > +                           uint64_t pte0, uint64_t pte1)
> > +{
> > +    uint8_t *addr = htab;
> > +
> > +    addr += pteg * HASH_PTEG_SIZE_64;
> > +    addr += slot * HASH_PTE_SIZE_64;
> > +
> > +    stq_p(addr, pte0);
> > +    stq_p(addr + HASH_PTE_SIZE_64/2, pte1);
> > +}
> > +
> > +static int rehash_hpte(PowerPCCPU *cpu, uint64_t token,
> > +                       void *old, uint64_t oldsize,
> > +                       void *new, uint64_t newsize,
> Can we call these old_hpt and new_hpt?

Done.

> > +                       uint64_t pteg, int slot)
> > +{
> > +    uint64_t old_hash_mask = (oldsize >> 7) - 1;
> > +    uint64_t new_hash_mask = (newsize >> 7) - 1;
> > +    target_ulong pte0 = ppc_hash64_load_hpte0(cpu, token, slot);
> > +    target_ulong pte1;
> > +    uint64_t avpn;
> > +    unsigned shift;
> Can we call this base_pg_shift or at least add a comment:
> /* Base Virtual Page Shift */ or something?
> Took me a while to work out what *shift* this actually was...

Ah, good point.  Especially since I usually use 'shift' to refer to
the whole HPT size.  Changed.

> > +    uint64_t hash, new_pteg, replace_pte0;
> > +
> *** (referenced below)
> > +    if (!(pte0 & HPTE64_V_VALID) || !(pte0 & HPTE64_V_BOLTED)) {
> > +        return H_SUCCESS;
> > +    }
> > +
> > +    pte1 = ppc_hash64_load_hpte1(cpu, token, slot);
> > +
> > +    shift = ppc_hash64_hpte_page_shift_noslb(cpu, pte0, pte1);
> > +    assert(shift); /* H_ENTER should never have allowed a bad
> > encoding */
> > +    avpn = HPTE64_V_AVPN_VAL(pte0) & ~(((1ULL << shift) - 1) >> 23);
> > +
> > +    if (pte0 & HPTE64_V_SECONDARY) {
> > +        pteg = ~pteg;
> > +    }
> > +
> The hash calculation below is pretty hard to follow... That being said
> I don't really see a nicer way of structuring it. I guess you just have
> to wade through the ISA if you actually want to understand what's
> happening here (which I assume most people won't bother with).
> > +    if ((pte0 & HPTE64_V_SSIZE) == HPTE64_V_SSIZE_256M) {
> > +        uint64_t offset, vsid;
> > +
> > +        /* We only have 28 - 23 bits of offset in avpn */
> > +        offset = (avpn & 0x1f) << 23;
> > +        vsid = avpn >> 5;
> > +        /* We can find more bits from the pteg value */
> > +        if (shift < 23) {
> > +            offset |= ((vsid ^ pteg) & old_hash_mask) << shift;
> > +        }
> > +
> > +        hash = vsid ^ (offset >> shift);
> > +    } else if ((pte0 & HPTE64_V_SSIZE) == HPTE64_V_SSIZE_1T) {
> > +        uint64_t offset, vsid;
> > +
> > +        /* We only have 40 - 23 bits of seg_off in avpn */
> > +        offset = (avpn & 0x1ffff) << 23;
> > +        vsid = avpn >> 17;
> > +        if (shift < 23) {
> > +            offset |= ((vsid ^ (vsid << 25) ^ pteg) & old_hash_mask)
> > << shift;
> > +        }
> > +
> > +        hash = vsid ^ (vsid << 25) ^ (offset >> shift);
> > +    } else {
> > +        error_report("rehash_pte: Bad segment size in HPTE");
> > +        return H_HARDWARE;
> > +    }
> > +
> > +    new_pteg = hash & new_hash_mask;
> > +    if (pte0 & HPTE64_V_SECONDARY) {
> > +        assert(~pteg == (hash & old_hash_mask));
> > +        new_pteg = ~new_pteg;
> > +    } else {
> > +        assert(pteg == (hash & old_hash_mask));
> > +    }
> > +    assert((oldsize != newsize) || (pteg == new_pteg));
> > +    replace_pte0 = new_hpte_load0(new, new_pteg, slot);
> > +    if (replace_pte0 & HPTE64_V_VALID) {
> > +        assert(newsize < oldsize);
> > +        if (replace_pte0 & HPTE64_V_BOLTED) {
> Aren't both of these checks for BOLTED redundant? We know that we are
> only rehashing ptes which are both valid and bolted, otherwise we would
> have returned at *** above. Thus the new hpt will only contain invalid
> entries or valid && bolted entries, we don't need to check if
> replace_pte is bolted if we know it's valid. Similarly we know the one
> we are replacing it with is bolted, otherwise we wouldn't have bothered
> rehashing it. Thus it's pretty much sufficient to check replace_pte0
> && HPTE64_V_VALID == 1 which implies a bolted collision irrespective.

I've added a comment explaining why this code is here.

> > +            if (pte0 & HPTE64_V_BOLTED) {
> > +                /* Bolted collision, nothing we can do */
> > +                return H_PTEG_FULL;
> > +            } else {
> > +                /* Discard this hpte */
> > +                return H_SUCCESS;
> > +            }
> > +        }
> Is there any reason the rehashed pte has to go into the same slot it
> came out of? Isn't it valid to search all of the slots of the new pteg
> for an empty (invalid) one and put it in the first empty space? Just
> because the current slot already contains a bolted entry doesn't mean
> we can't put it in another slot, right?
> > +    }
> > +
> > +    new_hpte_store(new, new_pteg, slot, pte0, pte1);
> > +    return H_SUCCESS;
> > +}
> > +
> > +static int rehash_hpt(PowerPCCPU *cpu,
> > +                      void *old, uint64_t oldsize,
> > +                      void *new, uint64_t newsize)
> > +{
> > +    CPUPPCState *env = &cpu->env;
> > +    uint64_t n_ptegs = oldsize >> 7;
> > +    uint64_t pteg;
> > +    int slot;
> > +    int rc;
> > +
> > +    assert(env->external_htab == old);
> > +
> > +    for (pteg = 0; pteg < n_ptegs; pteg++) {
> Can we rename token to pteg_[base_]addr or something? Token is very...
> generic
> > +        uint64_t token = ppc_hash64_start_access(cpu, pteg *
> > HPTES_PER_GROUP);
> > +
> > +        if (!token) {
> > +            return H_HARDWARE;
> > +        }
> > +
> > +        for (slot = 0; slot < HPTES_PER_GROUP; slot++) {
> > +            rc = rehash_hpte(cpu, token, old, oldsize, new, newsize,
> > +                             pteg, slot);
> > +            if (rc != H_SUCCESS) {
> > +                ppc_hash64_stop_access(cpu, token);
> > +                return rc;
> > +            }
> > +        }
> > +        ppc_hash64_stop_access(cpu, token);
> > +    }
> > +
> > +    return H_SUCCESS;
> > +}
> > +
> > +static void pivot_hpt(CPUState *cs, run_on_cpu_data arg)
> > +{
> > +    sPAPRMachineState *spapr = SPAPR_MACHINE(arg.host_ptr);
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +
> > +    cpu_synchronize_state(cs);
> > +    ppc_hash64_set_external_hpt(cpu, spapr->htab, spapr->htab_shift,
> > +                                &error_fatal);
> >  }
> >  
> >  static target_ulong h_resize_hpt_commit(PowerPCCPU *cpu,
> > @@ -378,13 +678,52 @@ static target_ulong
> > h_resize_hpt_commit(PowerPCCPU *cpu,
> >  {
> >      target_ulong flags = args[0];
> >      target_ulong shift = args[1];
> > +    sPAPRPendingHPT *pending = spapr->pending_hpt;
> > +    int rc;
> > +    size_t newsize;
> >  
> >      if (spapr->resize_hpt == SPAPR_RESIZE_HPT_DISABLED) {
> >          return H_AUTHORITY;
> >      }
> >  
> >      trace_spapr_h_resize_hpt_commit(flags, shift);
> > -    return H_HARDWARE;
> > +
> > +    if (flags != 0) {
> > +        return H_PARAMETER;
> > +    }
> > +
> > +    if (!pending || (pending->shift != shift)) {
> > +        /* no matching prepare */
> > +        return H_CLOSED;
> > +    }
> > +
> > +    if (!pending->complete) {
> > +        /* prepare has not completed */
> > +        return H_BUSY;
> > +    }
> > +
> > +    newsize = 1ULL << pending->shift;
> > +    rc = rehash_hpt(cpu, spapr->htab, HTAB_SIZE(spapr),
> > +                    pending->hpt, newsize);
> > +    if (rc == H_SUCCESS) {
> > +        CPUState *cs;
> > +
> > +        qemu_vfree(spapr->htab);
> > +        spapr->htab = pending->hpt;
> > +        spapr->htab_shift = pending->shift;
> > +
> > +        CPU_FOREACH(cs) {
> > +            run_on_cpu(cs, pivot_hpt, RUN_ON_CPU_HOST_PTR(spapr));
> > +        }
> > +
> > +        pending->hpt = NULL; /* so it's not free()d */
> > +    }
> > +
> > +    /* Clean up */
> > +    spapr->pending_hpt = NULL;
> > +    free_pending_hpt(pending);
> > +
> > +    return rc;
> >  }
> >  
> >  static target_ulong h_set_sprg0(PowerPCCPU *cpu, sPAPRMachineState
> > *spapr,
> > diff --git a/include/hw/ppc/spapr.h b/include/hw/ppc/spapr.h
> > index d2c758b..954bada 100644
> > --- a/include/hw/ppc/spapr.h
> > +++ b/include/hw/ppc/spapr.h
> > @@ -14,6 +14,7 @@ struct sPAPRNVRAM;
> >  typedef struct sPAPRConfigureConnectorState
> > sPAPRConfigureConnectorState;
> >  typedef struct sPAPREventLogEntry sPAPREventLogEntry;
> >  typedef struct sPAPREventSource sPAPREventSource;
> > +typedef struct sPAPRPendingHPT sPAPRPendingHPT;
> >  
> >  #define HPTE64_V_HPTE_DIRTY     0x0000000000000040ULL
> >  #define SPAPR_ENTRY_POINT       0x100
> > @@ -72,6 +73,8 @@ struct sPAPRMachineState {
> >      sPAPRResizeHPT resize_hpt;
> >      void *htab;
> >      uint32_t htab_shift;
> > +    sPAPRPendingHPT *pending_hpt; /* in-progress resize */
> > +
> >      hwaddr rma_size;
> >      int vrma_adjust;
> >      ssize_t rtas_size;
> > @@ -627,6 +630,7 @@ void
> > spapr_hotplug_req_remove_by_count_indexed(sPAPRDRConnectorType
> > drc_type,
> >                                                 uint32_t count,
> > uint32_t index);
> >  void *spapr_populate_hotplug_cpu_dt(CPUState *cs, int *fdt_offset,
> >                                      sPAPRMachineState *spapr);
> > +int spapr_hpt_shift_for_ramsize(uint64_t ramsize);
> >  
> >  /* rtas-configure-connector state */
> >  struct sPAPRConfigureConnectorState {
> > @@ -674,4 +678,6 @@ int spapr_rng_populate_dt(void *fdt);
> >  
> >  void spapr_do_system_reset_on_cpu(CPUState *cs, run_on_cpu_data
> > arg);
> >  
> > +#define HTAB_SIZE(spapr)        (1ULL << ((spapr)->htab_shift))
> > +
> >  #endif /* HW_SPAPR_H */
> > diff --git a/target-ppc/mmu-hash64.h b/target-ppc/mmu-hash64.h
> > index ab5d347..4a1b781 100644
> > --- a/target-ppc/mmu-hash64.h
> > +++ b/target-ppc/mmu-hash64.h
> > @@ -60,11 +60,15 @@ void ppc_hash64_update_rmls(CPUPPCState *env);
> >  #define HASH_PTE_SIZE_64        16
> >  #define HASH_PTEG_SIZE_64       (HASH_PTE_SIZE_64 * HPTES_PER_GROUP)
> >  
> > +#define HPTE64_V_SSIZE          SLB_VSID_B
> > +#define HPTE64_V_SSIZE_256M     SLB_VSID_B_256M
> > +#define HPTE64_V_SSIZE_1T       SLB_VSID_B_1T
> >  #define HPTE64_V_SSIZE_SHIFT    62
> >  #define HPTE64_V_AVPN_SHIFT     7
> >  #define HPTE64_V_AVPN           0x3fffffffffffff80ULL
> >  #define HPTE64_V_AVPN_VAL(x)    (((x) & HPTE64_V_AVPN) >>
> > HPTE64_V_AVPN_SHIFT)
> >  #define HPTE64_V_COMPARE(x, y)  (!(((x) ^ (y)) &
> > 0xffffffffffffff83ULL))
> > +#define HPTE64_V_BOLTED         0x0000000000000010ULL
> >  #define HPTE64_V_LARGE          0x0000000000000004ULL
> >  #define HPTE64_V_SECONDARY      0x0000000000000002ULL
> >  #define HPTE64_V_VALID          0x0000000000000001ULL
> 

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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