Re: [Qemu-devel] [PATCH v7 2/3] tcg: introduce dynamic TLB sizing

["Alex Bennée" <alex.bennee@linaro.org>]

Emilio G. Cota <cota@braap.org> writes:

> Disabled in all TCG backends for now.
>
> Signed-off-by: Emilio G. Cota <cota@braap.org>

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>

> ---
>  include/exec/cpu-defs.h  |  57 ++++++++++-
>  include/exec/cpu_ldst.h  |  21 ++++
>  tcg/aarch64/tcg-target.h |   1 +
>  tcg/arm/tcg-target.h     |   1 +
>  tcg/i386/tcg-target.h    |   1 +
>  tcg/mips/tcg-target.h    |   1 +
>  tcg/ppc/tcg-target.h     |   1 +
>  tcg/riscv/tcg-target.h   |   1 +
>  tcg/s390/tcg-target.h    |   1 +
>  tcg/sparc/tcg-target.h   |   1 +
>  tcg/tci/tcg-target.h     |   1 +
>  accel/tcg/cputlb.c       | 202 ++++++++++++++++++++++++++++++++++++++-
>  12 files changed, 282 insertions(+), 7 deletions(-)
>
> diff --git a/include/exec/cpu-defs.h b/include/exec/cpu-defs.h
> index 6a60f94a41..191a1e021f 100644
> --- a/include/exec/cpu-defs.h
> +++ b/include/exec/cpu-defs.h
> @@ -67,6 +67,28 @@ typedef uint64_t target_ulong;
>  #define CPU_TLB_ENTRY_BITS 5
>  #endif
>
> +#if TCG_TARGET_IMPLEMENTS_DYN_TLB
> +#define CPU_TLB_DYN_MIN_BITS 6
> +#define CPU_TLB_DYN_DEFAULT_BITS 8
> +
> +
> +# if HOST_LONG_BITS == 32
> +/* Make sure we do not require a double-word shift for the TLB load */
> +#  define CPU_TLB_DYN_MAX_BITS (32 - TARGET_PAGE_BITS)
> +# else /* HOST_LONG_BITS == 64 */
> +/*
> + * Assuming TARGET_PAGE_BITS==12, with 2**22 entries we can cover 2**(22+12) ==
> + * 2**34 == 16G of address space. This is roughly what one would expect a
> + * TLB to cover in a modern (as of 2018) x86_64 CPU. For instance, Intel
> + * Skylake's Level-2 STLB has 16 1G entries.
> + * Also, make sure we do not size the TLB past the guest's address space.
> + */
> +#  define CPU_TLB_DYN_MAX_BITS                                  \
> +    MIN(22, TARGET_VIRT_ADDR_SPACE_BITS - TARGET_PAGE_BITS)
> +# endif
> +
> +#else /* !TCG_TARGET_IMPLEMENTS_DYN_TLB */
> +
>  /* TCG_TARGET_TLB_DISPLACEMENT_BITS is used in CPU_TLB_BITS to ensure that
>   * the TLB is not unnecessarily small, but still small enough for the
>   * TLB lookup instruction sequence used by the TCG target.
> @@ -98,6 +120,7 @@ typedef uint64_t target_ulong;
>           NB_MMU_MODES <= 8 ? 3 : 4))
>
>  #define CPU_TLB_SIZE (1 << CPU_TLB_BITS)
> +#endif /* TCG_TARGET_IMPLEMENTS_DYN_TLB */
>
>  typedef struct CPUTLBEntry {
>      /* bit TARGET_LONG_BITS to TARGET_PAGE_BITS : virtual address
> @@ -141,6 +164,18 @@ typedef struct CPUIOTLBEntry {
>      MemTxAttrs attrs;
>  } CPUIOTLBEntry;
>
> +/**
> + * struct CPUTLBWindow
> + * @begin_ns: host time (in ns) at the beginning of the time window
> + * @max_entries: maximum number of entries observed in the window
> + *
> + * See also: tlb_mmu_resize_locked()
> + */
> +typedef struct CPUTLBWindow {
> +    int64_t begin_ns;
> +    size_t max_entries;
> +} CPUTLBWindow;
> +
>  typedef struct CPUTLBDesc {
>      /*
>       * Describe a region covering all of the large pages allocated
> @@ -152,6 +187,10 @@ typedef struct CPUTLBDesc {
>      target_ulong large_page_mask;
>      /* The next index to use in the tlb victim table.  */
>      size_t vindex;
> +#if TCG_TARGET_IMPLEMENTS_DYN_TLB
> +    CPUTLBWindow window;
> +    size_t n_used_entries;
> +#endif
>  } CPUTLBDesc;
>
>  /*
> @@ -176,6 +215,20 @@ typedef struct CPUTLBCommon {
>      size_t elide_flush_count;
>  } CPUTLBCommon;
>
> +#if TCG_TARGET_IMPLEMENTS_DYN_TLB
> +# define CPU_TLB                                                        \
> +    /* tlb_mask[i] contains (n_entries - 1) << CPU_TLB_ENTRY_BITS */    \
> +    uintptr_t tlb_mask[NB_MMU_MODES];                                   \
> +    CPUTLBEntry *tlb_table[NB_MMU_MODES];
> +# define CPU_IOTLB                              \
> +    CPUIOTLBEntry *iotlb[NB_MMU_MODES];
> +#else
> +# define CPU_TLB                                        \
> +    CPUTLBEntry tlb_table[NB_MMU_MODES][CPU_TLB_SIZE];
> +# define CPU_IOTLB                                      \
> +    CPUIOTLBEntry iotlb[NB_MMU_MODES][CPU_TLB_SIZE];
> +#endif
> +
>  /*
>   * The meaning of each of the MMU modes is defined in the target code.
>   * Note that NB_MMU_MODES is not yet defined; we can only reference it
> @@ -184,9 +237,9 @@ typedef struct CPUTLBCommon {
>  #define CPU_COMMON_TLB \
>      CPUTLBCommon tlb_c;                                                 \
>      CPUTLBDesc tlb_d[NB_MMU_MODES];                                     \
> -    CPUTLBEntry tlb_table[NB_MMU_MODES][CPU_TLB_SIZE];                  \
> +    CPU_TLB                                                             \
>      CPUTLBEntry tlb_v_table[NB_MMU_MODES][CPU_VTLB_SIZE];               \
> -    CPUIOTLBEntry iotlb[NB_MMU_MODES][CPU_TLB_SIZE];                    \
> +    CPU_IOTLB                                                           \
>      CPUIOTLBEntry iotlb_v[NB_MMU_MODES][CPU_VTLB_SIZE];
>
>  #else
> diff --git a/include/exec/cpu_ldst.h b/include/exec/cpu_ldst.h
> index 959068495a..83b2907d86 100644
> --- a/include/exec/cpu_ldst.h
> +++ b/include/exec/cpu_ldst.h
> @@ -135,6 +135,21 @@ static inline target_ulong tlb_addr_write(const CPUTLBEntry *entry)
>  #endif
>  }
>
> +#if TCG_TARGET_IMPLEMENTS_DYN_TLB
> +/* Find the TLB index corresponding to the mmu_idx + address pair.  */
> +static inline uintptr_t tlb_index(CPUArchState *env, uintptr_t mmu_idx,
> +                                  target_ulong addr)
> +{
> +    uintptr_t size_mask = env->tlb_mask[mmu_idx] >> CPU_TLB_ENTRY_BITS;
> +
> +    return (addr >> TARGET_PAGE_BITS) & size_mask;
> +}
> +
> +static inline size_t tlb_n_entries(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +    return (env->tlb_mask[mmu_idx] >> CPU_TLB_ENTRY_BITS) + 1;
> +}
> +#else
>  /* Find the TLB index corresponding to the mmu_idx + address pair.  */
>  static inline uintptr_t tlb_index(CPUArchState *env, uintptr_t mmu_idx,
>                                    target_ulong addr)
> @@ -142,6 +157,12 @@ static inline uintptr_t tlb_index(CPUArchState *env, uintptr_t mmu_idx,
>      return (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
>  }
>
> +static inline size_t tlb_n_entries(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +    return CPU_TLB_SIZE;
> +}
> +#endif /* TCG_TARGET_IMPLEMENTS_DYN_TLB */
> +
>  /* Find the TLB entry corresponding to the mmu_idx + address pair.  */
>  static inline CPUTLBEntry *tlb_entry(CPUArchState *env, uintptr_t mmu_idx,
>                                       target_ulong addr)
> diff --git a/tcg/aarch64/tcg-target.h b/tcg/aarch64/tcg-target.h
> index f966a4fcb3..bff91c5aa0 100644
> --- a/tcg/aarch64/tcg-target.h
> +++ b/tcg/aarch64/tcg-target.h
> @@ -15,6 +15,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE  4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 24
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>  #undef TCG_TARGET_STACK_GROWSUP
>
>  typedef enum {
> diff --git a/tcg/arm/tcg-target.h b/tcg/arm/tcg-target.h
> index 16172f73a3..c5a7064bdc 100644
> --- a/tcg/arm/tcg-target.h
> +++ b/tcg/arm/tcg-target.h
> @@ -60,6 +60,7 @@ extern int arm_arch;
>  #undef TCG_TARGET_STACK_GROWSUP
>  #define TCG_TARGET_INSN_UNIT_SIZE 4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 16
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>
>  typedef enum {
>      TCG_REG_R0 = 0,
> diff --git a/tcg/i386/tcg-target.h b/tcg/i386/tcg-target.h
> index f378d29568..bd7d37c7ef 100644
> --- a/tcg/i386/tcg-target.h
> +++ b/tcg/i386/tcg-target.h
> @@ -27,6 +27,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE  1
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 31
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>
>  #ifdef __x86_64__
>  # define TCG_TARGET_REG_BITS  64
> diff --git a/tcg/mips/tcg-target.h b/tcg/mips/tcg-target.h
> index 5cb8672470..8600eefd9a 100644
> --- a/tcg/mips/tcg-target.h
> +++ b/tcg/mips/tcg-target.h
> @@ -37,6 +37,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE 4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 16
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>  #define TCG_TARGET_NB_REGS 32
>
>  typedef enum {
> diff --git a/tcg/ppc/tcg-target.h b/tcg/ppc/tcg-target.h
> index 52c1bb04b1..b51854b5cf 100644
> --- a/tcg/ppc/tcg-target.h
> +++ b/tcg/ppc/tcg-target.h
> @@ -34,6 +34,7 @@
>  #define TCG_TARGET_NB_REGS 32
>  #define TCG_TARGET_INSN_UNIT_SIZE 4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 16
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>
>  typedef enum {
>      TCG_REG_R0,  TCG_REG_R1,  TCG_REG_R2,  TCG_REG_R3,
> diff --git a/tcg/riscv/tcg-target.h b/tcg/riscv/tcg-target.h
> index 60918cacb4..1eb032626c 100644
> --- a/tcg/riscv/tcg-target.h
> +++ b/tcg/riscv/tcg-target.h
> @@ -33,6 +33,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE 4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 20
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>  #define TCG_TARGET_NB_REGS 32
>
>  typedef enum {
> diff --git a/tcg/s390/tcg-target.h b/tcg/s390/tcg-target.h
> index 853ed6e7aa..394b545369 100644
> --- a/tcg/s390/tcg-target.h
> +++ b/tcg/s390/tcg-target.h
> @@ -27,6 +27,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE 2
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 19
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>
>  typedef enum TCGReg {
>      TCG_REG_R0 = 0,
> diff --git a/tcg/sparc/tcg-target.h b/tcg/sparc/tcg-target.h
> index a0ed2a3342..dc0a227890 100644
> --- a/tcg/sparc/tcg-target.h
> +++ b/tcg/sparc/tcg-target.h
> @@ -29,6 +29,7 @@
>
>  #define TCG_TARGET_INSN_UNIT_SIZE 4
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 32
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>  #define TCG_TARGET_NB_REGS 32
>
>  typedef enum {
> diff --git a/tcg/tci/tcg-target.h b/tcg/tci/tcg-target.h
> index 086f34e69a..816dc4697c 100644
> --- a/tcg/tci/tcg-target.h
> +++ b/tcg/tci/tcg-target.h
> @@ -43,6 +43,7 @@
>  #define TCG_TARGET_INTERPRETER 1
>  #define TCG_TARGET_INSN_UNIT_SIZE 1
>  #define TCG_TARGET_TLB_DISPLACEMENT_BITS 32
> +#define TCG_TARGET_IMPLEMENTS_DYN_TLB 0
>
>  #if UINTPTR_MAX == UINT32_MAX
>  # define TCG_TARGET_REG_BITS 32
> diff --git a/accel/tcg/cputlb.c b/accel/tcg/cputlb.c
> index 10f1150c62..a3a1614f0e 100644
> --- a/accel/tcg/cputlb.c
> +++ b/accel/tcg/cputlb.c
> @@ -74,6 +74,187 @@ QEMU_BUILD_BUG_ON(sizeof(target_ulong) > sizeof(run_on_cpu_data));
>  QEMU_BUILD_BUG_ON(NB_MMU_MODES > 16);
>  #define ALL_MMUIDX_BITS ((1 << NB_MMU_MODES) - 1)
>
> +#if TCG_TARGET_IMPLEMENTS_DYN_TLB
> +static inline size_t sizeof_tlb(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +    return env->tlb_mask[mmu_idx] + (1 << CPU_TLB_ENTRY_BITS);
> +}
> +
> +static void tlb_window_reset(CPUTLBWindow *window, int64_t ns,
> +                             size_t max_entries)
> +{
> +    window->begin_ns = ns;
> +    window->max_entries = max_entries;
> +}
> +
> +static void tlb_dyn_init(CPUArchState *env)
> +{
> +    int i;
> +
> +    for (i = 0; i < NB_MMU_MODES; i++) {
> +        CPUTLBDesc *desc = &env->tlb_d[i];
> +        size_t n_entries = 1 << CPU_TLB_DYN_DEFAULT_BITS;
> +
> +        tlb_window_reset(&desc->window, get_clock_realtime(), 0);
> +        desc->n_used_entries = 0;
> +        env->tlb_mask[i] = (n_entries - 1) << CPU_TLB_ENTRY_BITS;
> +        env->tlb_table[i] = g_new(CPUTLBEntry, n_entries);
> +        env->iotlb[i] = g_new(CPUIOTLBEntry, n_entries);
> +    }
> +}
> +
> +/**
> + * tlb_mmu_resize_locked() - perform TLB resize bookkeeping; resize if necessary
> + * @env: CPU that owns the TLB
> + * @mmu_idx: MMU index of the TLB
> + *
> + * Called with tlb_lock_held.
> + *
> + * We have two main constraints when resizing a TLB: (1) we only resize it
> + * on a TLB flush (otherwise we'd have to take a perf hit by either rehashing
> + * the array or unnecessarily flushing it), which means we do not control how
> + * frequently the resizing can occur; (2) we don't have access to the guest's
> + * future scheduling decisions, and therefore have to decide the magnitude of
> + * the resize based on past observations.
> + *
> + * In general, a memory-hungry process can benefit greatly from an appropriately
> + * sized TLB, since a guest TLB miss is very expensive. This doesn't mean that
> + * we just have to make the TLB as large as possible; while an oversized TLB
> + * results in minimal TLB miss rates, it also takes longer to be flushed
> + * (flushes can be _very_ frequent), and the reduced locality can also hurt
> + * performance.
> + *
> + * To achieve near-optimal performance for all kinds of workloads, we:
> + *
> + * 1. Aggressively increase the size of the TLB when the use rate of the
> + * TLB being flushed is high, since it is likely that in the near future this
> + * memory-hungry process will execute again, and its memory hungriness will
> + * probably be similar.
> + *
> + * 2. Slowly reduce the size of the TLB as the use rate declines over a
> + * reasonably large time window. The rationale is that if in such a time window
> + * we have not observed a high TLB use rate, it is likely that we won't observe
> + * it in the near future. In that case, once a time window expires we downsize
> + * the TLB to match the maximum use rate observed in the window.
> + *
> + * 3. Try to keep the maximum use rate in a time window in the 30-70% range,
> + * since in that range performance is likely near-optimal. Recall that the TLB
> + * is direct mapped, so we want the use rate to be low (or at least not too
> + * high), since otherwise we are likely to have a significant amount of
> + * conflict misses.
> + */
> +static void tlb_mmu_resize_locked(CPUArchState *env, int mmu_idx)
> +{
> +    CPUTLBDesc *desc = &env->tlb_d[mmu_idx];
> +    size_t old_size = tlb_n_entries(env, mmu_idx);
> +    size_t rate;
> +    size_t new_size = old_size;
> +    int64_t now = get_clock_realtime();
> +    int64_t window_len_ms = 100;
> +    int64_t window_len_ns = window_len_ms * 1000 * 1000;
> +    bool window_expired = now > desc->window.begin_ns + window_len_ns;
> +
> +    if (desc->n_used_entries > desc->window.max_entries) {
> +        desc->window.max_entries = desc->n_used_entries;
> +    }
> +    rate = desc->window.max_entries * 100 / old_size;
> +
> +    if (rate > 70) {
> +        new_size = MIN(old_size << 1, 1 << CPU_TLB_DYN_MAX_BITS);
> +    } else if (rate < 30 && window_expired) {
> +        size_t ceil = pow2ceil(desc->window.max_entries);
> +        size_t expected_rate = desc->window.max_entries * 100 / ceil;
> +
> +        /*
> +         * Avoid undersizing when the max number of entries seen is just below
> +         * a pow2. For instance, if max_entries == 1025, the expected use rate
> +         * would be 1025/2048==50%. However, if max_entries == 1023, we'd get
> +         * 1023/1024==99.9% use rate, so we'd likely end up doubling the size
> +         * later. Thus, make sure that the expected use rate remains below 70%.
> +         * (and since we double the size, that means the lowest rate we'd
> +         * expect to get is 35%, which is still in the 30-70% range where
> +         * we consider that the size is appropriate.)
> +         */
> +        if (expected_rate > 70) {
> +            ceil *= 2;
> +        }
> +        new_size = MAX(ceil, 1 << CPU_TLB_DYN_MIN_BITS);
> +    }
> +
> +    if (new_size == old_size) {
> +        if (window_expired) {
> +            tlb_window_reset(&desc->window, now, desc->n_used_entries);
> +        }
> +        return;
> +    }
> +
> +    g_free(env->tlb_table[mmu_idx]);
> +    g_free(env->iotlb[mmu_idx]);
> +
> +    tlb_window_reset(&desc->window, now, 0);
> +    /* desc->n_used_entries is cleared by the caller */
> +    env->tlb_mask[mmu_idx] = (new_size - 1) << CPU_TLB_ENTRY_BITS;
> +    env->tlb_table[mmu_idx] = g_try_new(CPUTLBEntry, new_size);
> +    env->iotlb[mmu_idx] = g_try_new(CPUIOTLBEntry, new_size);
> +    /*
> +     * If the allocations fail, try smaller sizes. We just freed some
> +     * memory, so going back to half of new_size has a good chance of working.
> +     * Increased memory pressure elsewhere in the system might cause the
> +     * allocations to fail though, so we progressively reduce the allocation
> +     * size, aborting if we cannot even allocate the smallest TLB we support.
> +     */
> +    while (env->tlb_table[mmu_idx] == NULL || env->iotlb[mmu_idx] == NULL) {
> +        if (new_size == (1 << CPU_TLB_DYN_MIN_BITS)) {
> +            error_report("%s: %s", __func__, strerror(errno));
> +            abort();
> +        }
> +        new_size = MAX(new_size >> 1, 1 << CPU_TLB_DYN_MIN_BITS);
> +        env->tlb_mask[mmu_idx] = (new_size - 1) << CPU_TLB_ENTRY_BITS;
> +
> +        g_free(env->tlb_table[mmu_idx]);
> +        g_free(env->iotlb[mmu_idx]);
> +        env->tlb_table[mmu_idx] = g_try_new(CPUTLBEntry, new_size);
> +        env->iotlb[mmu_idx] = g_try_new(CPUIOTLBEntry, new_size);
> +    }
> +}
> +
> +static inline void tlb_table_flush_by_mmuidx(CPUArchState *env, int mmu_idx)
> +{
> +    tlb_mmu_resize_locked(env, mmu_idx);
> +    memset(env->tlb_table[mmu_idx], -1, sizeof_tlb(env, mmu_idx));
> +    env->tlb_d[mmu_idx].n_used_entries = 0;
> +}
> +
> +static inline void tlb_n_used_entries_inc(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +    env->tlb_d[mmu_idx].n_used_entries++;
> +}
> +
> +static inline void tlb_n_used_entries_dec(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +    env->tlb_d[mmu_idx].n_used_entries--;
> +}
> +
> +#else /* !TCG_TARGET_IMPLEMENTS_DYN_TLB */
> +
> +static inline void tlb_dyn_init(CPUArchState *env)
> +{
> +}
> +
> +static inline void tlb_table_flush_by_mmuidx(CPUArchState *env, int mmu_idx)
> +{
> +    memset(env->tlb_table[mmu_idx], -1, sizeof(env->tlb_table[0]));
> +}
> +
> +static inline void tlb_n_used_entries_inc(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +}
> +
> +static inline void tlb_n_used_entries_dec(CPUArchState *env, uintptr_t mmu_idx)
> +{
> +}
> +#endif /* TCG_TARGET_IMPLEMENTS_DYN_TLB */
> +
>  void tlb_init(CPUState *cpu)
>  {
>      CPUArchState *env = cpu->env_ptr;
> @@ -82,6 +263,8 @@ void tlb_init(CPUState *cpu)
>
>      /* Ensure that cpu_reset performs a full flush.  */
>      env->tlb_c.dirty = ALL_MMUIDX_BITS;
> +
> +    tlb_dyn_init(env);
>  }
>
>  /* flush_all_helper: run fn across all cpus
> @@ -122,7 +305,7 @@ void tlb_flush_counts(size_t *pfull, size_t *ppart, size_t *pelide)
>
>  static void tlb_flush_one_mmuidx_locked(CPUArchState *env, int mmu_idx)
>  {
> -    memset(env->tlb_table[mmu_idx], -1, sizeof(env->tlb_table[0]));
> +    tlb_table_flush_by_mmuidx(env, mmu_idx);
>      memset(env->tlb_v_table[mmu_idx], -1, sizeof(env->tlb_v_table[0]));
>      env->tlb_d[mmu_idx].large_page_addr = -1;
>      env->tlb_d[mmu_idx].large_page_mask = -1;
> @@ -234,12 +417,14 @@ static inline bool tlb_entry_is_empty(const CPUTLBEntry *te)
>  }
>
>  /* Called with tlb_c.lock held */
> -static inline void tlb_flush_entry_locked(CPUTLBEntry *tlb_entry,
> +static inline bool tlb_flush_entry_locked(CPUTLBEntry *tlb_entry,
>                                            target_ulong page)
>  {
>      if (tlb_hit_page_anyprot(tlb_entry, page)) {
>          memset(tlb_entry, -1, sizeof(*tlb_entry));
> +        return true;
>      }
> +    return false;
>  }
>
>  /* Called with tlb_c.lock held */
> @@ -250,7 +435,9 @@ static inline void tlb_flush_vtlb_page_locked(CPUArchState *env, int mmu_idx,
>
>      assert_cpu_is_self(ENV_GET_CPU(env));
>      for (k = 0; k < CPU_VTLB_SIZE; k++) {
> -        tlb_flush_entry_locked(&env->tlb_v_table[mmu_idx][k], page);
> +        if (tlb_flush_entry_locked(&env->tlb_v_table[mmu_idx][k], page)) {
> +            tlb_n_used_entries_dec(env, mmu_idx);
> +        }
>      }
>  }
>
> @@ -267,7 +454,9 @@ static void tlb_flush_page_locked(CPUArchState *env, int midx,
>                    midx, lp_addr, lp_mask);
>          tlb_flush_one_mmuidx_locked(env, midx);
>      } else {
> -        tlb_flush_entry_locked(tlb_entry(env, midx, page), page);
> +        if (tlb_flush_entry_locked(tlb_entry(env, midx, page), page)) {
> +            tlb_n_used_entries_dec(env, midx);
> +        }
>          tlb_flush_vtlb_page_locked(env, midx, page);
>      }
>  }
> @@ -444,8 +633,9 @@ void tlb_reset_dirty(CPUState *cpu, ram_addr_t start1, ram_addr_t length)
>      qemu_spin_lock(&env->tlb_c.lock);
>      for (mmu_idx = 0; mmu_idx < NB_MMU_MODES; mmu_idx++) {
>          unsigned int i;
> +        unsigned int n = tlb_n_entries(env, mmu_idx);
>
> -        for (i = 0; i < CPU_TLB_SIZE; i++) {
> +        for (i = 0; i < n; i++) {
>              tlb_reset_dirty_range_locked(&env->tlb_table[mmu_idx][i], start1,
>                                           length);
>          }
> @@ -607,6 +797,7 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
>          /* Evict the old entry into the victim tlb.  */
>          copy_tlb_helper_locked(tv, te);
>          env->iotlb_v[mmu_idx][vidx] = env->iotlb[mmu_idx][index];
> +        tlb_n_used_entries_dec(env, mmu_idx);
>      }
>
>      /* refill the tlb */
> @@ -658,6 +849,7 @@ void tlb_set_page_with_attrs(CPUState *cpu, target_ulong vaddr,
>      }
>
>      copy_tlb_helper_locked(te, &tn);
> +    tlb_n_used_entries_inc(env, mmu_idx);
>      qemu_spin_unlock(&env->tlb_c.lock);
>  }


--
Alex Bennée