Re: [Qemu-devel] [RFC v7 10/16] softmmu: Protect MMIO exclusive range

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

Alvise Rigo <a.rigo@virtualopensystems.com> writes:

> As for the RAM case, also the MMIO exclusive ranges have to be protected
> by other CPU's accesses. In order to do that, we flag the accessed
> MemoryRegion to mark that an exclusive access has been performed and is
> not concluded yet.
>
> This flag will force the other CPUs to invalidate the exclusive range in
> case of collision.
>
> Suggested-by: Jani Kokkonen <jani.kokkonen@huawei.com>
> Suggested-by: Claudio Fontana <claudio.fontana@huawei.com>
> Signed-off-by: Alvise Rigo <a.rigo@virtualopensystems.com>
> ---
>  cputlb.c                | 20 +++++++++++++-------
>  include/exec/memory.h   |  1 +
>  softmmu_llsc_template.h | 11 +++++++----
>  softmmu_template.h      | 22 ++++++++++++++++++++++
>  4 files changed, 43 insertions(+), 11 deletions(-)
>
> diff --git a/cputlb.c b/cputlb.c
> index 87d09c8..06ce2da 100644
> --- a/cputlb.c
> +++ b/cputlb.c
> @@ -496,19 +496,25 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, target_ulong addr)
>  /* For every vCPU compare the exclusive address and reset it in case of a
>   * match. Since only one vCPU is running at once, no lock has to be held to
>   * guard this operation. */
> -static inline void lookup_and_reset_cpus_ll_addr(hwaddr addr, hwaddr size)
> +static inline bool lookup_and_reset_cpus_ll_addr(hwaddr addr, hwaddr size)
>  {
>      CPUState *cpu;
> +    bool ret = false;
>
>      CPU_FOREACH(cpu) {
> -        if (cpu->excl_protected_range.begin != EXCLUSIVE_RESET_ADDR &&
> -            ranges_overlap(cpu->excl_protected_range.begin,
> -                           cpu->excl_protected_range.end -
> -                           cpu->excl_protected_range.begin,
> -                           addr, size)) {
> -            cpu->excl_protected_range.begin = EXCLUSIVE_RESET_ADDR;
> +        if (current_cpu != cpu) {

I'm confused by this change. I don't see anywhere in the MMIO handling
why we would want to change skipping the CPU. Perhaps this belongs in
the previous patch? Maybe the function should really be
lookup_and_maybe_reset_other_cpu_ll_addr?

> +            if (cpu->excl_protected_range.begin != EXCLUSIVE_RESET_ADDR &&
> +                ranges_overlap(cpu->excl_protected_range.begin,
> +                               cpu->excl_protected_range.end -
> +                               cpu->excl_protected_range.begin,
> +                               addr, size)) {
> +                cpu->excl_protected_range.begin = EXCLUSIVE_RESET_ADDR;
> +                ret = true;
> +            }
>          }
>      }
> +
> +    return ret;
>  }
>
>  #define MMUSUFFIX _mmu
> diff --git a/include/exec/memory.h b/include/exec/memory.h
> index 71e0480..bacb3ad 100644
> --- a/include/exec/memory.h
> +++ b/include/exec/memory.h
> @@ -171,6 +171,7 @@ struct MemoryRegion {
>      bool rom_device;
>      bool flush_coalesced_mmio;
>      bool global_locking;
> +    bool pending_excl_access; /* A vCPU issued an exclusive access */
>      uint8_t dirty_log_mask;
>      ram_addr_t ram_addr;
>      Object *owner;
> diff --git a/softmmu_llsc_template.h b/softmmu_llsc_template.h
> index 101f5e8..b4712ba 100644
> --- a/softmmu_llsc_template.h
> +++ b/softmmu_llsc_template.h
> @@ -81,15 +81,18 @@ WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong addr,
>                  }
>              }
>          }
> +        /* For this vCPU, just update the TLB entry, no need to flush. */
> +        env->tlb_table[mmu_idx][index].addr_write |= TLB_EXCL;
>      } else {
> -        hw_error("EXCL accesses to MMIO regions not supported yet.");
> +        /* Set a pending exclusive access in the MemoryRegion */
> +        MemoryRegion *mr = iotlb_to_region(this,
> +                                           env->iotlb[mmu_idx][index].addr,
> +                                           env->iotlb[mmu_idx][index].attrs);
> +        mr->pending_excl_access = true;
>      }
>
>      cc->cpu_set_excl_protected_range(this, hw_addr, DATA_SIZE);
>
> -    /* For this vCPU, just update the TLB entry, no need to flush. */
> -    env->tlb_table[mmu_idx][index].addr_write |= TLB_EXCL;
> -
>      /* From now on we are in LL/SC context */
>      this->ll_sc_context = true;
>
> diff --git a/softmmu_template.h b/softmmu_template.h
> index c54bdc9..71c5152 100644
> --- a/softmmu_template.h
> +++ b/softmmu_template.h
> @@ -360,6 +360,14 @@ static inline void glue(io_write, SUFFIX)(CPUArchState *env,
>      MemoryRegion *mr = iotlb_to_region(cpu, physaddr, iotlbentry->attrs);
>
>      physaddr = (physaddr & TARGET_PAGE_MASK) + addr;
> +
> +    /* Invalidate the exclusive range that overlaps this access */
> +    if (mr->pending_excl_access) {
> +        if (lookup_and_reset_cpus_ll_addr(physaddr, 1 << SHIFT)) {
> +            mr->pending_excl_access = false;
> +        }
> +    }
> +
>      if (mr != &io_mem_rom && mr != &io_mem_notdirty && !cpu->can_do_io) {
>          cpu_io_recompile(cpu, retaddr);
>      }
> @@ -504,6 +512,13 @@ void helper_le_st_name(CPUArchState *env, target_ulong addr, DATA_TYPE val,
>                  glue(helper_le_st_name, _do_mmio_access)(env, val, addr, oi,
>                                                           mmu_idx, index,
>                                                           retaddr);
> +                /* N.B.: Here excl_succeeded == true means that this access
> +                 * comes from an exclusive instruction. */
> +                if (cpu->excl_succeeded) {
> +                    MemoryRegion *mr = iotlb_to_region(cpu, iotlbentry->addr,
> +                                                       iotlbentry->attrs);
> +                    mr->pending_excl_access = false;
> +                }
>              } else {
>                  glue(helper_le_st_name, _do_ram_access)(env, val, addr, oi,
>                                                          mmu_idx, index,
> @@ -655,6 +670,13 @@ void helper_be_st_name(CPUArchState *env, target_ulong addr, DATA_TYPE val,
>                  glue(helper_be_st_name, _do_mmio_access)(env, val, addr, oi,
>                                                           mmu_idx, index,
>                                                           retaddr);
> +                /* N.B.: Here excl_succeeded == true means that this access
> +                 * comes from an exclusive instruction. */
> +                if (cpu->excl_succeeded) {
> +                    MemoryRegion *mr = iotlb_to_region(cpu, iotlbentry->addr,
> +                                                       iotlbentry->attrs);
> +                    mr->pending_excl_access = false;
> +                }

My comments about duplication on previous patches still stand.

>              } else {
>                  glue(helper_be_st_name, _do_ram_access)(env, val, addr, oi,
>                                                          mmu_idx, index,


--
Alex Bennée