Re: [Qemu-devel] [RFC v7 07/16] softmmu: Add helpers for a new slowpath

[alvise rigo <a.rigo@virtualopensystems.com>]

On Thu, Feb 11, 2016 at 5:33 PM, Alex Bennée <alex.bennee@linaro.org> wrote:
>
> Alvise Rigo <a.rigo@virtualopensystems.com> writes:
>
>> The new helpers rely on the legacy ones to perform the actual read/write.
>>
>> The LoadLink helper (helper_ldlink_name) prepares the way for the
>> following StoreCond operation. It sets the linked address and the size
>> of the access. The LoadLink helper also updates the TLB entry of the
>> page involved in the LL/SC to all vCPUs by forcing a TLB flush, so that
>> the following accesses made by all the vCPUs will follow the slow path.
>>
>> The StoreConditional helper (helper_stcond_name) returns 1 if the
>> store has to fail due to a concurrent access to the same page by
>> another vCPU. A 'concurrent access' can be a store made by *any* vCPU
>> (although, some implementations allow stores made by the CPU that issued
>> the LoadLink).
>>
>> 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                |   3 ++
>>  include/qom/cpu.h       |   5 ++
>>  softmmu_llsc_template.h | 133 ++++++++++++++++++++++++++++++++++++++++++++++++
>>  softmmu_template.h      |  12 +++++
>>  tcg/tcg.h               |  31 +++++++++++
>>  5 files changed, 184 insertions(+)
>>  create mode 100644 softmmu_llsc_template.h
>>
>> diff --git a/cputlb.c b/cputlb.c
>> index f6fb161..ce6d720 100644
>> --- a/cputlb.c
>> +++ b/cputlb.c
>> @@ -476,6 +476,8 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, target_ulong addr)
>>
>>  #define MMUSUFFIX _mmu
>>
>> +/* Generates LoadLink/StoreConditional helpers in softmmu_template.h */
>> +#define GEN_EXCLUSIVE_HELPERS
>>  #define SHIFT 0
>>  #include "softmmu_template.h"
>>
>> @@ -488,6 +490,7 @@ tb_page_addr_t get_page_addr_code(CPUArchState *env1, target_ulong addr)
>>  #define SHIFT 3
>>  #include "softmmu_template.h"
>>  #undef MMUSUFFIX
>> +#undef GEN_EXCLUSIVE_HELPERS
>>
>>  #define MMUSUFFIX _cmmu
>>  #undef GETPC_ADJ
>> diff --git a/include/qom/cpu.h b/include/qom/cpu.h
>> index 682c81d..6f6c1c0 100644
>> --- a/include/qom/cpu.h
>> +++ b/include/qom/cpu.h
>> @@ -351,10 +351,15 @@ struct CPUState {
>>       */
>>      bool throttle_thread_scheduled;
>>
>> +    /* Used by the atomic insn translation backend. */
>> +    bool ll_sc_context;
>>      /* vCPU's exclusive addresses range.
>>       * The address is set to EXCLUSIVE_RESET_ADDR if the vCPU is not
>>       * in the middle of a LL/SC. */
>>      struct Range excl_protected_range;
>> +    /* Used to carry the SC result but also to flag a normal store access made
>> +     * by a stcond (see softmmu_template.h). */
>> +    bool excl_succeeded;
>>
>>      /* Note that this is accessed at the start of every TB via a negative
>>         offset from AREG0.  Leave this field at the end so as to make the
>> diff --git a/softmmu_llsc_template.h b/softmmu_llsc_template.h
>> new file mode 100644
>> index 0000000..101f5e8
>> --- /dev/null
>> +++ b/softmmu_llsc_template.h
>> @@ -0,0 +1,133 @@
>> +/*
>> + *  Software MMU support (esclusive load/store operations)
>> + *
>> + * Generate helpers used by TCG for qemu_ldlink/stcond ops.
>> + *
>> + * Included from softmmu_template.h only.
>> + *
>> + * Copyright (c) 2015 Virtual Open Systems
>> + *
>> + * Authors:
>> + *  Alvise Rigo <a.rigo@virtualopensystems.com>
>> + *
>> + * This library is free software; you can redistribute it and/or
>> + * modify it under the terms of the GNU Lesser General Public
>> + * License as published by the Free Software Foundation; either
>> + * version 2 of the License, or (at your option) any later version.
>> + *
>> + * This library is distributed in the hope that it will be useful,
>> + * but WITHOUT ANY WARRANTY; without even the implied warranty of
>> + * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
>> + * Lesser General Public License for more details.
>> + *
>> + * You should have received a copy of the GNU Lesser General Public
>> + * License along with this library; if not, see <http://www.gnu.org/licenses/>.
>> + */
>> +
>> +/* This template does not generate together the le and be version, but only one
>> + * of the two depending on whether BIGENDIAN_EXCLUSIVE_HELPERS has been set.
>> + * The same nomenclature as softmmu_template.h is used for the exclusive
>> + * helpers.  */
>> +
>> +#ifdef BIGENDIAN_EXCLUSIVE_HELPERS
>> +
>> +#define helper_ldlink_name  glue(glue(helper_be_ldlink, USUFFIX), MMUSUFFIX)
>> +#define helper_stcond_name  glue(glue(helper_be_stcond, SUFFIX), MMUSUFFIX)
>> +#define helper_ld glue(glue(helper_be_ld, USUFFIX), MMUSUFFIX)
>> +#define helper_st glue(glue(helper_be_st, SUFFIX), MMUSUFFIX)
>> +
>> +#else /* LE helpers + 8bit helpers (generated only once for both LE end BE) */
>> +
>> +#if DATA_SIZE > 1
>> +#define helper_ldlink_name  glue(glue(helper_le_ldlink, USUFFIX), MMUSUFFIX)
>> +#define helper_stcond_name  glue(glue(helper_le_stcond, SUFFIX), MMUSUFFIX)
>> +#define helper_ld glue(glue(helper_le_ld, USUFFIX), MMUSUFFIX)
>> +#define helper_st glue(glue(helper_le_st, SUFFIX), MMUSUFFIX)
>> +#else /* DATA_SIZE <= 1 */
>> +#define helper_ldlink_name  glue(glue(helper_ret_ldlink, USUFFIX), MMUSUFFIX)
>> +#define helper_stcond_name  glue(glue(helper_ret_stcond, SUFFIX), MMUSUFFIX)
>> +#define helper_ld glue(glue(helper_ret_ld, USUFFIX), MMUSUFFIX)
>> +#define helper_st glue(glue(helper_ret_st, SUFFIX), MMUSUFFIX)
>> +#endif
>> +
>> +#endif
>> +
>> +WORD_TYPE helper_ldlink_name(CPUArchState *env, target_ulong addr,
>> +                                TCGMemOpIdx oi, uintptr_t retaddr)
>> +{
>> +    WORD_TYPE ret;
>> +    int index;
>> +    CPUState *cpu, *this = ENV_GET_CPU(env);
>
> I'd rename this to this_cpu and move the *cpu definition to inside the
> if {} where it is used so no confusion occurs.
>
>> +    CPUClass *cc = CPU_GET_CLASS(this);
>> +    hwaddr hw_addr;
>> +    unsigned mmu_idx = get_mmuidx(oi);
>> +
>> +    /* Use the proper load helper from cpu_ldst.h */
>> +    ret = helper_ld(env, addr, oi, retaddr);
>> +
>> +    index = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
>> +
>> +    /* hw_addr = hwaddr of the page (i.e. section->mr->ram_addr + xlat)
>> +     * plus the offset (i.e. addr & ~TARGET_PAGE_MASK) */
>> +    hw_addr = (env->iotlb[mmu_idx][index].addr & TARGET_PAGE_MASK) + addr;
>> +    if (likely(!(env->tlb_table[mmu_idx][index].addr_read & TLB_MMIO))) {
>> +        /* If all the vCPUs have the EXCL bit set for this page there is no need
>> +         * to request any flush. */
>> +        if (!cpu_physical_memory_is_excl(hw_addr)) {
>> +            cpu_physical_memory_set_excl(hw_addr);
>> +            CPU_FOREACH(cpu) {
>> +                if (current_cpu != cpu) {
>
> Why use current_cpu is we have this_cpu? I'd argue the check should use
> what we've been passed over global (and future TLS value).

Indeed, it makes more sense to do as you suggested.

Thank you,
alvise

>
>> +                    tlb_flush(cpu, 1);
>> +                }
>> +            }
>> +        }
>> +    } else {
>> +        hw_error("EXCL accesses to MMIO regions not supported yet.");
>> +    }
>> +
>> +    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;
>> +
>> +    return ret;
>> +}
>> +
>> +WORD_TYPE helper_stcond_name(CPUArchState *env, target_ulong addr,
>> +                             DATA_TYPE val, TCGMemOpIdx oi,
>> +                             uintptr_t retaddr)
>> +{
>> +    WORD_TYPE ret;
>> +    CPUState *cpu = ENV_GET_CPU(env);
>> +
>> +    if (!cpu->ll_sc_context) {
>> +        ret = 1;
>> +    } else {
>> +        /* We set it preventively to true to distinguish the following legacy
>> +         * access as one made by the store conditional wrapper. If the store
>> +         * conditional does not succeed, the value will be set to 0.*/
>> +        cpu->excl_succeeded = true;
>> +        helper_st(env, addr, val, oi, retaddr);
>> +
>> +        if (cpu->excl_succeeded) {
>> +            ret = 0;
>> +        } else {
>> +            ret = 1;
>> +        }
>> +    }
>> +
>> +    /* Unset LL/SC context */
>> +    cpu->ll_sc_context = false;
>> +    cpu->excl_succeeded = false;
>> +    cpu->excl_protected_range.begin = EXCLUSIVE_RESET_ADDR;
>> +
>> +    return ret;
>> +}
>> +
>> +#undef helper_ldlink_name
>> +#undef helper_stcond_name
>> +#undef helper_ld
>> +#undef helper_st
>> diff --git a/softmmu_template.h b/softmmu_template.h
>> index 6279437..4332db2 100644
>> --- a/softmmu_template.h
>> +++ b/softmmu_template.h
>> @@ -622,6 +622,18 @@ void probe_write(CPUArchState *env, target_ulong addr, int mmu_idx,
>>  #endif
>>  #endif /* !defined(SOFTMMU_CODE_ACCESS) */
>>
>> +#ifdef GEN_EXCLUSIVE_HELPERS
>> +
>> +#if DATA_SIZE > 1 /* The 8-bit helpers are generate along with LE helpers */
>> +#define BIGENDIAN_EXCLUSIVE_HELPERS
>> +#include "softmmu_llsc_template.h"
>> +#undef BIGENDIAN_EXCLUSIVE_HELPERS
>> +#endif
>> +
>> +#include "softmmu_llsc_template.h"
>> +
>> +#endif /* !defined(GEN_EXCLUSIVE_HELPERS) */
>> +
>>  #undef READ_ACCESS_TYPE
>>  #undef SHIFT
>>  #undef DATA_TYPE
>> diff --git a/tcg/tcg.h b/tcg/tcg.h
>> index a696922..3e050a4 100644
>> --- a/tcg/tcg.h
>> +++ b/tcg/tcg.h
>> @@ -968,6 +968,21 @@ tcg_target_ulong helper_be_ldul_mmu(CPUArchState *env, target_ulong addr,
>>                                      TCGMemOpIdx oi, uintptr_t retaddr);
>>  uint64_t helper_be_ldq_mmu(CPUArchState *env, target_ulong addr,
>>                             TCGMemOpIdx oi, uintptr_t retaddr);
>> +/* Exclusive variants */
>> +tcg_target_ulong helper_ret_ldlinkub_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_le_ldlinkuw_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_le_ldlinkul_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +uint64_t helper_le_ldlinkq_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_be_ldlinkuw_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_be_ldlinkul_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>> +uint64_t helper_be_ldlinkq_mmu(CPUArchState *env, target_ulong addr,
>> +                                            TCGMemOpIdx oi, uintptr_t retaddr);
>>
>>  /* Value sign-extended to tcg register size.  */
>>  tcg_target_ulong helper_ret_ldsb_mmu(CPUArchState *env, target_ulong addr,
>> @@ -1010,6 +1025,22 @@ uint32_t helper_be_ldl_cmmu(CPUArchState *env, target_ulong addr,
>>                              TCGMemOpIdx oi, uintptr_t retaddr);
>>  uint64_t helper_be_ldq_cmmu(CPUArchState *env, target_ulong addr,
>>                              TCGMemOpIdx oi, uintptr_t retaddr);
>> +/* Exclusive variants */
>> +tcg_target_ulong helper_ret_stcondb_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint8_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_le_stcondw_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint16_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_le_stcondl_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint32_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +uint64_t helper_le_stcondq_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint64_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_be_stcondw_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint16_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +tcg_target_ulong helper_be_stcondl_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint32_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +uint64_t helper_be_stcondq_mmu(CPUArchState *env, target_ulong addr,
>> +                            uint64_t val, TCGMemOpIdx oi, uintptr_t retaddr);
>> +
>>
>>  /* Temporary aliases until backends are converted.  */
>>  #ifdef TARGET_WORDS_BIGENDIAN
>
>
> --
> Alex Bennée