Re: [Qemu-devel] [RFC v4 3/9] softmmu: Add helpers for a new slowpath

[alvise rigo]

On Fri, Aug 7, 2015 at 7:03 PM, Alvise Rigo
<address@hidden> wrote:
> 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 SC operation. It sets the linked address and the size of the
> access.
> These helper also update the TLB entry of the page involved in the
> LL/SC for those vCPUs that have the bit set (dirty), 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 <address@hidden>
> Suggested-by: Claudio Fontana <address@hidden>
> Signed-off-by: Alvise Rigo <address@hidden>
> ---
>  cputlb.c                |   3 ++
>  softmmu_llsc_template.h | 124 
> ++++++++++++++++++++++++++++++++++++++++++++++++
>  softmmu_template.h      |  12 +++++
>  3 files changed, 139 insertions(+)
>  create mode 100644 softmmu_llsc_template.h
>
> diff --git a/cputlb.c b/cputlb.c
> index 251eec8..f45afc6 100644
> --- a/cputlb.c
> +++ b/cputlb.c
> @@ -415,6 +415,8 @@ static inline void lookup_and_reset_cpus_ll_addr(hwaddr 
> addr, hwaddr size)
>
>  #define MMUSUFFIX _mmu
>
> +/* Generates LoadLink/StoreConditional helpers in softmmu_template.h */
> +#define GEN_EXCLUSIVE_HELPERS
>  #define SHIFT 0
>  #include "softmmu_template.h"
>
> @@ -427,6 +429,7 @@ static inline void lookup_and_reset_cpus_ll_addr(hwaddr 
> addr, hwaddr size)
>  #define SHIFT 3
>  #include "softmmu_template.h"
>  #undef MMUSUFFIX
> +#undef GEN_EXCLUSIVE_HELPERS
>
>  #define MMUSUFFIX _cmmu
>  #undef GETPC_ADJ
> diff --git a/softmmu_llsc_template.h b/softmmu_llsc_template.h
> new file mode 100644
> index 0000000..d2e92b4
> --- /dev/null
> +++ b/softmmu_llsc_template.h
> @@ -0,0 +1,124 @@
> +/*
> + *  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 <address@hidden>
> + *
> + * 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_legacy glue(glue(helper_be_ld, USUFFIX), MMUSUFFIX)
> +#define helper_st_legacy 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_legacy glue(glue(helper_le_ld, USUFFIX), MMUSUFFIX)
> +#define helper_st_legacy glue(glue(helper_le_st, SUFFIX), MMUSUFFIX)

Wouldn't be better here to not use the helpers from softmmu_template.h?
Doing so, in softmmu_template.h we don't need to differentiate the
normal stores from the SCs
This at a cost of some additional boilerplate in softmmu_llsc_template.h.

Thanks,
alvise

> +#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_legacy glue(glue(helper_ret_ld, USUFFIX), MMUSUFFIX)
> +#define helper_st_legacy 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;
> +    hwaddr hw_addr;
> +    unsigned mmu_idx = get_mmuidx(oi);
> +
> +    /* Use the proper load helper from cpu_ldst.h */
> +    ret = helper_ld_legacy(env, addr, mmu_idx, 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;
> +
> +    cpu_physical_memory_clear_excl_dirty(hw_addr, 
> ENV_GET_CPU(env)->cpu_index);
> +    /* If all the vCPUs have the EXCL bit set for this page there is no need
> +     * to request any flush. */
> +    if (cpu_physical_memory_excl_is_dirty(hw_addr, smp_cpus)) {
> +        CPU_FOREACH(cpu) {
> +            if (current_cpu != cpu) {
> +                if (cpu_physical_memory_excl_is_dirty(hw_addr,
> +                                                    cpu->cpu_index)) {
> +                    cpu_physical_memory_clear_excl_dirty(hw_addr,
> +                                                         cpu->cpu_index);
> +                    tlb_flush(cpu, 1);
> +                }
> +            }
> +        }
> +    }
> +
> +    env->excl_protected_range.begin = hw_addr;
> +    env->excl_protected_range.end = 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;
> +
> +    return ret;
> +}
> +
> +WORD_TYPE helper_stcond_name(CPUArchState *env, target_ulong addr,
> +                             DATA_TYPE val, TCGMemOpIdx oi,
> +                             uintptr_t retaddr)
> +{
> +    WORD_TYPE ret;
> +    unsigned mmu_idx = get_mmuidx(oi);
> +
> +    /* 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.*/
> +    env->excl_succeeded = 1;
> +    helper_st_legacy(env, addr, val, mmu_idx, retaddr);
> +
> +    if (env->excl_succeeded) {
> +        env->excl_succeeded = 0;
> +        ret = 0;
> +    } else {
> +        ret = 1;
> +    }
> +
> +    return ret;
> +}
> +
> +#undef helper_ldlink_name
> +#undef helper_stcond_name
> +#undef helper_ld_legacy
> +#undef helper_st_legacy
> diff --git a/softmmu_template.h b/softmmu_template.h
> index e4431e8..ad65d20 100644
> --- a/softmmu_template.h
> +++ b/softmmu_template.h
> @@ -640,6 +640,18 @@ 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
> --
> 2.5.0
>