[Qemu-devel] [RFC v3 03/13] softmmu: Add helpers for a new slow-path

[Alvise Rigo <a.rigo@virtualopensystems.com>]

The new helpers rely on the legacy ones to perform the actual read/write.

The StoreConditional helper (helper_le_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).

These helpers also update the TLB entry of the page involved in the
LL/SC, so that all the following accesses made by any vCPU will follow
the slow path.
In real multi-threading, these helpers will require to temporarily pause
the execution of the other vCPUs in order to update accordingly (flush)
the TLB cache.

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 +
 softmmu_llsc_template.h | 155 ++++++++++++++++++++++++++++++++++++++++++++++++
 softmmu_template.h      |   4 ++
 tcg/tcg.h               |  18 ++++++
 4 files changed, 180 insertions(+)
 create mode 100644 softmmu_llsc_template.h

diff --git a/cputlb.c b/cputlb.c
index 0aca407..fa38714 100644
--- a/cputlb.c
+++ b/cputlb.c
@@ -475,6 +475,8 @@ 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"
 
@@ -487,6 +489,7 @@ 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/softmmu_llsc_template.h b/softmmu_llsc_template.h
new file mode 100644
index 0000000..81e9d8e
--- /dev/null
+++ b/softmmu_llsc_template.h
@@ -0,0 +1,155 @@
+/*
+ *  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/>.
+ */
+
+/*
+ * TODO configurations not implemented:
+ *     - Signed/Unsigned Big-endian
+ *     - Signed Little-endian
+ * */
+
+#if DATA_SIZE > 1
+#define helper_le_ldlink_name  glue(glue(helper_le_ldlink, USUFFIX), MMUSUFFIX)
+#define helper_le_stcond_name  glue(glue(helper_le_stcond, SUFFIX), MMUSUFFIX)
+#else
+#define helper_le_ldlink_name  glue(glue(helper_ret_ldlink, USUFFIX), MMUSUFFIX)
+#define helper_le_stcond_name  glue(glue(helper_ret_stcond, SUFFIX), MMUSUFFIX)
+#endif
+
+/* helpers from cpu_ldst.h, byte-order independent versions */
+#if DATA_SIZE > 1
+#define helper_ld_legacy glue(glue(helper_le_ld, USUFFIX), MMUSUFFIX)
+#define helper_st_legacy glue(glue(helper_le_st, SUFFIX), MMUSUFFIX)
+#else
+#define helper_ld_legacy glue(glue(helper_ret_ld, USUFFIX), MMUSUFFIX)
+#define helper_st_legacy glue(glue(helper_ret_st, SUFFIX), MMUSUFFIX)
+#endif
+
+#define is_write_tlb_entry_set(env, page, index)                             \
+({                                                                           \
+    (addr & TARGET_PAGE_MASK)                                                \
+         == ((env->tlb_table[mmu_idx][index].addr_write) &                   \
+                 (TARGET_PAGE_MASK | TLB_INVALID_MASK));                     \
+})                                                                           \
+
+#define EXCLUSIVE_RESET_ADDR ULLONG_MAX
+
+WORD_TYPE helper_le_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);
+
+    /* The last legacy access ensures that the TLB and IOTLB entry for 'addr'
+     * have been created. */
+    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;
+
+    /* Set the exclusive-protected hwaddr. */
+    env->excl_protected_hwaddr = hw_addr;
+    env->ll_sc_context = true;
+
+    /* No need to mask hw_addr with TARGET_PAGE_MASK since
+     * cpu_physical_memory_excl_is_dirty() will take care of that. */
+    if (cpu_physical_memory_excl_is_dirty(hw_addr)) {
+        cpu_physical_memory_clear_excl_dirty(hw_addr);
+
+        /* Invalidate the TLB entry for the other processors. The next TLB
+         * entries for this page will have the TLB_EXCL flag set. */
+        CPU_FOREACH(cpu) {
+            if (cpu != current_cpu) {
+                tlb_flush(cpu, 1);
+            }
+        }
+    }
+
+    /* 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_le_stcond_name(CPUArchState *env, target_ulong addr,
+                                DATA_TYPE val, TCGMemOpIdx oi,
+                                uintptr_t retaddr)
+{
+    WORD_TYPE ret;
+    int index;
+    hwaddr hw_addr;
+    unsigned mmu_idx = get_mmuidx(oi);
+
+    /* If the TLB entry is not the right one, create it. */
+    index = (addr >> TARGET_PAGE_BITS) & (CPU_TLB_SIZE - 1);
+    if (!is_write_tlb_entry_set(env, addr, index)) {
+        tlb_fill(ENV_GET_CPU(env), addr, MMU_DATA_STORE, mmu_idx, retaddr);
+    }
+
+    /* 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 (!env->ll_sc_context) {
+        /* No LoakLink has been set, the StoreCond has to fail. */
+        return 1;
+    }
+
+    env->ll_sc_context = 0;
+
+    if (cpu_physical_memory_excl_is_dirty(hw_addr)) {
+        /* Another vCPU has accessed the memory after the LoadLink. */
+        ret = 1;
+    } else {
+        helper_st_legacy(env, addr, val, mmu_idx, retaddr);
+
+        /* The StoreConditional succeeded */
+        ret = 0;
+    }
+
+    env->tlb_table[mmu_idx][index].addr_write &= ~TLB_EXCL;
+    env->excl_protected_hwaddr = EXCLUSIVE_RESET_ADDR;
+    /* It's likely that the page will be used again for exclusive accesses,
+     * for this reason we don't flush any TLB cache at the price of some
+     * additional slow paths and we don't set the page bit as dirty.
+     * The EXCL TLB entries will not remain there forever since they will be
+     * eventually removed to serve another guest page; when this happens we
+     * remove also the dirty bit (see cputlb.c).
+     * */
+
+    return ret;
+}
+
+#undef helper_le_ldlink_name
+#undef helper_le_stcond_name
+#undef helper_ld_legacy
+#undef helper_st_legacy
diff --git a/softmmu_template.h b/softmmu_template.h
index 0edd451..bc767f6 100644
--- a/softmmu_template.h
+++ b/softmmu_template.h
@@ -630,6 +630,10 @@ void probe_write(CPUArchState *env, target_ulong addr, int mmu_idx,
 #endif
 #endif /* !defined(SOFTMMU_CODE_ACCESS) */
 
+#ifdef GEN_EXCLUSIVE_HELPERS
+#include "softmmu_llsc_template.h"
+#endif
+
 #undef READ_ACCESS_TYPE
 #undef SHIFT
 #undef DATA_TYPE
diff --git a/tcg/tcg.h b/tcg/tcg.h
index 032fe10..8ca85ab 100644
--- a/tcg/tcg.h
+++ b/tcg/tcg.h
@@ -962,6 +962,15 @@ 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,
+                                         int mmu_idx, uintptr_t retaddr);
+tcg_target_ulong helper_le_ldlinkuw_mmu(CPUArchState *env, target_ulong addr,
+                                        int mmu_idx, uintptr_t retaddr);
+tcg_target_ulong helper_le_ldlinkul_mmu(CPUArchState *env, target_ulong addr,
+                                        int mmu_idx, uintptr_t retaddr);
+uint64_t helper_le_ldlinkq_mmu(CPUArchState *env, target_ulong addr,
+                               int mmu_idx, uintptr_t retaddr);
 
 /* Value sign-extended to tcg register size.  */
 tcg_target_ulong helper_ret_ldsb_mmu(CPUArchState *env, target_ulong addr,
@@ -989,6 +998,15 @@ void helper_be_stl_mmu(CPUArchState *env, target_ulong addr, uint32_t val,
                        TCGMemOpIdx oi, uintptr_t retaddr);
 void helper_be_stq_mmu(CPUArchState *env, target_ulong addr, uint64_t val,
                        TCGMemOpIdx oi, uintptr_t retaddr);
+/* Exclusive variants */
+tcg_target_ulong helper_ret_stcondb_mmu(CPUArchState *env, target_ulong addr,
+                                uint8_t val, int mmu_idx, uintptr_t retaddr);
+tcg_target_ulong helper_le_stcondw_mmu(CPUArchState *env, target_ulong addr,
+                                uint16_t val, int mmu_idx, uintptr_t retaddr);
+tcg_target_ulong helper_le_stcondl_mmu(CPUArchState *env, target_ulong addr,
+                                uint32_t val, int mmu_idx, uintptr_t retaddr);
+uint64_t helper_le_stcondq_mmu(CPUArchState *env, target_ulong addr,
+                                uint64_t val, int mmu_idx, uintptr_t retaddr);
 
 /* Temporary aliases until backends are converted.  */
 #ifdef TARGET_WORDS_BIGENDIAN
-- 
2.4.5