[Qemu-devel] [PATCH v2] mttcg/i386: Patch instruction using async_safe_* framework

[Pranith Kumar <bobby.prani@gmail.com>]

In mttcg, calling pause_all_vcpus() during execution from the
generated TBs causes a deadlock if some vCPU is waiting for exclusive
execution in start_exclusive(). Fix this by using the aync_safe_*
framework instead of pausing vcpus for patching instructions.

CC: Richard Henderson <rth@twiddle.net>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Pranith Kumar <bobby.prani@gmail.com>
---
 hw/i386/kvmvapic.c | 82 ++++++++++++++++++++++++++++++++++--------------------
 1 file changed, 52 insertions(+), 30 deletions(-)

diff --git a/hw/i386/kvmvapic.c b/hw/i386/kvmvapic.c
index 82a4955..11b0d49 100644
--- a/hw/i386/kvmvapic.c
+++ b/hw/i386/kvmvapic.c
@@ -383,8 +383,7 @@ static void patch_byte(X86CPU *cpu, target_ulong addr, uint8_t byte)
     cpu_memory_rw_debug(CPU(cpu), addr, &byte, 1, 1);
 }
 
-static void patch_call(VAPICROMState *s, X86CPU *cpu, target_ulong ip,
-                       uint32_t target)
+static void patch_call(X86CPU *cpu, target_ulong ip, uint32_t target)
 {
     uint32_t offset;
 
@@ -393,23 +392,24 @@ static void patch_call(VAPICROMState *s, X86CPU *cpu, target_ulong ip,
     cpu_memory_rw_debug(CPU(cpu), ip + 1, (void *)&offset, sizeof(offset), 1);
 }
 
-static void patch_instruction(VAPICROMState *s, X86CPU *cpu, target_ulong ip)
+struct PatchInfo {
+    VAPICHandlers *handler;
+    target_ulong ip;
+};
+
+static void do_patch_instruction(CPUState *cs, run_on_cpu_data data)
 {
-    CPUState *cs = CPU(cpu);
-    CPUX86State *env = &cpu->env;
-    VAPICHandlers *handlers;
+    X86CPU *x86_cpu = X86_CPU(cs);
+    CPUX86State *env = &x86_cpu->env;
+    struct PatchInfo *info = (struct PatchInfo *) data.host_ptr;
+    VAPICHandlers *handlers = info->handler;
+    target_ulong ip = info->ip;
     uint8_t opcode[2];
     uint32_t imm32 = 0;
     target_ulong current_pc = 0;
     target_ulong current_cs_base = 0;
     uint32_t current_flags = 0;
 
-    if (smp_cpus == 1) {
-        handlers = &s->rom_state.up;
-    } else {
-        handlers = &s->rom_state.mp;
-    }
-
     if (!kvm_enabled()) {
         cpu_get_tb_cpu_state(env, &current_pc, &current_cs_base,
                              &current_flags);
@@ -421,48 +421,70 @@ static void patch_instruction(VAPICROMState *s, X86CPU *cpu, target_ulong ip)
         }
     }
 
-    pause_all_vcpus();
-
     cpu_memory_rw_debug(cs, ip, opcode, sizeof(opcode), 0);
 
     switch (opcode[0]) {
     case 0x89: /* mov r32 to r/m32 */
-        patch_byte(cpu, ip, 0x50 + modrm_reg(opcode[1]));  /* push reg */
-        patch_call(s, cpu, ip + 1, handlers->set_tpr);
+        patch_byte(x86_cpu, ip, 0x50 + modrm_reg(opcode[1]));  /* push reg */
+        patch_call(x86_cpu, ip + 1, handlers->set_tpr);
         break;
     case 0x8b: /* mov r/m32 to r32 */
-        patch_byte(cpu, ip, 0x90);
-        patch_call(s, cpu, ip + 1, handlers->get_tpr[modrm_reg(opcode[1])]);
+        patch_byte(x86_cpu, ip, 0x90);
+        patch_call(x86_cpu, ip + 1, handlers->get_tpr[modrm_reg(opcode[1])]);
         break;
     case 0xa1: /* mov abs to eax */
-        patch_call(s, cpu, ip, handlers->get_tpr[0]);
+        patch_call(x86_cpu, ip, handlers->get_tpr[0]);
         break;
     case 0xa3: /* mov eax to abs */
-        patch_call(s, cpu, ip, handlers->set_tpr_eax);
+        patch_call(x86_cpu, ip, handlers->set_tpr_eax);
         break;
     case 0xc7: /* mov imm32, r/m32 (c7/0) */
-        patch_byte(cpu, ip, 0x68);  /* push imm32 */
+        patch_byte(x86_cpu, ip, 0x68);  /* push imm32 */
         cpu_memory_rw_debug(cs, ip + 6, (void *)&imm32, sizeof(imm32), 0);
         cpu_memory_rw_debug(cs, ip + 1, (void *)&imm32, sizeof(imm32), 1);
-        patch_call(s, cpu, ip + 5, handlers->set_tpr);
+        patch_call(x86_cpu, ip + 5, handlers->set_tpr);
         break;
     case 0xff: /* push r/m32 */
-        patch_byte(cpu, ip, 0x50); /* push eax */
-        patch_call(s, cpu, ip + 1, handlers->get_tpr_stack);
+        patch_byte(x86_cpu, ip, 0x50); /* push eax */
+        patch_call(x86_cpu, ip + 1, handlers->get_tpr_stack);
         break;
     default:
         abort();
     }
 
-    resume_all_vcpus();
+    g_free(info);
+}
+
+static void patch_instruction(VAPICROMState *s, X86CPU *cpu, target_ulong ip)
+{
+    CPUState *cs = CPU(cpu);
+    VAPICHandlers *handlers;
+    struct PatchInfo *info;
+
+    if (smp_cpus == 1) {
+        handlers = &s->rom_state.up;
+    } else {
+        handlers = &s->rom_state.mp;
+    }
+
+    info  = g_new(struct PatchInfo, 1);
+    info->handler = handlers;
+    info->ip = ip;
 
     if (!kvm_enabled()) {
-        /* Both tb_lock and iothread_mutex will be reset when
-         *  longjmps back into the cpu_exec loop. */
-        tb_lock();
-        tb_gen_code(cs, current_pc, current_cs_base, current_flags, 1);
-        cpu_loop_exit_noexc(cs);
+        const run_on_cpu_func fn = do_patch_instruction;
+
+        async_safe_run_on_cpu(cs, fn, RUN_ON_CPU_HOST_PTR(info));
+        cs->exception_index = EXCP_INTERRUPT;
+        cpu_loop_exit(cs);
     }
+
+    pause_all_vcpus();
+
+    do_patch_instruction(cs, RUN_ON_CPU_HOST_PTR(info));
+
+    resume_all_vcpus();
+    g_free(info);
 }
 
 void vapic_report_tpr_access(DeviceState *dev, CPUState *cs, target_ulong ip,
-- 
2.7.4