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

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

Pranith Kumar <bobby.prani@gmail.com> writes:

> Can someone please pick this up?

It needs to be re-posted with the review tag and ping Paolo re: async
work for KVM.

>
> Thanks,
>
> On Fri, Feb 24, 2017 at 12:42 AM, Pranith Kumar <bobby.prani@gmail.com> wrote:
>> 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
>>


--
Alex Bennée