Re: [Qemu-devel] [PATCH v1 3/3] tcg-runtime: short-circuit lookup_tb_ptr on IRQs

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

Paolo Bonzini <pbonzini@redhat.com> writes:

> On 14/06/2017 17:45, Richard Henderson wrote:
>> While the next TB would detect the exit flag has been set there is no
>> point if we can exit sooner. We also check cpu->interrupt_request as
>> some front-ends can set it rather than using the cpu_interrupt() API
>> call and would normally be expecting the IRQ to get picked up on the
>> previously fairly regular exits from the run loop.
>
> This is not what happens actually; it's not about front-ends setting
> cpu->interrupt_request, it's about front-ends doing exit_tb when they
> wanted to re-evaluate cpu_handle_interrupt.
>
> cpu_exit is used when device code causes a rising edge in
> cpu->interrupt_request.  What we have here is that the MSR write causes
> cc->cpu_exec_interrupt's return value to change from false to true.
>
> I think this is a band-aid, and would rather fix the front-ends as in
> Emilio's patch.

It seems a shame to cause all msr accesses to trigger and exit when we
only care about the unmasking case. How about:


Author: Alex Bennée <alex.bennee@linaro.org>
Date:   Wed Jun 14 18:46:01 2017 +0100

    target/arm/op_helper: ensure we exit the run-loop

    When IRQs are un-masked we need to ensure the run-loop is exited so we
    can evaluate arm_cpu_do_interrupt.

    Signed-off-by: Alex Bennée <alex.bennee@linaro.org>

diff --git a/target/arm/op_helper.c b/target/arm/op_helper.c
index 2a85666579..7e67bb3db2 100644
--- a/target/arm/op_helper.c
+++ b/target/arm/op_helper.c
@@ -835,6 +835,9 @@ void HELPER(msr_i_pstate)(CPUARMState *env, uint32_t op, uint32_t imm)
         break;
     case 0x1f: /* DAIFClear */
         env->daif &= ~((imm << 6) & PSTATE_DAIF);
+        /* This may result in pending IRQs being unmasked so ensure we
+           exit the loop */
+        cpu_exit(ENV_GET_CPU(env));
         break;
     default:
         g_assert_not_reached();