[Qemu-devel] [RFC PATCH] target/arm: ensure eret exits the run-loop

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

Previously DISAS_JUMP did ensure this but with the optimisation of
8a6b28c7 (optimize indirect branches) we might not leave the loop.
This means if any pending interrupts are cleared by changing IRQ flags
we might never get around to servicing them. You usually notice this
by seeing the lookup_tb_ptr() helper gainfully chaining TBs together
while cpu->interrupt_request remains high and the exit_request has not
been set.

This breaks amongst other things the OPTEE test suite which executes
an eret from the secure world after a non-secure world IRQ has gone
pending which then never gets serviced.

An alternate approach might be for the exception helpers to ensure the
exit request flag is set if an IRQ is now unmasked.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
CC: Etienne Carriere <etienne.carriere@linaro.org>
CC: Joakim Bech <joakim.bech@linaro.org>
CC: Peter Maydell <peter.maydell@linaro.org>
CC: Emilio G. Cota <cota@braap.org>
CC: Richard Henderson <rth@twiddle.net>
---
 target/arm/translate-a64.c | 3 ++-
 target/arm/translate.c     | 6 ++++--
 2 files changed, 6 insertions(+), 3 deletions(-)

diff --git a/target/arm/translate-a64.c b/target/arm/translate-a64.c
index e55547d95d..3ee88b2590 100644
--- a/target/arm/translate-a64.c
+++ b/target/arm/translate-a64.c
@@ -1788,7 +1788,8 @@ static void disas_uncond_b_reg(DisasContext *s, uint32_t insn)
             return;
         }
         gen_helper_exception_return(cpu_env);
-        s->is_jmp = DISAS_JUMP;
+        /* Must exit loop to check un-masked IRQs */
+        s->is_jmp = DISAS_EXIT;
         return;
     case 5: /* DRPS */
         if (rn != 0x1f) {
diff --git a/target/arm/translate.c b/target/arm/translate.c
index 0862f9e4aa..920fb41395 100644
--- a/target/arm/translate.c
+++ b/target/arm/translate.c
@@ -4475,7 +4475,8 @@ static void gen_rfe(DisasContext *s, TCGv_i32 pc, TCGv_i32 cpsr)
      */
     gen_helper_cpsr_write_eret(cpu_env, cpsr);
     tcg_temp_free_i32(cpsr);
-    s->is_jmp = DISAS_JUMP;
+    /* Must exit loop to check un-masked IRQs */
+    s->is_jmp = DISAS_EXIT;
 }
 
 /* Generate an old-style exception return. Marks pc as dead. */
@@ -9519,7 +9520,8 @@ static void disas_arm_insn(DisasContext *s, unsigned int insn)
                     tmp = load_cpu_field(spsr);
                     gen_helper_cpsr_write_eret(cpu_env, tmp);
                     tcg_temp_free_i32(tmp);
-                    s->is_jmp = DISAS_JUMP;
+                    /* Must exit loop to check un-masked IRQs */
+                    s->is_jmp = DISAS_EXIT;
                 }
             }
             break;
-- 
2.13.0