linux-user/aarch64: Signal SEGV_MTEAERR for async tag check error

The real kernel collects _TIF_MTE_ASYNC_FAULT into the current thread's
state on any kernel entry (interrupt, exception etc), and then delivers
the signal in advance of resuming the thread.

This means that while the signal won't be delivered immediately, it will
not be delayed forever -- at minimum it will be delivered after the next
clock interrupt.

We don't have a clock interrupt in linux-user, so we issue a cpu_kick
to signal a return to the main loop at the end of the current TB.

Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20210212184902.1251044-29-richard.henderson@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

linux-user/aarch64/cpu_loop.c

@@ -164,6 +164,17 @@ void cpu_loop(CPUARMState *env)
             EXCP_DUMP(env, "qemu: unhandled CPU exception 0x%x - aborting\n", trapnr);
             abort();
         }
+
+        /* Check for MTE asynchronous faults */
+        if (unlikely(env->cp15.tfsr_el[0])) {
+            env->cp15.tfsr_el[0] = 0;
+            info.si_signo = TARGET_SIGSEGV;
+            info.si_errno = 0;
+            info._sifields._sigfault._addr = 0;
+            info.si_code = TARGET_SEGV_MTEAERR;
+            queue_signal(env, info.si_signo, QEMU_SI_FAULT, &info);
+        }
+
         process_pending_signals(env);
         /* Exception return on AArch64 always clears the exclusive monitor,
          * so any return to running guest code implies this.

linux-user/aarch64/target_signal.h

@@ -21,6 +21,7 @@ typedef struct target_sigaltstack {
 
 #include "../generic/signal.h"
 
+#define TARGET_SEGV_MTEAERR  8  /* Asynchronous ARM MTE error */
 #define TARGET_SEGV_MTESERR  9  /* Synchronous ARM MTE exception */
 
 #define TARGET_ARCH_HAS_SETUP_FRAME

target/arm/mte_helper.c

@@ -565,6 +565,16 @@ static void mte_check_fail(CPUARMState *env, uint32_t desc,
             select = 0;
         }
         env->cp15.tfsr_el[el] |= 1 << select;
+#ifdef CONFIG_USER_ONLY
+        /*
+         * Stand in for a timer irq, setting _TIF_MTE_ASYNC_FAULT,
+         * which then sends a SIGSEGV when the thread is next scheduled.
+         * This cpu will return to the main loop at the end of the TB,
+         * which is rather sooner than "normal".  But the alternative
+         * is waiting until the next syscall.
+         */
+        qemu_cpu_kick(env_cpu(env));
+#endif
         break;
 
     default: