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Re: [PATCH v2] s390x/tcg: MVCL: Exit to main loop if requested

From: David Hildenbrand
Subject: Re: [PATCH v2] s390x/tcg: MVCL: Exit to main loop if requested
Date: Fri, 4 Oct 2019 14:34:05 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.8.0

On 04.10.19 14:11, Peter Maydell wrote:
> On Fri, 4 Oct 2019 at 09:02, David Hildenbrand <address@hidden> wrote:
>> So shall we leave this patch as-is (adding a summary of what you
>> explained to the description) or shall we somehow factor out the
>> TCG-internal-thingy check?
> Nothing else in target code touches the icount data structures,
> so if this s390 insn needs to make this check I think it ought
> to do it by calling a function implemented by the tcg code;
> that can then have a good name that describes what it's doing
> and a doc comment explaining the reason we need to have it.
> thanks
> -- PMM

I can offer something like this:

diff --git a/include/exec/exec-all.h b/include/exec/exec-all.h
index 49db07ba0b..d370ac0134 100644
--- a/include/exec/exec-all.h
+++ b/include/exec/exec-all.h
@@ -72,6 +72,26 @@ void QEMU_NORETURN cpu_loop_exit(CPUState *cpu);
 void QEMU_NORETURN cpu_loop_exit_restore(CPUState *cpu, uintptr_t pc);
 void QEMU_NORETURN cpu_loop_exit_atomic(CPUState *cpu, uintptr_t pc);
+ * cpu_cond_loop_exit_restore:
+ * @cpu: the vCPU state to be restored
+ * @pc: the host PC
+ *
+ * Trigger a cpu_loop_exit_restore() in case somebody asked for a return
+ * to the main loop (e.g. cpu_exit() or cpu_interrupt()).
+ *
+ * This is helpful for architectures that support interruptible
+ * instructions. After writing back all state to registers/memory, this
+ * call can be used to conditionally return back to the main loop or to
+ * continue executing the interruptible instruction.
+ */
+static inline void cpu_cond_loop_exit_restore(CPUState *cpu, uintptr_t pc)
+    if (unlikely((int32_t)atomic_read(&cpu_neg(cs)->icount_decr.u32) < 0)) {
+        cpu_loop_exit_restore(cs, ra);
+    }
 #if !defined(CONFIG_USER_ONLY)
 void cpu_reloading_memory_map(void);

Or, as alternative, something like "cpu_shall_exit()" which only
wraps the single check.



David / dhildenb

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