From d84be02d69a23dea249f351324d497f613994129 Mon Sep 17 00:00:00 2001 From: David Hildenbrand Date: Wed, 29 Nov 2017 20:13:19 +0100 Subject: cpu-exec: fix missed CPU kick during interrupt injection The conditional memory barrier not only looks strange but actually is wrong. On s390x, I can reproduce interrupts via cpu_interrupt() not leading to a proper kick out of emulation every now and then. cpu_interrupt() is especially used for inter CPU communication via SIGP (esp. external calls and emergency interrupts). With this patch, I was not able to reproduce. (esp. no stalls or hangs in the guest). My setup is s390x MTTCG with 16 VCPUs on 8 CPU host, running make -j16. Signed-off-by: David Hildenbrand Message-Id: <20171129191319.11483-1-david@redhat.com> Signed-off-by: Paolo Bonzini --- accel/tcg/cpu-exec.c | 12 +++--------- 1 file changed, 3 insertions(+), 9 deletions(-) (limited to 'accel') diff --git a/accel/tcg/cpu-exec.c b/accel/tcg/cpu-exec.c index 9b544d88c8..4452cd9856 100644 --- a/accel/tcg/cpu-exec.c +++ b/accel/tcg/cpu-exec.c @@ -525,19 +525,13 @@ static inline bool cpu_handle_interrupt(CPUState *cpu, TranslationBlock **last_tb) { CPUClass *cc = CPU_GET_CLASS(cpu); - int32_t insns_left; /* Clear the interrupt flag now since we're processing * cpu->interrupt_request and cpu->exit_request. + * Ensure zeroing happens before reading cpu->exit_request or + * cpu->interrupt_request (see also smp_wmb in cpu_exit()) */ - insns_left = atomic_read(&cpu->icount_decr.u32); - atomic_set(&cpu->icount_decr.u16.high, 0); - if (unlikely(insns_left < 0)) { - /* Ensure the zeroing of icount_decr comes before the next read - * of cpu->exit_request or cpu->interrupt_request. - */ - smp_mb(); - } + atomic_mb_set(&cpu->icount_decr.u16.high, 0); if (unlikely(atomic_read(&cpu->interrupt_request))) { int interrupt_request; -- cgit v1.2.1