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cpu-exec: fix missed CPU kick during interrupt injection

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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 <david@redhat.com>
Message-Id: <20171129191319.11483-1-david@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
David Hildenbrand 2017-11-29 20:13:19 +01:00 committed by Paolo Bonzini
parent ebd05fea9b
commit d84be02d69
1 changed files with 3 additions and 9 deletions
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12
accel/tcg/cpu-exec.c
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@ -525,19 +525,13 @@ static inline bool cpu_handle_interrupt(CPUState *cpu,
TranslationBlock **last_tb) TranslationBlock **last_tb)
{ {
CPUClass *cc = CPU_GET_CLASS(cpu); CPUClass *cc = CPU_GET_CLASS(cpu);
int32_t insns_left;
/* Clear the interrupt flag now since we're processing /* Clear the interrupt flag now since we're processing
* cpu->interrupt_request and cpu->exit_request. * 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_mb_set(&cpu->icount_decr.u16.high, 0);
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();
}
if (unlikely(atomic_read(&cpu->interrupt_request))) { if (unlikely(atomic_read(&cpu->interrupt_request))) {
int interrupt_request; int interrupt_request;