From 9b4e6f496601d3cd35fd8d09c9e2103999fd5c33 Mon Sep 17 00:00:00 2001 From: Paolo Bonzini Date: Tue, 11 Sep 2018 13:15:32 +0200 Subject: [PATCH] cpus: take seqlock across qemu_icount updates Even though writes of qemu_icount can safely race with reads in qemu_icount_raw, qemu_icount is also read by icount_adjust, which runs in the I/O thread. Therefore, writes do needs protection of the vm_clock_lock; for simplicity the patch protects it with both seqlock+spinlock, which we already do for hosts that lack 64-bit atomics. The bug actually predated the introduction of vm_clock_lock; cpu_update_icount would have needed the BQL before the spinlock was introduced. Reported-by: Emilio G. Cota Signed-off-by: Paolo Bonzini --- cpus.c | 22 ++++++++++++++-------- 1 file changed, 14 insertions(+), 8 deletions(-) diff --git a/cpus.c b/cpus.c index 4abc3b3dda..6e1a892f8c 100644 --- a/cpus.c +++ b/cpus.c @@ -245,21 +245,27 @@ static int64_t cpu_get_icount_executed(CPUState *cpu) * account executed instructions. This is done by the TCG vCPU * thread so the main-loop can see time has moved forward. */ -void cpu_update_icount(CPUState *cpu) +static void cpu_update_icount_locked(CPUState *cpu) { int64_t executed = cpu_get_icount_executed(cpu); cpu->icount_budget -= executed; -#ifndef CONFIG_ATOMIC64 - seqlock_write_lock(&timers_state.vm_clock_seqlock, - &timers_state.vm_clock_lock); -#endif atomic_set__nocheck(&timers_state.qemu_icount, timers_state.qemu_icount + executed); -#ifndef CONFIG_ATOMIC64 +} + +/* + * Update the global shared timer_state.qemu_icount to take into + * account executed instructions. This is done by the TCG vCPU + * thread so the main-loop can see time has moved forward. + */ +void cpu_update_icount(CPUState *cpu) +{ + seqlock_write_lock(&timers_state.vm_clock_seqlock, + &timers_state.vm_clock_lock); + cpu_update_icount_locked(cpu); seqlock_write_unlock(&timers_state.vm_clock_seqlock, &timers_state.vm_clock_lock); -#endif } static int64_t cpu_get_icount_raw_locked(void) @@ -272,7 +278,7 @@ static int64_t cpu_get_icount_raw_locked(void) exit(1); } /* Take into account what has run */ - cpu_update_icount(cpu); + cpu_update_icount_locked(cpu); } /* The read is protected by the seqlock, so __nocheck is okay. */ return atomic_read__nocheck(&timers_state.qemu_icount); -- 2.11.4.GIT