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| author | Matt T. Yourst <yourst@users.sourceforge.net> | 2009-02-24 15:28:00 -0300 |
|---|---|---|
| committer | Avi Kivity <avi@redhat.com> | 2009-06-10 11:48:24 +0300 |
| commit | 2dea4c84bc936731668b5a7a9fba5b436a422668 (patch) | |
| tree | f0679d55a34a960b20b0ad8bce35cccf497488d6 /arch/x86/kvm/x86.c | |
| parent | d510d6cc653bc4b3094ea73afe12600d0ab445b3 (diff) | |
| download | lwn-2dea4c84bc936731668b5a7a9fba5b436a422668.tar.gz lwn-2dea4c84bc936731668b5a7a9fba5b436a422668.zip | |
KVM: x86: silence preempt warning on kvm_write_guest_time
This issue just appeared in kvm-84 when running on 2.6.28.7 (x86-64)
with PREEMPT enabled.
We're getting syslog warnings like this many (but not all) times qemu
tells KVM to run the VCPU:
BUG: using smp_processor_id() in preemptible [00000000] code:
qemu-system-x86/28938
caller is kvm_arch_vcpu_ioctl_run+0x5d1/0xc70 [kvm]
Pid: 28938, comm: qemu-system-x86 2.6.28.7-mtyrel-64bit
Call Trace:
debug_smp_processor_id+0xf7/0x100
kvm_arch_vcpu_ioctl_run+0x5d1/0xc70 [kvm]
? __wake_up+0x4e/0x70
? wake_futex+0x27/0x40
kvm_vcpu_ioctl+0x2e9/0x5a0 [kvm]
enqueue_hrtimer+0x8a/0x110
_spin_unlock_irqrestore+0x27/0x50
vfs_ioctl+0x31/0xa0
do_vfs_ioctl+0x74/0x480
sys_futex+0xb4/0x140
sys_ioctl+0x99/0xa0
system_call_fastpath+0x16/0x1b
As it turns out, the call trace is messed up due to gcc's inlining, but
I isolated the problem anyway: kvm_write_guest_time() is being used in a
non-thread-safe manner on preemptable kernels.
Basically kvm_write_guest_time()'s body needs to be surrounded by
preempt_disable() and preempt_enable(), since the kernel won't let us
query any per-CPU data (indirectly using smp_processor_id()) without
preemption disabled. The attached patch fixes this issue by disabling
preemption inside kvm_write_guest_time().
[marcelo: surround only __get_cpu_var calls since the warning
is harmless]
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'arch/x86/kvm/x86.c')
| -rw-r--r-- | arch/x86/kvm/x86.c | 2 |
1 files changed, 2 insertions, 0 deletions
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3944e917e794..43e049a2ccf4 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -634,10 +634,12 @@ static void kvm_write_guest_time(struct kvm_vcpu *v) if ((!vcpu->time_page)) return; + preempt_disable(); if (unlikely(vcpu->hv_clock_tsc_khz != __get_cpu_var(cpu_tsc_khz))) { kvm_set_time_scale(__get_cpu_var(cpu_tsc_khz), &vcpu->hv_clock); vcpu->hv_clock_tsc_khz = __get_cpu_var(cpu_tsc_khz); } + preempt_enable(); /* Keep irq disabled to prevent changes to the clock */ local_irq_save(flags); |