| Message ID | 20180404135052.jsduo4s4pxoelnn6@linutronix.de (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On 2018-04-04 15:50:52 [+0200], To kvmarm@lists.cs.columbia.edu wrote:
already applied as
5a2457503297 ("KVM: arm/arm64: Remove redundant preemptible checks")
Sebastian
diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c index 3db4af5d0197..60a3f23927d9 100644 --- a/virt/kvm/arm/arm.c +++ b/virt/kvm/arm/arm.c @@ -69,7 +69,6 @@ static DEFINE_PER_CPU(unsigned char, kvm_arm_hardware_enabled); static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu) { - BUG_ON(preemptible()); __this_cpu_write(kvm_arm_running_vcpu, vcpu); } @@ -79,7 +78,6 @@ static void kvm_arm_set_running_vcpu(struct kvm_vcpu *vcpu) */ struct kvm_vcpu *kvm_arm_get_running_vcpu(void) { - BUG_ON(preemptible()); return __this_cpu_read(kvm_arm_running_vcpu); }
native KVM crashes on -RT: |------------[ cut here ]------------ |kernel BUG virt/kvm/arm/arm.c:82! |Internal error: Oops - BUG: 0 [#1] PREEMPT SMP |Modules linked in: |CPU: 3 PID: 1527 Comm: qemu-system-aar Tainted: G W 4.14.29-rt25+ #48 |Hardware name: Freescale Layerscape 2088A RDB Board (DT) |PC is at kvm_arm_get_running_vcpu+0x48/0x50 |LR is at vgic_mmio_change_active.isra.1+0x2c/0xe0 |Process qemu-system-aar (pid: 1527, stack limit = 0xffff0000128c8000) |Call trace: | kvm_arm_get_running_vcpu+0x48/0x50 | vgic_mmio_change_active.isra.1+0x2c/0xe0 | __vgic_mmio_write_cactive+0x7c/0xd0 | vgic_mmio_uaccess_write_cactive+0xc/0x18 | vgic_uaccess+0xac/0xd8 | vgic_v2_dist_uaccess+0x3c/0x48 | vgic_v2_attr_regs_access.isra.3+0x144/0x158 | vgic_v2_set_attr+0xbc/0xe0 | kvm_device_ioctl_attr+0x80/0xb0 | kvm_device_ioctl+0x60/0xa8 | do_vfs_ioctl+0xa4/0xa18 | SyS_ioctl+0x44/0x80 vgic_mmio_change_active() holds &irq->irq_lock spin lock which makes context not-preemptible. On -RT the same lock is a sleeping lock and thus it remains preemptible but can not be migrated to another CPU. I *think* that the BUG() statement in kvm_arm_get_running_vcpu() is to ensure that we don't switch CPUs while accessing per-CPU variables. __this_cpu_write() + __this_cpu_read() will trigger a warning (with CONFIG_DEBUG_PREEMPT enabled) to spot such usage without crashing the whole machine. Therefore I suggest to remove this check. Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- virt/kvm/arm/arm.c | 2 -- 1 file changed, 2 deletions(-)