Messages in this thread Patch in this message | | | Date | Wed, 18 Jan 2023 11:54:02 +0000 | From | Marc Zyngier <> | Subject | Re: [PATCH] KVM: arm64: vgic: Fix soft lockup during VM teardown |
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Shanker,
Please Cc all the KVM/arm64 reviewers when sending KVM/arm64 patches.
On Wed, 18 Jan 2023 02:23:48 +0000, Shanker Donthineni <sdonthineni@nvidia.com> wrote: > > Getting intermittent CPU soft lockups during the virtual machines > teardown on a system with GICv4 features enabled. The function > __synchronize_hardirq() has been waiting for IRQD_IRQ_INPROGRESS > to be cleared forever as per the current implementation. > > CPU stuck here for a long time leads to soft lockup: > while (irqd_irq_inprogress(&desc->irq_data)) > cpu_relax();
Is it a soft-lockup from which the system recovers? or a livelock which leaves the system dead?
What kernel version is that? Please provide all the relevant context that could help analysing the issue.
> > Call trace from the lockup CPU: > [ 87.238866] watchdog: BUG: soft lockup - CPU#37 stuck for 23s! > [ 87.250025] CPU: 37 PID: 1031 Comm: qemu-system-aarch64 > [ 87.358397] Call trace: > [ 87.360891] __synchronize_hardirq+0x48/0x140 > [ 87.365343] free_irq+0x138/0x424 > [ 87.368727] vgic_v4_teardown+0xa4/0xe0 > [ 87.372649] __kvm_vgic_destroy+0x18c/0x194 > [ 87.376922] kvm_vgic_destroy+0x28/0x3c > [ 87.380839] kvm_arch_destroy_vm+0x24/0x44 > [ 87.385024] kvm_destroy_vm+0x158/0x2c4 > [ 87.388943] kvm_vm_release+0x6c/0x98 > [ 87.392681] __fput+0x70/0x220 > [ 87.395800] ____fput+0x10/0x20 > [ 87.399005] task_work_run+0xb4/0x23c > [ 87.402746] do_exit+0x2bc/0x8a4 > [ 87.406042] do_group_exit+0x34/0xb0 > [ 87.409693] get_signal+0x878/0x8a0 > [ 87.413254] do_notify_resume+0x138/0x1530 > [ 87.417440] el0_svc+0xdc/0xf0 > [ 87.420559] el0t_64_sync_handler+0xf0/0x11c > [ 87.424919] el0t_64_sync+0x18c/0x190 > > The state of the IRQD_IRQ_INPROGRESS information is lost inside > irq_domain_activate_irq() which happens before calling free_irq(). > Instrumented the code and confirmed, the IRQD state is changed from > 0x10401400 to 0x10441600 instead of 0x10401600 causing problem. > > Call trace from irqd_set_activated(): > [ 78.983544] irqd_set_activated: lost IRQD_IRQ_INPROGRESS > old=0x10401400, new=0x10441600 > [ 78.992093] CPU: 19 PID: 1511 Comm: qemu-system-aarch64 > [ 79.008461] Call trace: > [ 79.010956] dump_backtrace.part.0+0xc8/0xe0 > [ 79.015328] show_stack+0x18/0x54 > [ 79.018713] dump_stack_lvl+0x64/0x7c > [ 79.022459] dump_stack+0x18/0x30 > [ 79.025842] irq_domain_activate_irq+0x88/0x94 > [ 79.030385] vgic_v3_save_pending_tables+0x260/0x29c > [ 79.035463] vgic_set_common_attr+0xac/0x23c > [ 79.039826] vgic_v3_set_attr+0x48/0x60 > [ 79.043742] kvm_device_ioctl+0x120/0x19c > [ 79.047840] __arm64_sys_ioctl+0x42c/0xe00 > [ 79.052027] invoke_syscall.constprop.0+0x50/0xe0 > [ 79.056835] do_el0_svc+0x58/0x180 > [ 79.060308] el0_svc+0x38/0xf0 > [ 79.063425] el0t_64_sync_handler+0xf0/0x11c > [ 79.067785] el0t_64_sync+0x18c/0x190
Are these two traces an indication of concurrent events? Or are they far apart?
> > irqreturn_t handle_irq_event(struct irq_desc *desc) > { > irqd_set(&desc->irq_data, IRQD_IRQ_INPROGRESS); > raw_spin_unlock(&desc->lock); > > ret = handle_irq_event_percpu(desc); > > raw_spin_lock(&desc->lock); > irqd_clear(&desc->irq_data, IRQD_IRQ_INPROGRESS); > }
How is that relevant to this trace? Do you see this function running concurrently with the teardown? If it matters here, it must be a VPE doorbell, right? But you claim that this is on a GICv4 platform, while this would only affect GICv4.1... Or are you using GICv4.1?
> > In this particular failed case and based on traces, the two functions > irqd_set_activated() and handle_irq_event() are concurrently modifying > IRQD state without both holding desc->lock. The irqd_set_activated() > execution path is reading memory 'state_use_accessors' in between set > & clear of IRQD_IRQ_INPROGRESS state change and writing the modified > data after executing 'irqd_clear(desc->irq_data, IRQD_IRQ_INPROGRESS)'. > > To fix the lockup issue, hold desc->lock when calling functions > irq_domain_activate_irq() and irq_domain_deactivate_irq).
For that particular issue, the main problem is that we are abusing the interrupt startup/teardown code. The locking is only a consequence of this.
> > Signed-off-by: Shanker Donthineni <sdonthineni@nvidia.com> > --- > arch/arm64/kvm/vgic/vgic-v3.c | 6 ++++++ > arch/arm64/kvm/vgic/vgic-v4.c | 4 ++++ > 2 files changed, 10 insertions(+) > > diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c > index 2074521d4a8c..e6aa909fcbe2 100644 > --- a/arch/arm64/kvm/vgic/vgic-v3.c > +++ b/arch/arm64/kvm/vgic/vgic-v3.c > @@ -353,22 +353,28 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq) > static void unmap_all_vpes(struct vgic_dist *dist) > { > struct irq_desc *desc; > + unsigned long flags; > int i; > > for (i = 0; i < dist->its_vm.nr_vpes; i++) { > desc = irq_to_desc(dist->its_vm.vpes[i]->irq); > + raw_spin_lock_irqsave(&desc->lock, flags); > irq_domain_deactivate_irq(irq_desc_get_irq_data(desc)); > + raw_spin_unlock_irqrestore(&desc->lock, flags);
I guess this is the guilty one, based on your analysis, and assuming this is a v4.1 issue, not v4.
> } > } > > static void map_all_vpes(struct vgic_dist *dist) > { > struct irq_desc *desc; > + unsigned long flags; > int i; > > for (i = 0; i < dist->its_vm.nr_vpes; i++) { > desc = irq_to_desc(dist->its_vm.vpes[i]->irq); > + raw_spin_lock_irqsave(&desc->lock, flags); > irq_domain_activate_irq(irq_desc_get_irq_data(desc), false); > + raw_spin_unlock_irqrestore(&desc->lock, flags); > } > } > > diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c > index ad06ba6c9b00..a01b8313e82c 100644 > --- a/arch/arm64/kvm/vgic/vgic-v4.c > +++ b/arch/arm64/kvm/vgic/vgic-v4.c > @@ -139,8 +139,10 @@ static void vgic_v4_enable_vsgis(struct kvm_vcpu *vcpu) > /* Transfer the full irq state to the vPE */ > vgic_v4_sync_sgi_config(vpe, irq); > desc = irq_to_desc(irq->host_irq); > + raw_spin_lock(&desc->lock); > ret = irq_domain_activate_irq(irq_desc_get_irq_data(desc), > false); > + raw_spin_unlock(&desc->lock);
This one looks wrong. The interrupt never fires on the host (that's the whole point of this stuff). There isn't even a handler attached to it. How can that result in a problem?
My take on the whole thing is that we should stop playing games with the underlying interrupt infrastructure. How about the following hack, which is only compile-tested. Let me know if that helps.
M.
diff --git a/arch/arm64/kvm/vgic/vgic-v3.c b/arch/arm64/kvm/vgic/vgic-v3.c index 2074521d4a8c..2624963cb95b 100644 --- a/arch/arm64/kvm/vgic/vgic-v3.c +++ b/arch/arm64/kvm/vgic/vgic-v3.c @@ -350,26 +350,23 @@ int vgic_v3_lpi_sync_pending_status(struct kvm *kvm, struct vgic_irq *irq) * The deactivation of the doorbell interrupt will trigger the * unmapping of the associated vPE. */ -static void unmap_all_vpes(struct vgic_dist *dist) +static void unmap_all_vpes(struct kvm *kvm) { - struct irq_desc *desc; + struct vgic_dist *dist = &kvm->arch.vgic; int i; - for (i = 0; i < dist->its_vm.nr_vpes; i++) { - desc = irq_to_desc(dist->its_vm.vpes[i]->irq); - irq_domain_deactivate_irq(irq_desc_get_irq_data(desc)); - } + for (i = 0; i < dist->its_vm.nr_vpes; i++) + free_irq(dist->its_vm.vpes[i]->irq, kvm_get_vcpu(kvm, i)); } -static void map_all_vpes(struct vgic_dist *dist) +static void map_all_vpes(struct kvm *kvm) { - struct irq_desc *desc; + struct vgic_dist *dist = &kvm->arch.vgic; int i; - for (i = 0; i < dist->its_vm.nr_vpes; i++) { - desc = irq_to_desc(dist->its_vm.vpes[i]->irq); - irq_domain_activate_irq(irq_desc_get_irq_data(desc), false); - } + for (i = 0; i < dist->its_vm.nr_vpes; i++) + WARN_ON(vgic_v4_request_vpe_irq(kvm_get_vcpu(kvm, i), + dist->its_vm.vpes[i]->irq)); } /** @@ -394,7 +391,7 @@ int vgic_v3_save_pending_tables(struct kvm *kvm) * and enabling of the doorbells have already been done. */ if (kvm_vgic_global_state.has_gicv4_1) { - unmap_all_vpes(dist); + unmap_all_vpes(kvm); vlpi_avail = true; } @@ -444,7 +441,7 @@ int vgic_v3_save_pending_tables(struct kvm *kvm) out: if (vlpi_avail) - map_all_vpes(dist); + map_all_vpes(kvm); return ret; } diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c index ad06ba6c9b00..a413718be92b 100644 --- a/arch/arm64/kvm/vgic/vgic-v4.c +++ b/arch/arm64/kvm/vgic/vgic-v4.c @@ -222,6 +222,11 @@ void vgic_v4_get_vlpi_state(struct vgic_irq *irq, bool *val) *val = !!(*ptr & mask); } +int vgic_v4_request_vpe_irq(struct kvm_vcpu *vcpu, int irq) +{ + return request_irq(irq, vgic_v4_doorbell_handler, 0, "vcpu", vcpu); +} + /** * vgic_v4_init - Initialize the GICv4 data structures * @kvm: Pointer to the VM being initialized @@ -283,8 +288,7 @@ int vgic_v4_init(struct kvm *kvm) irq_flags &= ~IRQ_NOAUTOEN; irq_set_status_flags(irq, irq_flags); - ret = request_irq(irq, vgic_v4_doorbell_handler, - 0, "vcpu", vcpu); + ret = vgic_v4_request_vpe_irq(vcpu, irq); if (ret) { kvm_err("failed to allocate vcpu IRQ%d\n", irq); /* diff --git a/arch/arm64/kvm/vgic/vgic.h b/arch/arm64/kvm/vgic/vgic.h index 0c8da72953f0..23e280fa0a16 100644 --- a/arch/arm64/kvm/vgic/vgic.h +++ b/arch/arm64/kvm/vgic/vgic.h @@ -331,5 +331,6 @@ int vgic_v4_init(struct kvm *kvm); void vgic_v4_teardown(struct kvm *kvm); void vgic_v4_configure_vsgis(struct kvm *kvm); void vgic_v4_get_vlpi_state(struct vgic_irq *irq, bool *val); +int vgic_v4_request_vpe_irq(struct kvm_vcpu *vcpu, int irq); #endif -- Without deviation from the norm, progress is not possible.
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