Date:   Wed, 21 Nov 2018 12:17:45 +0000
From:   Julien Thierry <julien.thierry@....com>
To:     Christoffer Dall <christoffer.dall@....com>, peng.hao2@....com.cn
Cc:     marc.zyngier@....com, andre.przywara@....com,
        linux-kernel@...r.kernel.org, leif.lindholm@...aro.org,
        ard.bieshseuvel@...aro.org, kvmarm@...ts.cs.columbia.edu,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] kvm: arm/arm64 : fix vm's hanging at startup time



On 21/11/18 11:06, Christoffer Dall wrote:
> Hi,
> 
> On Wed, Nov 21, 2018 at 04:56:54PM +0800, peng.hao2@....com.cn wrote:
>>> On 19/11/2018 09:10, Mark Rutland wrote:
>>>> On Sat, Nov 17, 2018 at 10:58:37AM +0800, peng.hao2@....com.cn wrote:
>>>>>> On 16/11/18 00:23, peng.hao2@....com.cn wrote:
>>>>>>>> Hi,
>>>>>>>>> When virtual machine starts, hang up.
>>>>>>>>
>>>>>>>> I take it you mean the *guest* hangs? Because it doesn't get a timer
>>>>>>>> interrupt?
>>>>>>>>
>>>>>>>>> The kernel version of guest
>>>>>>>>> is 4.16. Host support vgic_v3.
>>>>>>>>
>>>>>>>> Your host kernel is something recent, I guess?
>>>>>>>>
>>>>>>>>> It was mainly due to the incorrect vgic_irq's(intid=27) group value
>>>>>>>>> during injection interruption. when kvm_vgic_vcpu_init is called,
>>>>>>>>> dist is not initialized at this time. Unable to get vgic V3 or V2
>>>>>>>>> correctly, so group is not set.
>>>>>>>>
>>>>>>>> Mmh, that shouldn't happen with (v)GICv3. Do you use QEMU (which
>>>>>>>> version?) or some other userland tool?
>>>>>>>>
>>>>>>>
>>>>>>> QEMU emulator version 3.0.50 .
>>>>>>>
>>>>>>>>> group is setted to 1 when vgic_mmio_write_group is invoked at some
>>>>>>>>> time.
>>>>>>>>> when irq->group=0 (intid=27), No ICH_LR_GROUP flag was set and
>>>>>>>>> interrupt injection failed.
>>>>>>>>>
>>>>>>>>> Signed-off-by: Peng Hao <peng.hao2@....com.cn>
>>>>>>>>> ---
>>>>>>>>>    virt/kvm/arm/vgic/vgic-v3.c | 2 +-
>>>>>>>>>    1 file changed, 1 insertion(+), 1 deletion(-)
>>>>>>>>>
>>>>>>>>> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
>>>>>>>>> index 9c0dd23..d101000 100644
>>>>>>>>> --- a/virt/kvm/arm/vgic/vgic-v3.c
>>>>>>>>> +++ b/virt/kvm/arm/vgic/vgic-v3.c
>>>>>>>>> @@ -198,7 +198,7 @@ void vgic_v3_populate_lr(struct kvm_vcpu *vcpu,
>>>>>>>>> struct vgic_irq *irq, int lr) if (vgic_irq_is_mapped_level(irq) &&
>>>>>>>>> (val & ICH_LR_PENDING_BIT)) irq->line_level = false;
>>>>>>>>>
>>>>>>>>> -    if (irq->group)
>>>>>>>>> +    if (model == KVM_DEV_TYPE_ARM_VGIC_V3)
>>>>>>>>
>>>>>>>> This is not the right fix, not only because it basically reverts the
>>>>>>>> GICv3 part of 87322099052 (KVM: arm/arm64: vgic: Signal IRQs using
>>>>>>>> their configured group).
>>>>>>>>
>>>>>>>> Can you try to work out why kvm_vgic_vcpu_init() is apparently called
>>>>>>>> before dist->vgic_model is set, also what value it has?
>>>>>>>> If I understand the code correctly, that shouldn't happen for a GICv3.
>>>>>>>>
>>>>>>> Even if the value of  group is correctly assigned in kvm_vgic_vcpu_init, the group is then written 0 through vgic_mmio_write_group.
>>>>>>>    If the interrupt comes at this time, the interrupt injection fails.
>>>>>>
>>>>>> Does that mean that the guest is configuring its interrupts as Group0?
>>>>>> That sounds wrong, Linux should configure all it's interrupts as
>>>>>> non-secure group1.
>>>>>
>>>>> no, I think that uefi dose this, not linux.
>>>>> 1. kvm_vgic_vcpu_init
>>>>> 2. vgic_create
>>>>> 3. kvm_vgic_dist_init
>>>>> 4.vgic_mmio_write_group: uefi as guest, write group=0
>>>>> 5.vgic_mmio_write_group: linux as guest, write group=1
>>>>
>>>> Is this the same issue fixed by EDK2 commit:
>>>>
>>>> 66127011a544b90e ("ArmPkg/ArmGicDxe ARM: fix encoding for GICv3 interrupt acknowledge")
>>>>
>>>> ... where EDK2 would try to use IAR0 rather than IAR1?
>>>>
>>>> The commit messages notes this lead to a boot-time hang.
>>>
>>> I managed to trigger an issue with a really old EFI implementation that
>>> doesn't configure its interrupts as Group1, and yet tries to ACK its
>>> interrupts using the Group1 accessor. Guess what? It is not going to work.
>>>
>>> Commit c7fefb690661f2e38afcb8200bd318ecf38ab961 in the edk2 tree seems
>>> to be the fix (I only assume it does, I haven't actually checked). A
>>> recent build, as found in Debian Buster, works perfectly (tested with
>>> both QEMU v2.12 and tip of tree).
>>>
>>> Now, I really don't get what you're saying about Linux not getting
>>> interrupts. How do you get to booting Linux if EFI is not making any
>>> forward progress? Are you trying them independently?
>>>
>> I start linux with bypassing uefi, the print info is the same.
>> [507107.748908]  vgic_mmio_write_group:## intid/27 group=0
>> [507107.752185]  vgic_mmio_write_group:## intid/27 group=0
>> [507107.899566]  vgic_mmio_write_group:## intid/27 group=1
>> [507107.907370]  vgic_mmio_write_group:## intid/27 group=1
>> the command line is like this:
>> /home/qemu-patch/linshi/qemu/aarch64-softmmu/qemu-system-aarch64  -machine virt-3.1,accel=kvm,usb=off,dump-guest-core=off,gic-version=3  -kernel /home/kernelboot/vmlinuz-4.16.0+ -initrd /home/kernelboot/initramfs-4.16.0+.img -append root=/dev/mapper/cla-root ro crashkernel=auto rd.lvm.lv=cla/root rd.lvm.lv=cla/swap.UTF-8  -drive file=/home/centos74-ph/boot.qcow2,format=qcow2,if=none,id=drive-scsi0-0-0-0 -device scsi-hd,bus=scsi0.0,channel=0,scsi-id=0,lun=0,drive=drive-scsi0-0-0-0,id=scsi0-0-0-0,bootindex=1  -vnc 0.0.0.0:0 -k en-us -device virtio-gpu-pci,id=video0,max_outputs=1,bus=pci.3,addr=0x0 -device pvpanic-mmio -msg timestamp=on
>>
>> This is strange. That's probably the Linux 4.16  kernel setting group to 0, and I'll continue to track in guest.
> 
> Could you try the following patch:
> 
> diff --git a/virt/kvm/arm/vgic/vgic-init.c b/virt/kvm/arm/vgic/vgic-init.c
> index c0c0b88af1d5..6fa858c7a5a6 100644
> --- a/virt/kvm/arm/vgic/vgic-init.c
> +++ b/virt/kvm/arm/vgic/vgic-init.c
> @@ -231,13 +231,6 @@ int kvm_vgic_vcpu_init(struct kvm_vcpu *vcpu)
>   			irq->config = VGIC_CONFIG_LEVEL;
>   		}
>   
> -		/*
> -		 * GICv3 can only be created via the KVM_DEVICE_CREATE API and
> -		 * so we always know the emulation type at this point as it's
> -		 * either explicitly configured as GICv3, or explicitly
> -		 * configured as GICv2, or not configured yet which also
> -		 * implies GICv2.
> -		 */
>   		if (dist->vgic_model == KVM_DEV_TYPE_ARM_VGIC_V3)
>   			irq->group = 1;
>   		else
> @@ -298,6 +291,16 @@ int vgic_init(struct kvm *kvm)
>   	if (ret)
>   		goto out;
>   
> +	/* Initialize groups on CPUs created before the VGIC type was known */
> +	kvm_for_each_vcpu(i, vcpu, kvm) {
> +		struct vgic_cpu *vgic_cpu = &vcpu->arch.vgic_cpu;
> +
> +		for (i = 0; i < VGIC_NR_PRIVATE_IRQS; i++) {
> +			struct vgic_irq *irq = &vgic_cpu->private_irqs[i];
> +			irq->group = 1;
> +		}
> +	}
> +
>   	if (vgic_has_its(kvm)) {
>   		ret = vgic_v4_init(kvm);
>   		if (ret)
> 
> 

If the value of dist->vgic_model is not properly initialized at the time 
we call kvm_vgic_vcpu_init is call, won't we still overwrite the 
irq->group when we get there? (I still haven't seen why we could 
consider dist->vgic_model is initialized at that point).

Shouldn't we do the irq->group initialization somewhere in 
kvm_arch_vcpu_ioctl_vcpu_init? (with some vgic_* function to encapsulate 
it of course). At that point I believe we know that dist->vgic_model is 
initialized.

Cheers,

-- 
Julien Thierry

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