Re: [RFC PATCH 2/3] kvm: arm/arm64: vgic-vits: free its resource when vm reboot/reset

Auger Eric
2017-09-13T08:46:58Z

Hi Wanghaibin,

On 12/09/2017 13:15, wanghaibin wrote:
> On 2017/9/11 2:46, Auger Eric wrote:
>
>> Hi Wanghaibin,
>>
>> On 07/09/2017 13:28, Auger Eric wrote:
>>> Hi Wanghaibin,
>>>
>>> On 07/09/2017 03:32, wanghaibin wrote:
>>>> On 2017/9/7 0:20, Auger Eric wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> On 06/09/2017 15:05, wanghaibin wrote:
>>>>>> This patch fix the migrate save tables failure.
>>>>>>
>>>>>> When the virtual machine is in booting and the devices haven't initialized,
>>>>>> the all virtual dte/ite may be invalid. If migrate at this moment, the save
>>>>>> tables interface traversal device list, and check the dte is valid or not.
>>>>>> if not, it will return the -EINVAL.
>>>>>
>>>>> The issue on save is less clear to me. We are not checking the "dte" are
>>>>> valid as it is said above. We are scrolling the ITS lists - which may be
>>>>> empty - and dump them in guest memory.
>>>>>
>>>>> On save() there are quite few checks that can cause a failure.
>>>>> vgic_its_check_id() can be among them. This typically requires the
>>>>> GITS_BASER to have been properly set. Failing on save looks OK to me in
>>>>> such situation.
>>>>>
>>>>> Sorry but I don't get the purpose of this patch. Does it fix a save failure?
>>>>
>>>>
>>>> Yes, for save, vgic_its_check_id() func will check the L1 DTE valid or not through
>>>> the code like :
>>>>
>>>> /* Each 1st level entry is represented by a 64-bit value. */
>>>> if (kvm_read_guest(its->dev->kvm,
>>>> BASER_ADDRESS(baser) + index * sizeof(indirect_ptr),
>>>> &indirect_ptr, sizeof(indirect_ptr)))
>>>> return false;
>>>>
>>>> indirect_ptr = le64_to_cpu(indirect_ptr);
>>>>
>>>> /* check the valid bit of the first level entry */
>>>> if (!(indirect_ptr & BIT_ULL(63)))
>>>> return false;
>>>>
>>>> If invalid , the save will return -EINVAL caused by the vgic_its_check_id() with return the false value.
>>>>
>>>> And form the cover letter, the problem happened when no one pci dev has been probed( guest driver haven't any
>>>> mapd, mapti), So the L1 DTEs are all invalid currently. Just like you said, at this moment migrate, we are scrolling
>>>> the ITS lists, next time check_id failed and save interface failed.
>>>>
>>>> I think the final reason is the device list free problem, at the reset/reboot, ITS dev/clo/itt lists are not be free
>>>> and set NULL. So that, the save interface failed.
>>>> This patch try to free the resource when vm reboot/reset.
>>> OK understood. Indeed none of the device/collection lists should be non
>>> empty at that stage, ie. when GITS_BASERn have not be written yet and
>>> are marked invalid.
>>>
>>> For solving the specific save() issue here, I think the best is to check
>>> the validity bit of the GITS_BASER (col, device) and if invalid do nothing.
>>
>> Actually the above proposal does not work as GITS_BASERn is not properly
>> reset. Maybe the best way is to introduce an ITS KVM device reset IOTCL
>> in the control group. Upon this command we could properly reset the
>> requested registers and the lists.
>
>
> Yes, It should free these lists when vits reset.
>
> This patch according the has_run_once and vcpu_init to mark the vcpu reset happened,
> and scrolling all kvm devices to find the vits device to free the lists.
> I think it's a little odd too.
>
> If we can add the reset IOCTL, I think it must be the best way.

I looked at the qemu reset of the GICv3 and my understanding is the QEMU
reset function sends reset values for each individual register. So my
understanding is I should align QEMU ITS reset code. Then, we should
free internal lists in the relevant register write when detecting the
valid bit is not set.
>
> Thanks.
>
>>
>> Thanks
>>
>> Eric
>>>
>>> Then we need to have a more global discussion about whether, when and
>>> where the device and collection lists need to be freed.
>>>
>>> If you want I can respin with above suggestion and add the valid pointer
>>> to the entry_fn_t to handle the restore path. Up to you.
>
>
> All along, I want to contribute code to the community, so far, It has not been achieved.
> So I would like to collect the solutions for this problem and try to fix it first, can I?
OK sure. So I will send a QEMU patch today and I will review your kernel
fixes then.

Thanks

Eric
>
> Thanks.
>
>>>
>>> Thanks
>>>
>>> Eric
>>>
>>>
>>>> BTW: these lists will re-bulid when the reboot vm run the probe pci device step.
>>>
>>>>
>>>> Thanks
>>>>
>>>>>
>>>>> Thanks
>>>>>
>>>>> Eric
>>>>>
>>>>>
>>>>>>
>>>>>> This patch try to free the its list resource when vm reboot or reset to avoid this.
>>>>>>
>>>>>> Signed-off-by: wanghaibin <wanghaibin.wang@huawei.com>
>>>>>> ---
>>>>>> virt/kvm/arm/arm.c | 5 ++++-
>>>>>> virt/kvm/arm/vgic/vgic-its.c | 10 ++++++++++
>>>>>> virt/kvm/arm/vgic/vgic.h | 1 +
>>>>>> 3 files changed, 15 insertions(+), 1 deletion(-)
>>>>>>
>>>>>> diff --git a/virt/kvm/arm/arm.c b/virt/kvm/arm/arm.c
>>>>>> index a39a1e1..db7632d 100644
>>>>>> --- a/virt/kvm/arm/arm.c
>>>>>> +++ b/virt/kvm/arm/arm.c
>>>>>> @@ -46,6 +46,7 @@
>>>>>> #include <asm/kvm_coproc.h>
>>>>>> #include <asm/kvm_psci.h>
>>>>>> #include <asm/sections.h>
>>>>>> +#include "vgic.h"
>>>>>>
>>>>>> #ifdef REQUIRES_VIRT
>>>>>> __asm__(".arch_extension virt");
>>>>>> @@ -901,8 +902,10 @@ static int kvm_arch_vcpu_ioctl_vcpu_init(struct kvm_vcpu *vcpu,
>>>>>> * Ensure a rebooted VM will fault in RAM pages and detect if the
>>>>>> * guest MMU is turned off and flush the caches as needed.
>>>>>> */
>>>>>> - if (vcpu->arch.has_run_once)
>>>>>> + if (vcpu->arch.has_run_once) {
>>>>>> stage2_unmap_vm(vcpu->kvm);
>>>>>> + vgic_its_free_resource(vcpu->kvm);
>>>>>> + }
>>>>>>
>>>>>> vcpu_reset_hcr(vcpu);
>>>>>>
>>>>>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>>>>>> index 25d614f..5c20352 100644
>>>>>> --- a/virt/kvm/arm/vgic/vgic-its.c
>>>>>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>>>>>> @@ -2467,6 +2467,16 @@ static int vgic_its_get_attr(struct kvm_device *dev,
>>>>>> .has_attr = vgic_its_has_attr,
>>>>>> };
>>>>>>
>>>>>> +void vgic_its_free_resource(struct kvm *kvm)
>>>>>> +{
>>>>>> + struct kvm_device *dev, *tmp;
>>>>>> +
>>>>>> + list_for_each_entry_safe(dev, tmp, &kvm->devices, vm_node) {
>>>>>> + if(dev->ops == &kvm_arm_vgic_its_ops)
>>>>>> + vgic_its_free_list(kvm, dev->private);
>>>>>> + }
>>>>>> +}
>>>>>> +
>>>>>> int kvm_vgic_register_its_device(void)
>>>>>> {
>>>>>> return kvm_register_device_ops(&kvm_arm_vgic_its_ops,
>>>>>> diff --git a/virt/kvm/arm/vgic/vgic.h b/virt/kvm/arm/vgic/vgic.h
>>>>>> index c2be5b7..fbcbdfd 100644
>>>>>> --- a/virt/kvm/arm/vgic/vgic.h
>>>>>> +++ b/virt/kvm/arm/vgic/vgic.h
>>>>>> @@ -222,5 +222,6 @@ int vgic_v3_line_level_info_uaccess(struct kvm_vcpu *vcpu, bool is_write,
>>>>>>
>>>>>> bool lock_all_vcpus(struct kvm *kvm);
>>>>>> void unlock_all_vcpus(struct kvm *kvm);
>>>>>> +void vgic_its_free_resource(struct kvm *kvm);
>>>>>>
>>>>>> #endif
>>>>>>
>>>>>
>>>>> .
>>>>>
>>>>
>>>>
>>>>
>>
>> .
>>
>
>
>