[RFC] vhost: Clear the pending messages on vhost_init_device_iotlb()

  When the vhost iotlb is used along with a guest virtual iommu
and the guest gets rebooted, some MISS messages may have been
recorded just before the reboot and spuriously executed by
the virtual iommu after the reboot. Despite the device iotlb gets
re-initialized, the messages are not cleared. Fix that by calling
vhost_clear_msg() at the end of vhost_init_device_iotlb().

Signed-off-by: Eric Auger <eric.auger@redhat.com>
---
 drivers/vhost/vhost.c | 1 +
 1 file changed, 1 insertion(+)
  

On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> When the vhost iotlb is used along with a guest virtual iommu
> and the guest gets rebooted, some MISS messages may have been
> recorded just before the reboot and spuriously executed by
> the virtual iommu after the reboot. Despite the device iotlb gets
> re-initialized, the messages are not cleared. Fix that by calling
> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> 
> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> ---
>  drivers/vhost/vhost.c | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> index 40097826cff0..422a1fdee0ca 100644
> --- a/drivers/vhost/vhost.c
> +++ b/drivers/vhost/vhost.c
> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>  	}
>  
>  	vhost_iotlb_free(oiotlb);
> +	vhost_clear_msg(d);
>  
>  	return 0;
>  }

Hmm.  Can't messages meanwhile get processes and affect the
new iotlb?


> -- 
> 2.37.3
  

Hi Michael,
On 11/7/22 21:42, Michael S. Tsirkin wrote:
> On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
>> When the vhost iotlb is used along with a guest virtual iommu
>> and the guest gets rebooted, some MISS messages may have been
>> recorded just before the reboot and spuriously executed by
>> the virtual iommu after the reboot. Despite the device iotlb gets
>> re-initialized, the messages are not cleared. Fix that by calling
>> vhost_clear_msg() at the end of vhost_init_device_iotlb().
>>
>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>> ---
>>  drivers/vhost/vhost.c | 1 +
>>  1 file changed, 1 insertion(+)
>>
>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>> index 40097826cff0..422a1fdee0ca 100644
>> --- a/drivers/vhost/vhost.c
>> +++ b/drivers/vhost/vhost.c
>> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>>  	}
>>  
>>  	vhost_iotlb_free(oiotlb);
>> +	vhost_clear_msg(d);
>>  
>>  	return 0;
>>  }
> Hmm.  Can't messages meanwhile get processes and affect the
> new iotlb?
Isn't the msg processing stopped at the moment this function is called
(VHOST_SET_FEATURES)?

Thanks

Eric
>
>
>> -- 
>> 2.37.3
  

On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> Hi Michael,
> On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> >> When the vhost iotlb is used along with a guest virtual iommu
> >> and the guest gets rebooted, some MISS messages may have been
> >> recorded just before the reboot and spuriously executed by
> >> the virtual iommu after the reboot. Despite the device iotlb gets
> >> re-initialized, the messages are not cleared. Fix that by calling
> >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> >>
> >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >> ---
> >>  drivers/vhost/vhost.c | 1 +
> >>  1 file changed, 1 insertion(+)
> >>
> >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >> index 40097826cff0..422a1fdee0ca 100644
> >> --- a/drivers/vhost/vhost.c
> >> +++ b/drivers/vhost/vhost.c
> >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> >>  	}
> >>  
> >>  	vhost_iotlb_free(oiotlb);
> >> +	vhost_clear_msg(d);
> >>  
> >>  	return 0;
> >>  }
> > Hmm.  Can't messages meanwhile get processes and affect the
> > new iotlb?
> Isn't the msg processing stopped at the moment this function is called
> (VHOST_SET_FEATURES)?
> 
> Thanks
> 
> Eric

It's pretty late here I'm not sure.  You tell me what prevents it.

BTW vhost_init_device_iotlb gets enabled parameter but ignores
it, we really should drop that.

Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
and then cleared, iotlb is not properly cleared - bug?


> >
> >
> >> -- 
> >> 2.37.3
  

On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> > Hi Michael,
> > On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> > >> When the vhost iotlb is used along with a guest virtual iommu
> > >> and the guest gets rebooted, some MISS messages may have been
> > >> recorded just before the reboot and spuriously executed by
> > >> the virtual iommu after the reboot. Despite the device iotlb gets
> > >> re-initialized, the messages are not cleared. Fix that by calling
> > >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> > >>
> > >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > >> ---
> > >>  drivers/vhost/vhost.c | 1 +
> > >>  1 file changed, 1 insertion(+)
> > >>
> > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > >> index 40097826cff0..422a1fdee0ca 100644
> > >> --- a/drivers/vhost/vhost.c
> > >> +++ b/drivers/vhost/vhost.c
> > >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> > >>    }
> > >>
> > >>    vhost_iotlb_free(oiotlb);
> > >> +  vhost_clear_msg(d);
> > >>
> > >>    return 0;
> > >>  }
> > > Hmm.  Can't messages meanwhile get processes and affect the
> > > new iotlb?
> > Isn't the msg processing stopped at the moment this function is called
> > (VHOST_SET_FEATURES)?
> >
> > Thanks
> >
> > Eric
>
> It's pretty late here I'm not sure.  You tell me what prevents it.

So the proposed code assumes that Qemu doesn't process device IOTLB
before VHOST_SET_FEAETURES. Consider there's no reset in the general
vhost uAPI,  I wonder if it's better to move the clear to device code
like VHOST_NET_SET_BACKEND. So we can clear it per vq?

>
> BTW vhost_init_device_iotlb gets enabled parameter but ignores
> it, we really should drop that.

Yes.

>
> Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> and then cleared, iotlb is not properly cleared - bug?

Not sure, old IOTLB may still work. But for safety, we need to disable
device IOTLB in this case.

Thanks

>
>
> > >
> > >
> > >> --
> > >> 2.37.3
>
  

On 11/8/22 04:09, Jason Wang wrote:
> On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>> On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
>>> Hi Michael,
>>> On 11/7/22 21:42, Michael S. Tsirkin wrote:
>>>> On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
>>>>> When the vhost iotlb is used along with a guest virtual iommu
>>>>> and the guest gets rebooted, some MISS messages may have been
>>>>> recorded just before the reboot and spuriously executed by
>>>>> the virtual iommu after the reboot. Despite the device iotlb gets
>>>>> re-initialized, the messages are not cleared. Fix that by calling
>>>>> vhost_clear_msg() at the end of vhost_init_device_iotlb().
>>>>>
>>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>>> ---
>>>>>  drivers/vhost/vhost.c | 1 +
>>>>>  1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>>>> index 40097826cff0..422a1fdee0ca 100644
>>>>> --- a/drivers/vhost/vhost.c
>>>>> +++ b/drivers/vhost/vhost.c
>>>>> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>>>>>    }
>>>>>
>>>>>    vhost_iotlb_free(oiotlb);
>>>>> +  vhost_clear_msg(d);
>>>>>
>>>>>    return 0;
>>>>>  }
>>>> Hmm.  Can't messages meanwhile get processes and affect the
>>>> new iotlb?
>>> Isn't the msg processing stopped at the moment this function is called
>>> (VHOST_SET_FEATURES)?
>>>
>>> Thanks
>>>
>>> Eric
>> It's pretty late here I'm not sure.  You tell me what prevents it.
> So the proposed code assumes that Qemu doesn't process device IOTLB
> before VHOST_SET_FEAETURES. Consider there's no reset in the general
> vhost uAPI,  I wonder if it's better to move the clear to device code
> like VHOST_NET_SET_BACKEND. So we can clear it per vq?

OK I will look at this alternative
>
>> BTW vhost_init_device_iotlb gets enabled parameter but ignores
>> it, we really should drop that.
> Yes.
Yes I saw that too. I will send a patch.
>
>> Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
>> and then cleared, iotlb is not properly cleared - bug?
> Not sure, old IOTLB may still work. But for safety, we need to disable
> device IOTLB in this case.
OK

Thanks

Eric
>
> Thanks
>
>>
>>>>
>>>>> --
>>>>> 2.37.3
  

On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
> On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> > > Hi Michael,
> > > On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > > > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> > > >> When the vhost iotlb is used along with a guest virtual iommu
> > > >> and the guest gets rebooted, some MISS messages may have been
> > > >> recorded just before the reboot and spuriously executed by
> > > >> the virtual iommu after the reboot. Despite the device iotlb gets
> > > >> re-initialized, the messages are not cleared. Fix that by calling
> > > >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> > > >>
> > > >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > >> ---
> > > >>  drivers/vhost/vhost.c | 1 +
> > > >>  1 file changed, 1 insertion(+)
> > > >>
> > > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > >> index 40097826cff0..422a1fdee0ca 100644
> > > >> --- a/drivers/vhost/vhost.c
> > > >> +++ b/drivers/vhost/vhost.c
> > > >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> > > >>    }
> > > >>
> > > >>    vhost_iotlb_free(oiotlb);
> > > >> +  vhost_clear_msg(d);
> > > >>
> > > >>    return 0;
> > > >>  }
> > > > Hmm.  Can't messages meanwhile get processes and affect the
> > > > new iotlb?
> > > Isn't the msg processing stopped at the moment this function is called
> > > (VHOST_SET_FEATURES)?
> > >
> > > Thanks
> > >
> > > Eric
> >
> > It's pretty late here I'm not sure.  You tell me what prevents it.
> 
> So the proposed code assumes that Qemu doesn't process device IOTLB
> before VHOST_SET_FEAETURES. Consider there's no reset in the general
> vhost uAPI,  I wonder if it's better to move the clear to device code
> like VHOST_NET_SET_BACKEND. So we can clear it per vq?

Hmm this makes no sense to me. iommu sits between backend
and frontend. Tying one to another is going to backfire.

I'm thinking more along the lines of doing everything
under iotlb_lock.



> >
> > BTW vhost_init_device_iotlb gets enabled parameter but ignores
> > it, we really should drop that.
> 
> Yes.
> 
> >
> > Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> > and then cleared, iotlb is not properly cleared - bug?
> 
> Not sure, old IOTLB may still work. But for safety, we need to disable
> device IOTLB in this case.
> 
> Thanks
> 
> >
> >
> > > >
> > > >
> > > >> --
> > > >> 2.37.3
> >
  

On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
> > On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > >
> > > On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> > > > Hi Michael,
> > > > On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > > > > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> > > > >> When the vhost iotlb is used along with a guest virtual iommu
> > > > >> and the guest gets rebooted, some MISS messages may have been
> > > > >> recorded just before the reboot and spuriously executed by
> > > > >> the virtual iommu after the reboot. Despite the device iotlb gets
> > > > >> re-initialized, the messages are not cleared. Fix that by calling
> > > > >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> > > > >>
> > > > >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > > >> ---
> > > > >>  drivers/vhost/vhost.c | 1 +
> > > > >>  1 file changed, 1 insertion(+)
> > > > >>
> > > > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > >> index 40097826cff0..422a1fdee0ca 100644
> > > > >> --- a/drivers/vhost/vhost.c
> > > > >> +++ b/drivers/vhost/vhost.c
> > > > >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> > > > >>    }
> > > > >>
> > > > >>    vhost_iotlb_free(oiotlb);
> > > > >> +  vhost_clear_msg(d);
> > > > >>
> > > > >>    return 0;
> > > > >>  }
> > > > > Hmm.  Can't messages meanwhile get processes and affect the
> > > > > new iotlb?
> > > > Isn't the msg processing stopped at the moment this function is called
> > > > (VHOST_SET_FEATURES)?
> > > >
> > > > Thanks
> > > >
> > > > Eric
> > >
> > > It's pretty late here I'm not sure.  You tell me what prevents it.
> >
> > So the proposed code assumes that Qemu doesn't process device IOTLB
> > before VHOST_SET_FEAETURES. Consider there's no reset in the general
> > vhost uAPI,  I wonder if it's better to move the clear to device code
> > like VHOST_NET_SET_BACKEND. So we can clear it per vq?
>
> Hmm this makes no sense to me. iommu sits between backend
> and frontend. Tying one to another is going to backfire.

I think we need to emulate what real devices are doing. Device should
clear the page fault message during reset, so the driver won't read
anything after reset. But we don't have a per device stop or reset
message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
my mind.

>
> I'm thinking more along the lines of doing everything
> under iotlb_lock.

I think the problem is we need to find a proper place to clear the
message. So I don't get how iotlb_lock can help: the message could be
still read from user space after the backend is set to NULL.

Thanks

>
>
>
> > >
> > > BTW vhost_init_device_iotlb gets enabled parameter but ignores
> > > it, we really should drop that.
> >
> > Yes.
> >
> > >
> > > Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> > > and then cleared, iotlb is not properly cleared - bug?
> >
> > Not sure, old IOTLB may still work. But for safety, we need to disable
> > device IOTLB in this case.
> >
> > Thanks
> >
> > >
> > >
> > > > >
> > > > >
> > > > >> --
> > > > >> 2.37.3
> > >
>
  

On Tue, Nov 08, 2022 at 05:13:50PM +0800, Jason Wang wrote:
> On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >
> > On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
> > > On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > >
> > > > On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> > > > > Hi Michael,
> > > > > On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > > > > > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> > > > > >> When the vhost iotlb is used along with a guest virtual iommu
> > > > > >> and the guest gets rebooted, some MISS messages may have been
> > > > > >> recorded just before the reboot and spuriously executed by
> > > > > >> the virtual iommu after the reboot. Despite the device iotlb gets
> > > > > >> re-initialized, the messages are not cleared. Fix that by calling
> > > > > >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> > > > > >>
> > > > > >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > > > >> ---
> > > > > >>  drivers/vhost/vhost.c | 1 +
> > > > > >>  1 file changed, 1 insertion(+)
> > > > > >>
> > > > > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > > >> index 40097826cff0..422a1fdee0ca 100644
> > > > > >> --- a/drivers/vhost/vhost.c
> > > > > >> +++ b/drivers/vhost/vhost.c
> > > > > >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> > > > > >>    }
> > > > > >>
> > > > > >>    vhost_iotlb_free(oiotlb);
> > > > > >> +  vhost_clear_msg(d);
> > > > > >>
> > > > > >>    return 0;
> > > > > >>  }
> > > > > > Hmm.  Can't messages meanwhile get processes and affect the
> > > > > > new iotlb?
> > > > > Isn't the msg processing stopped at the moment this function is called
> > > > > (VHOST_SET_FEATURES)?
> > > > >
> > > > > Thanks
> > > > >
> > > > > Eric
> > > >
> > > > It's pretty late here I'm not sure.  You tell me what prevents it.
> > >
> > > So the proposed code assumes that Qemu doesn't process device IOTLB
> > > before VHOST_SET_FEAETURES. Consider there's no reset in the general
> > > vhost uAPI,  I wonder if it's better to move the clear to device code
> > > like VHOST_NET_SET_BACKEND. So we can clear it per vq?
> >
> > Hmm this makes no sense to me. iommu sits between backend
> > and frontend. Tying one to another is going to backfire.
> 
> I think we need to emulate what real devices are doing. Device should
> clear the page fault message during reset, so the driver won't read
> anything after reset. But we don't have a per device stop or reset
> message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
> my mind.

That's not a reset message. Userspace can switch backends at will.
I guess we could check when backend is set to -1.
It's a hack but might work.

> >
> > I'm thinking more along the lines of doing everything
> > under iotlb_lock.
> 
> I think the problem is we need to find a proper place to clear the
> message. So I don't get how iotlb_lock can help: the message could be
> still read from user space after the backend is set to NULL.
> 
> Thanks

Well I think the real problem is this.

vhost_net_set_features does:

        if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
                if (vhost_init_device_iotlb(&n->dev, true))
                        goto out_unlock;
        }


so we get a new iotlb each time features are set.

But features can be changes while device is running.
E.g.
	VHOST_F_LOG_ALL


Let's just say this hack of reusing feature bits for backend
was not my brightest idea :(





> >
> >
> >
> > > >
> > > > BTW vhost_init_device_iotlb gets enabled parameter but ignores
> > > > it, we really should drop that.
> > >
> > > Yes.
> > >
> > > >
> > > > Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> > > > and then cleared, iotlb is not properly cleared - bug?
> > >
> > > Not sure, old IOTLB may still work. But for safety, we need to disable
> > > device IOTLB in this case.
> > >
> > > Thanks
> > >
> > > >
> > > >
> > > > > >
> > > > > >
> > > > > >> --
> > > > > >> 2.37.3
> > > >
> >
  

Hi Michael, Jason,

On 11/8/22 10:31, Michael S. Tsirkin wrote:
> On Tue, Nov 08, 2022 at 05:13:50PM +0800, Jason Wang wrote:
>> On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>>> On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
>>>> On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>> On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
>>>>>> Hi Michael,
>>>>>> On 11/7/22 21:42, Michael S. Tsirkin wrote:
>>>>>>> On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
>>>>>>>> When the vhost iotlb is used along with a guest virtual iommu
>>>>>>>> and the guest gets rebooted, some MISS messages may have been
>>>>>>>> recorded just before the reboot and spuriously executed by
>>>>>>>> the virtual iommu after the reboot. Despite the device iotlb gets
>>>>>>>> re-initialized, the messages are not cleared. Fix that by calling
>>>>>>>> vhost_clear_msg() at the end of vhost_init_device_iotlb().
>>>>>>>>
>>>>>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>>>>>> ---
>>>>>>>>  drivers/vhost/vhost.c | 1 +
>>>>>>>>  1 file changed, 1 insertion(+)
>>>>>>>>
>>>>>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>>>>>>> index 40097826cff0..422a1fdee0ca 100644
>>>>>>>> --- a/drivers/vhost/vhost.c
>>>>>>>> +++ b/drivers/vhost/vhost.c
>>>>>>>> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>>>>>>>>    }
>>>>>>>>
>>>>>>>>    vhost_iotlb_free(oiotlb);
>>>>>>>> +  vhost_clear_msg(d);
>>>>>>>>
>>>>>>>>    return 0;
>>>>>>>>  }
>>>>>>> Hmm.  Can't messages meanwhile get processes and affect the
>>>>>>> new iotlb?
>>>>>> Isn't the msg processing stopped at the moment this function is called
>>>>>> (VHOST_SET_FEATURES)?
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>> Eric
>>>>> It's pretty late here I'm not sure.  You tell me what prevents it.
>>>> So the proposed code assumes that Qemu doesn't process device IOTLB
>>>> before VHOST_SET_FEAETURES. Consider there's no reset in the general
>>>> vhost uAPI,  I wonder if it's better to move the clear to device code
>>>> like VHOST_NET_SET_BACKEND. So we can clear it per vq?
>>> Hmm this makes no sense to me. iommu sits between backend
>>> and frontend. Tying one to another is going to backfire.
>> I think we need to emulate what real devices are doing. Device should
>> clear the page fault message during reset, so the driver won't read
>> anything after reset. But we don't have a per device stop or reset
>> message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
>> my mind.
> That's not a reset message. Userspace can switch backends at will.
> I guess we could check when backend is set to -1.
> It's a hack but might work.
>
>>> I'm thinking more along the lines of doing everything
>>> under iotlb_lock.
>> I think the problem is we need to find a proper place to clear the
>> message. So I don't get how iotlb_lock can help: the message could be
>> still read from user space after the backend is set to NULL.
>>
>> Thanks
> Well I think the real problem is this.
>
> vhost_net_set_features does:
>
>         if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
>                 if (vhost_init_device_iotlb(&n->dev, true))
>                         goto out_unlock;
>         }
>
>
> so we get a new iotlb each time features are set.
>
> But features can be changes while device is running.
> E.g.
> 	VHOST_F_LOG_ALL
>
>
> Let's just say this hack of reusing feature bits for backend
> was not my brightest idea :(
>

Isn't vhost_init_device_iotlb() racy then, as d->iotlb is first updated with niotlb and later d->vqs[i]->iotlb is updated with niotlb. What does garantee this is done atomically?

Shouldn't we hold the dev->mutex to make all the sequence atomic and
include vhost_clear_msg()?  Can't the vhost_clear_msg() take the dev lock?

Thanks

Eric

>
>
>
>>>
>>>
>>>>> BTW vhost_init_device_iotlb gets enabled parameter but ignores
>>>>> it, we really should drop that.
>>>> Yes.
>>>>
>>>>> Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
>>>>> and then cleared, iotlb is not properly cleared - bug?
>>>> Not sure, old IOTLB may still work. But for safety, we need to disable
>>>> device IOTLB in this case.
>>>>
>>>> Thanks
>>>>
>>>>>
>>>>>>>
>>>>>>>> --
>>>>>>>> 2.37.3
  

On Tue, Nov 8, 2022 at 5:31 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>
> On Tue, Nov 08, 2022 at 05:13:50PM +0800, Jason Wang wrote:
> > On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> > >
> > > On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
> > > > On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> > > > >
> > > > > On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> > > > > > Hi Michael,
> > > > > > On 11/7/22 21:42, Michael S. Tsirkin wrote:
> > > > > > > On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> > > > > > >> When the vhost iotlb is used along with a guest virtual iommu
> > > > > > >> and the guest gets rebooted, some MISS messages may have been
> > > > > > >> recorded just before the reboot and spuriously executed by
> > > > > > >> the virtual iommu after the reboot. Despite the device iotlb gets
> > > > > > >> re-initialized, the messages are not cleared. Fix that by calling
> > > > > > >> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> > > > > > >>
> > > > > > >> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> > > > > > >> ---
> > > > > > >>  drivers/vhost/vhost.c | 1 +
> > > > > > >>  1 file changed, 1 insertion(+)
> > > > > > >>
> > > > > > >> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> > > > > > >> index 40097826cff0..422a1fdee0ca 100644
> > > > > > >> --- a/drivers/vhost/vhost.c
> > > > > > >> +++ b/drivers/vhost/vhost.c
> > > > > > >> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> > > > > > >>    }
> > > > > > >>
> > > > > > >>    vhost_iotlb_free(oiotlb);
> > > > > > >> +  vhost_clear_msg(d);
> > > > > > >>
> > > > > > >>    return 0;
> > > > > > >>  }
> > > > > > > Hmm.  Can't messages meanwhile get processes and affect the
> > > > > > > new iotlb?
> > > > > > Isn't the msg processing stopped at the moment this function is called
> > > > > > (VHOST_SET_FEATURES)?
> > > > > >
> > > > > > Thanks
> > > > > >
> > > > > > Eric
> > > > >
> > > > > It's pretty late here I'm not sure.  You tell me what prevents it.
> > > >
> > > > So the proposed code assumes that Qemu doesn't process device IOTLB
> > > > before VHOST_SET_FEAETURES. Consider there's no reset in the general
> > > > vhost uAPI,  I wonder if it's better to move the clear to device code
> > > > like VHOST_NET_SET_BACKEND. So we can clear it per vq?
> > >
> > > Hmm this makes no sense to me. iommu sits between backend
> > > and frontend. Tying one to another is going to backfire.
> >
> > I think we need to emulate what real devices are doing. Device should
> > clear the page fault message during reset, so the driver won't read
> > anything after reset. But we don't have a per device stop or reset
> > message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
> > my mind.
>
> That's not a reset message. Userspace can switch backends at will.
> I guess we could check when backend is set to -1.
> It's a hack but might work.

Yes, that's what I meant actually.

>
> > >
> > > I'm thinking more along the lines of doing everything
> > > under iotlb_lock.
> >
> > I think the problem is we need to find a proper place to clear the
> > message. So I don't get how iotlb_lock can help: the message could be
> > still read from user space after the backend is set to NULL.
> >
> > Thanks
>
> Well I think the real problem is this.
>
> vhost_net_set_features does:
>
>         if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
>                 if (vhost_init_device_iotlb(&n->dev, true))
>                         goto out_unlock;
>         }
>
>
> so we get a new iotlb each time features are set.

Right, but this looks like another independent issue that needs to be fixed.

>
> But features can be changes while device is running.
> E.g.
>         VHOST_F_LOG_ALL
>
>
> Let's just say this hack of reusing feature bits for backend
> was not my brightest idea :(
>

Probably :)

Thanks

>
>
>
>
> > >
> > >
> > >
> > > > >
> > > > > BTW vhost_init_device_iotlb gets enabled parameter but ignores
> > > > > it, we really should drop that.
> > > >
> > > > Yes.
> > > >
> > > > >
> > > > > Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> > > > > and then cleared, iotlb is not properly cleared - bug?
> > > >
> > > > Not sure, old IOTLB may still work. But for safety, we need to disable
> > > > device IOTLB in this case.
> > > >
> > > > Thanks
> > > >
> > > > >
> > > > >
> > > > > > >
> > > > > > >
> > > > > > >> --
> > > > > > >> 2.37.3
> > > > >
> > >
>
  

On Tue, Nov 8, 2022 at 6:17 PM Eric Auger <eric.auger@redhat.com> wrote:
>
> Hi Michael, Jason,
>
> On 11/8/22 10:31, Michael S. Tsirkin wrote:
> > On Tue, Nov 08, 2022 at 05:13:50PM +0800, Jason Wang wrote:
> >> On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
> >>> On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
> >>>> On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
> >>>>> On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
> >>>>>> Hi Michael,
> >>>>>> On 11/7/22 21:42, Michael S. Tsirkin wrote:
> >>>>>>> On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
> >>>>>>>> When the vhost iotlb is used along with a guest virtual iommu
> >>>>>>>> and the guest gets rebooted, some MISS messages may have been
> >>>>>>>> recorded just before the reboot and spuriously executed by
> >>>>>>>> the virtual iommu after the reboot. Despite the device iotlb gets
> >>>>>>>> re-initialized, the messages are not cleared. Fix that by calling
> >>>>>>>> vhost_clear_msg() at the end of vhost_init_device_iotlb().
> >>>>>>>>
> >>>>>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
> >>>>>>>> ---
> >>>>>>>>  drivers/vhost/vhost.c | 1 +
> >>>>>>>>  1 file changed, 1 insertion(+)
> >>>>>>>>
> >>>>>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
> >>>>>>>> index 40097826cff0..422a1fdee0ca 100644
> >>>>>>>> --- a/drivers/vhost/vhost.c
> >>>>>>>> +++ b/drivers/vhost/vhost.c
> >>>>>>>> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
> >>>>>>>>    }
> >>>>>>>>
> >>>>>>>>    vhost_iotlb_free(oiotlb);
> >>>>>>>> +  vhost_clear_msg(d);
> >>>>>>>>
> >>>>>>>>    return 0;
> >>>>>>>>  }
> >>>>>>> Hmm.  Can't messages meanwhile get processes and affect the
> >>>>>>> new iotlb?
> >>>>>> Isn't the msg processing stopped at the moment this function is called
> >>>>>> (VHOST_SET_FEATURES)?
> >>>>>>
> >>>>>> Thanks
> >>>>>>
> >>>>>> Eric
> >>>>> It's pretty late here I'm not sure.  You tell me what prevents it.
> >>>> So the proposed code assumes that Qemu doesn't process device IOTLB
> >>>> before VHOST_SET_FEAETURES. Consider there's no reset in the general
> >>>> vhost uAPI,  I wonder if it's better to move the clear to device code
> >>>> like VHOST_NET_SET_BACKEND. So we can clear it per vq?
> >>> Hmm this makes no sense to me. iommu sits between backend
> >>> and frontend. Tying one to another is going to backfire.
> >> I think we need to emulate what real devices are doing. Device should
> >> clear the page fault message during reset, so the driver won't read
> >> anything after reset. But we don't have a per device stop or reset
> >> message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
> >> my mind.
> > That's not a reset message. Userspace can switch backends at will.
> > I guess we could check when backend is set to -1.
> > It's a hack but might work.
> >
> >>> I'm thinking more along the lines of doing everything
> >>> under iotlb_lock.
> >> I think the problem is we need to find a proper place to clear the
> >> message. So I don't get how iotlb_lock can help: the message could be
> >> still read from user space after the backend is set to NULL.
> >>
> >> Thanks
> > Well I think the real problem is this.
> >
> > vhost_net_set_features does:
> >
> >         if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
> >                 if (vhost_init_device_iotlb(&n->dev, true))
> >                         goto out_unlock;
> >         }
> >
> >
> > so we get a new iotlb each time features are set.
> >
> > But features can be changes while device is running.
> > E.g.
> >       VHOST_F_LOG_ALL
> >
> >
> > Let's just say this hack of reusing feature bits for backend
> > was not my brightest idea :(
> >
>
> Isn't vhost_init_device_iotlb() racy then, as d->iotlb is first updated with niotlb and later d->vqs[i]->iotlb is updated with niotlb. What does garantee this is done atomically?
>
> Shouldn't we hold the dev->mutex to make all the sequence atomic and
> include vhost_clear_msg()?  Can't the vhost_clear_msg() take the dev lock?

It depends on where we want to place the vhost_clear_msg(), e.g in
most of the device ioctl, the dev->mutex has been held.

Thanks

>
> Thanks
>
> Eric
>
> >
> >
> >
> >>>
> >>>
> >>>>> BTW vhost_init_device_iotlb gets enabled parameter but ignores
> >>>>> it, we really should drop that.
> >>>> Yes.
> >>>>
> >>>>> Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
> >>>>> and then cleared, iotlb is not properly cleared - bug?
> >>>> Not sure, old IOTLB may still work. But for safety, we need to disable
> >>>> device IOTLB in this case.
> >>>>
> >>>> Thanks
> >>>>
> >>>>>
> >>>>>>>
> >>>>>>>> --
> >>>>>>>> 2.37.3
>
  

Hi Jason,

On 11/9/22 04:44, Jason Wang wrote:
> On Tue, Nov 8, 2022 at 6:17 PM Eric Auger <eric.auger@redhat.com> wrote:
>> Hi Michael, Jason,
>>
>> On 11/8/22 10:31, Michael S. Tsirkin wrote:
>>> On Tue, Nov 08, 2022 at 05:13:50PM +0800, Jason Wang wrote:
>>>> On Tue, Nov 8, 2022 at 4:56 PM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>> On Tue, Nov 08, 2022 at 11:09:36AM +0800, Jason Wang wrote:
>>>>>> On Tue, Nov 8, 2022 at 7:06 AM Michael S. Tsirkin <mst@redhat.com> wrote:
>>>>>>> On Mon, Nov 07, 2022 at 10:10:06PM +0100, Eric Auger wrote:
>>>>>>>> Hi Michael,
>>>>>>>> On 11/7/22 21:42, Michael S. Tsirkin wrote:
>>>>>>>>> On Mon, Nov 07, 2022 at 09:34:31PM +0100, Eric Auger wrote:
>>>>>>>>>> When the vhost iotlb is used along with a guest virtual iommu
>>>>>>>>>> and the guest gets rebooted, some MISS messages may have been
>>>>>>>>>> recorded just before the reboot and spuriously executed by
>>>>>>>>>> the virtual iommu after the reboot. Despite the device iotlb gets
>>>>>>>>>> re-initialized, the messages are not cleared. Fix that by calling
>>>>>>>>>> vhost_clear_msg() at the end of vhost_init_device_iotlb().
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Eric Auger <eric.auger@redhat.com>
>>>>>>>>>> ---
>>>>>>>>>>  drivers/vhost/vhost.c | 1 +
>>>>>>>>>>  1 file changed, 1 insertion(+)
>>>>>>>>>>
>>>>>>>>>> diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
>>>>>>>>>> index 40097826cff0..422a1fdee0ca 100644
>>>>>>>>>> --- a/drivers/vhost/vhost.c
>>>>>>>>>> +++ b/drivers/vhost/vhost.c
>>>>>>>>>> @@ -1751,6 +1751,7 @@ int vhost_init_device_iotlb(struct vhost_dev *d, bool enabled)
>>>>>>>>>>    }
>>>>>>>>>>
>>>>>>>>>>    vhost_iotlb_free(oiotlb);
>>>>>>>>>> +  vhost_clear_msg(d);
>>>>>>>>>>
>>>>>>>>>>    return 0;
>>>>>>>>>>  }
>>>>>>>>> Hmm.  Can't messages meanwhile get processes and affect the
>>>>>>>>> new iotlb?
>>>>>>>> Isn't the msg processing stopped at the moment this function is called
>>>>>>>> (VHOST_SET_FEATURES)?
>>>>>>>>
>>>>>>>> Thanks
>>>>>>>>
>>>>>>>> Eric
>>>>>>> It's pretty late here I'm not sure.  You tell me what prevents it.
>>>>>> So the proposed code assumes that Qemu doesn't process device IOTLB
>>>>>> before VHOST_SET_FEAETURES. Consider there's no reset in the general
>>>>>> vhost uAPI,  I wonder if it's better to move the clear to device code
>>>>>> like VHOST_NET_SET_BACKEND. So we can clear it per vq?
>>>>> Hmm this makes no sense to me. iommu sits between backend
>>>>> and frontend. Tying one to another is going to backfire.
>>>> I think we need to emulate what real devices are doing. Device should
>>>> clear the page fault message during reset, so the driver won't read
>>>> anything after reset. But we don't have a per device stop or reset
>>>> message for vhost-net. That's why the VHOST_NET_SET_BACKEND came into
>>>> my mind.
>>> That's not a reset message. Userspace can switch backends at will.
>>> I guess we could check when backend is set to -1.
>>> It's a hack but might work.
>>>
>>>>> I'm thinking more along the lines of doing everything
>>>>> under iotlb_lock.
>>>> I think the problem is we need to find a proper place to clear the
>>>> message. So I don't get how iotlb_lock can help: the message could be
>>>> still read from user space after the backend is set to NULL.
>>>>
>>>> Thanks
>>> Well I think the real problem is this.
>>>
>>> vhost_net_set_features does:
>>>
>>>         if ((features & (1ULL << VIRTIO_F_ACCESS_PLATFORM))) {
>>>                 if (vhost_init_device_iotlb(&n->dev, true))
>>>                         goto out_unlock;
>>>         }
>>>
>>>
>>> so we get a new iotlb each time features are set.
>>>
>>> But features can be changes while device is running.
>>> E.g.
>>>       VHOST_F_LOG_ALL
>>>
>>>
>>> Let's just say this hack of reusing feature bits for backend
>>> was not my brightest idea :(
>>>
>> Isn't vhost_init_device_iotlb() racy then, as d->iotlb is first updated with niotlb and later d->vqs[i]->iotlb is updated with niotlb. What does garantee this is done atomically?
>>
>> Shouldn't we hold the dev->mutex to make all the sequence atomic and
>> include vhost_clear_msg()?  Can't the vhost_clear_msg() take the dev lock?
> It depends on where we want to place the vhost_clear_msg(), e.g in
> most of the device ioctl, the dev->mutex has been held.

OK, I will double check and respin accordingly

Eric
>
> Thanks
>
>> Thanks
>>
>> Eric
>>
>>>
>>>
>>>>>
>>>>>>> BTW vhost_init_device_iotlb gets enabled parameter but ignores
>>>>>>> it, we really should drop that.
>>>>>> Yes.
>>>>>>
>>>>>>> Also, it looks like if features are set with VIRTIO_F_ACCESS_PLATFORM
>>>>>>> and then cleared, iotlb is not properly cleared - bug?
>>>>>> Not sure, old IOTLB may still work. But for safety, we need to disable
>>>>>> device IOTLB in this case.
>>>>>>
>>>>>> Thanks
>>>>>>
>>>>>>>>>> --
>>>>>>>>>> 2.37.3