Linux Virtualization - Jul 2020 - [PATCH v7 2/2] s390: virtio: PV needs VIRTIO I/O device protection

On Wed, Jul 15, 2020 at 10:31:09AM +0200, Pierre Morel
wrote:
> If protected virtualization is active on s390, the virtio queues are
> not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
> negotiated. Use the new arch_validate_virtio_features() interface to
> fail probe if that's not the case, preventing a host error on access
> attempt.
> 
> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
> Reviewed-by: Cornelia Huck <cohuck at redhat.com>
> Acked-by: Halil Pasic <pasic at linux.ibm.com>
> Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
> ---
>  arch/s390/mm/init.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
> 
> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> index 6dc7c3b60ef6..d39af6554d4f 100644
> --- a/arch/s390/mm/init.c
> +++ b/arch/s390/mm/init.c
> @@ -45,6 +45,7 @@
>  #include <asm/kasan.h>
>  #include <asm/dma-mapping.h>
>  #include <asm/uv.h>
> +#include <linux/virtio_config.h>
>  
>  pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>  
> @@ -161,6 +162,33 @@ bool force_dma_unencrypted(struct device *dev)
>  	return is_prot_virt_guest();
>  }
>  
> +/*
> + * arch_validate_virtio_features
> + * @dev: the VIRTIO device being added
> + *
> + * Return an error if required features are missing on a guest running
> + * with protected virtualization.
> + */
> +int arch_validate_virtio_features(struct virtio_device *dev)
> +{
> +	if (!is_prot_virt_guest())
> +		return 0;
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +		dev_warn(&dev->dev,
> +			 "legacy virtio not supported with protected
virtualization\n");
> +		return -ENODEV;
> +	}
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> +		dev_warn(&dev->dev,
> +			 "support for limited memory access required for protected
virtualization\n");
> +		return -ENODEV;
> +	}
> +
> +	return 0;
> +}
> +
>  /* protected virtualization */
>  static void pv_init(void)
>  {
What bothers me here is that arch code depends on virtio now.
It works even with a modular virtio when functions are inline,
but it seems fragile: e.g. it breaks virtio as an out of tree module,
since layout of struct virtio_device can change.

I'm not sure what to do with this yet, will try to think about it
over the weekend. Thanks!

> -- 
> 2.25.1

On 2020/7/15 ??5:50, Michael S. Tsirkin wrote:
> On Wed, Jul 15, 2020 at 10:31:09AM +0200, Pierre Morel wrote:
>> If protected virtualization is active on s390, the virtio queues are
>> not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has been
>> negotiated. Use the new arch_validate_virtio_features() interface to
>> fail probe if that's not the case, preventing a host error on
access
>> attempt.
>>
>> Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
>> Reviewed-by: Cornelia Huck <cohuck at redhat.com>
>> Acked-by: Halil Pasic <pasic at linux.ibm.com>
>> Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
>> ---
>>   arch/s390/mm/init.c | 28 ++++++++++++++++++++++++++++
>>   1 file changed, 28 insertions(+)
>>
>> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
>> index 6dc7c3b60ef6..d39af6554d4f 100644
>> --- a/arch/s390/mm/init.c
>> +++ b/arch/s390/mm/init.c
>> @@ -45,6 +45,7 @@
>>   #include <asm/kasan.h>
>>   #include <asm/dma-mapping.h>
>>   #include <asm/uv.h>
>> +#include <linux/virtio_config.h>
>>   
>>   pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>>   
>> @@ -161,6 +162,33 @@ bool force_dma_unencrypted(struct device *dev)
>>   	return is_prot_virt_guest();
>>   }
>>   
>> +/*
>> + * arch_validate_virtio_features
>> + * @dev: the VIRTIO device being added
>> + *
>> + * Return an error if required features are missing on a guest running
>> + * with protected virtualization.
>> + */
>> +int arch_validate_virtio_features(struct virtio_device *dev)
>> +{
>> +	if (!is_prot_virt_guest())
>> +		return 0;
>> +
>> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
>> +		dev_warn(&dev->dev,
>> +			 "legacy virtio not supported with protected
virtualization\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
>> +		dev_warn(&dev->dev,
>> +			 "support for limited memory access required for protected
virtualization\n");
>> +		return -ENODEV;
>> +	}
>> +
>> +	return 0;
>> +}
>> +
>>   /* protected virtualization */
>>   static void pv_init(void)
>>   {
> What bothers me here is that arch code depends on virtio now.
> It works even with a modular virtio when functions are inline,
> but it seems fragile: e.g. it breaks virtio as an out of tree module,
> since layout of struct virtio_device can change.

The code was only called from virtio.c so it should be fine.

And my understanding is that we don't need to care about the kABI issue 
during upstream development?

Thanks

>
> I'm not sure what to do with this yet, will try to think about it
> over the weekend. Thanks!
>
>
>> -- 
>> 2.25.1

On Wed, Jul 15, 2020 at 06:16:59PM +0800, Jason Wang
wrote:
> 
> On 2020/7/15 ??5:50, Michael S. Tsirkin wrote:
> > On Wed, Jul 15, 2020 at 10:31:09AM +0200, Pierre Morel wrote:
> > > If protected virtualization is active on s390, the virtio queues
are
> > > not accessible to the host, unless VIRTIO_F_IOMMU_PLATFORM has
been
> > > negotiated. Use the new arch_validate_virtio_features() interface
to
> > > fail probe if that's not the case, preventing a host error on
access
> > > attempt.
> > > 
> > > Signed-off-by: Pierre Morel <pmorel at linux.ibm.com>
> > > Reviewed-by: Cornelia Huck <cohuck at redhat.com>
> > > Acked-by: Halil Pasic <pasic at linux.ibm.com>
> > > Acked-by: Christian Borntraeger <borntraeger at de.ibm.com>
> > > ---
> > >   arch/s390/mm/init.c | 28 ++++++++++++++++++++++++++++
> > >   1 file changed, 28 insertions(+)
> > > 
> > > diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
> > > index 6dc7c3b60ef6..d39af6554d4f 100644
> > > --- a/arch/s390/mm/init.c
> > > +++ b/arch/s390/mm/init.c
> > > @@ -45,6 +45,7 @@
> > >   #include <asm/kasan.h>
> > >   #include <asm/dma-mapping.h>
> > >   #include <asm/uv.h>
> > > +#include <linux/virtio_config.h>
> > >   pgd_t swapper_pg_dir[PTRS_PER_PGD]
__section(.bss..swapper_pg_dir);
> > > @@ -161,6 +162,33 @@ bool force_dma_unencrypted(struct device
*dev)
> > >   	return is_prot_virt_guest();
> > >   }
> > > +/*
> > > + * arch_validate_virtio_features
> > > + * @dev: the VIRTIO device being added
> > > + *
> > > + * Return an error if required features are missing on a guest
running
> > > + * with protected virtualization.
> > > + */
> > > +int arch_validate_virtio_features(struct virtio_device *dev)
> > > +{
> > > +	if (!is_prot_virt_guest())
> > > +		return 0;
> > > +
> > > +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> > > +		dev_warn(&dev->dev,
> > > +			 "legacy virtio not supported with protected
virtualization\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> > > +		dev_warn(&dev->dev,
> > > +			 "support for limited memory access required for
protected virtualization\n");
> > > +		return -ENODEV;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > >   /* protected virtualization */
> > >   static void pv_init(void)
> > >   {
> > What bothers me here is that arch code depends on virtio now.
> > It works even with a modular virtio when functions are inline,
> > but it seems fragile: e.g. it breaks virtio as an out of tree module,
> > since layout of struct virtio_device can change.
> 
> 
> The code was only called from virtio.c so it should be fine.
> 
> And my understanding is that we don't need to care about the kABI issue
> during upstream development?
> 
> Thanks
No, but so far it has been convenient at least for me, for development,
to just be able to unload all of virtio and load a different version.

> 
> > 
> > I'm not sure what to do with this yet, will try to think about it
> > over the weekend. Thanks!
> > 
> > 
> > > -- 
> > > 2.25.1