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Subject: Re: [PATCH v3 1/1] s390: virtio: let arch accept devices without
 IOMMU feature
To:     Tom Lendacky <thomas.lendacky@amd.com>,
        linux-kernel@vger.kernel.org
Cc:     pasic@linux.ibm.com, borntraeger@de.ibm.com, frankja@linux.ibm.com,
        mst@redhat.com, jasowang@redhat.com, cohuck@redhat.com,
        kvm@vger.kernel.org, linux-s390@vger.kernel.org,
        virtualization@lists.linux-foundation.org,
        david@gibson.dropbear.id.au, linuxram@us.ibm.com,
        heiko.carstens@de.ibm.com, gor@linux.ibm.com
References: <1592390637-17441-1-git-send-email-pmorel@linux.ibm.com>
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 <e5204218-6e93-8713-6056-2a62531c310e@amd.com>
From:   Pierre Morel <pmorel@linux.ibm.com>
Message-ID: <64544f14-eecf-6dda-d232-0bceeb2840ff@linux.ibm.com>
Date:   Wed, 17 Jun 2020 16:12:42 +0200
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On 2020-06-17 15:36, Tom Lendacky wrote:
> On 6/17/20 5:43 AM, Pierre Morel wrote:
>> An architecture protecting the guest memory against unauthorized host
>> access may want to enforce VIRTIO I/O device protection through the
>> use of VIRTIO_F_IOMMU_PLATFORM.
>>
>> Let's give a chance to the architecture to accept or not devices
>> without VIRTIO_F_IOMMU_PLATFORM.
>>
>> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
>> Acked-by: Jason Wang <jasowang@redhat.com>
>> Acked-by: Christian Borntraeger <borntraeger@de.ibm.com>
>> ---
>>   arch/s390/mm/init.c     |  6 ++++++
>>   drivers/virtio/virtio.c | 22 ++++++++++++++++++++++
>>   include/linux/virtio.h  |  2 ++
>>   3 files changed, 30 insertions(+)
>>
>> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
>> index 6dc7c3b60ef6..215070c03226 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.h>
>>   
>>   pgd_t swapper_pg_dir[PTRS_PER_PGD] __section(.bss..swapper_pg_dir);
>>   
>> @@ -161,6 +162,11 @@ bool force_dma_unencrypted(struct device *dev)
>>   	return is_prot_virt_guest();
>>   }
>>   
>> +int arch_needs_virtio_iommu_platform(struct virtio_device *dev)
>> +{
>> +	return is_prot_virt_guest();
>> +}
>> +
>>   /* protected virtualization */
>>   static void pv_init(void)
>>   {
>> diff --git a/drivers/virtio/virtio.c b/drivers/virtio/virtio.c
>> index a977e32a88f2..aa8e01104f86 100644
>> --- a/drivers/virtio/virtio.c
>> +++ b/drivers/virtio/virtio.c
>> @@ -167,6 +167,21 @@ void virtio_add_status(struct virtio_device *dev, unsigned int status)
>>   }
>>   EXPORT_SYMBOL_GPL(virtio_add_status);
>>   
>> +/*
>> + * arch_needs_virtio_iommu_platform - provide arch specific hook when finalizing
>> + *				      features for VIRTIO device dev
>> + * @dev: the VIRTIO device being added
>> + *
>> + * Permits the platform to provide architecture specific functionality when
>> + * devices features are finalized. This is the default implementation.
>> + * Architecture implementations can override this.
>> + */
>> +
>> +int __weak arch_needs_virtio_iommu_platform(struct virtio_device *dev)
>> +{
>> +	return 0;
>> +}
>> +
>>   int virtio_finalize_features(struct virtio_device *dev)
>>   {
>>   	int ret = dev->config->finalize_features(dev);
>> @@ -179,6 +194,13 @@ int virtio_finalize_features(struct virtio_device *dev)
>>   	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1))
>>   		return 0;
>>   
>> +	if (arch_needs_virtio_iommu_platform(dev) &&
>> +		!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> 
> Just a style nit, but the "!virtio..." should be directly under the
> "arch_...", not tabbed out.

Oh right, thanks!

Pierre

> 
> Thanks,
> Tom
> 

...snip...

-- 
Pierre Morel
IBM Lab Boeblingen