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Subject: Re: [PATCH v4 2/2] s390: virtio: PV needs VIRTIO I/O device
 protection
To:     Pierre Morel <pmorel@linux.ibm.com>, linux-kernel@vger.kernel.org
Cc:     pasic@linux.ibm.com, frankja@linux.ibm.com, mst@redhat.com,
        jasowang@redhat.com, cohuck@redhat.com, kvm@vger.kernel.org,
        linux-s390@vger.kernel.org,
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        david@gibson.dropbear.id.au, linuxram@us.ibm.com,
        heiko.carstens@de.ibm.com, gor@linux.ibm.com
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Date:   Tue, 7 Jul 2020 13:12:28 +0200
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On 07.07.20 10:44, Pierre Morel wrote:
> S390, protecting the guest memory against unauthorized host access
> needs to enforce VIRTIO I/O device protection through the use of
> VIRTIO_F_VERSION_1 and VIRTIO_F_IOMMU_PLATFORM.
> 
> Signed-off-by: Pierre Morel <pmorel@linux.ibm.com>
> ---
>  arch/s390/kernel/uv.c | 25 +++++++++++++++++++++++++
>  1 file changed, 25 insertions(+)
> 
> diff --git a/arch/s390/kernel/uv.c b/arch/s390/kernel/uv.c
> index c296e5c8dbf9..106330f6eda1 100644
> --- a/arch/s390/kernel/uv.c
> +++ b/arch/s390/kernel/uv.c
> @@ -14,6 +14,7 @@
>  #include <linux/memblock.h>
>  #include <linux/pagemap.h>
>  #include <linux/swap.h>
> +#include <linux/virtio_config.h>
>  #include <asm/facility.h>
>  #include <asm/sections.h>
>  #include <asm/uv.h>
> @@ -413,3 +414,27 @@ static int __init uv_info_init(void)
>  }
>  device_initcall(uv_info_init);
>  #endif
> +
> +/*
> + * arch_validate_virtio_iommu_platform
> + * @dev: the VIRTIO device being added
> + *
> + * Return value: returns -ENODEV if any features of the
> + *               device breaks the protected virtualization
> + *               0 otherwise.
> + */
> +int arch_validate_virtio_features(struct virtio_device *dev)
> +{
> +	if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> +		dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");

I think you only want to warn if is_prot_virt_guest is true? We certainly
want to be able to run as a guest of older hypervisors with virtio 0.95, no?


> +		return is_prot_virt_guest() ? -ENODEV : 0;
> +	}
> +
> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> +		dev_warn(&dev->dev,
> +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");

same here. 
> +		return is_prot_virt_guest() ? -ENODEV : 0;
> +	}
> +
> +	return 0;
> +}
>