Re: [PATCH v4 2/2] s390: virtio: PV needs VIRTIO I/O device protection

Pierre Morel
2020-07-07T10:39:50Z

On 2020-07-07 11:46, Cornelia Huck wrote:
> On Tue, 7 Jul 2020 10:44:37 +0200
> Pierre Morel <pmorel@linux.ibm.com> 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.
>
> Hm... what about:
>
> "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
> enforce this."

Yes, thanks.

>
>>
>> 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
>
> s/arch_validate_virtio_iommu_platform/arch_validate_virtio_features/
>
>> + * @dev: the VIRTIO device being added
>> + *
>> + * Return value: returns -ENODEV if any features of the
>> + * device breaks the protected virtualization
>> + * 0 otherwise.
>
> I don't think you need to specify the contract here: that belongs to
> the definition in the virtio core. What about simply adding a sentence
> "Return an error if required features are missing on a guest running
> with protected virtualization." ?

OK, right.

>
>> + */
>> +int arch_validate_virtio_features(struct virtio_device *dev)
>> +{
>
> Maybe jump out immediately if the guest is not protected?
>
>> + if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
>> + dev_warn(&dev->dev, "device must provide VIRTIO_F_VERSION_1\n");
>> + 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");
>> + return is_prot_virt_guest() ? -ENODEV : 0;
>> + }
>
> if (!is_prot_virt_guest())
> return 0;
>
> if (!virtio_has_feature(dev, VIRTIO_F_VERSION_1)) {
> dev_warn(&dev->dev,
> "legacy virtio is incompatible with protected guests");
> return -ENODEV;
> }
>
> if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
> dev_warn(&dev->dev,
> "device does not work with limited memory access in protected guests");
> return -ENODEV;
> }

Yes, easier to read.

Thanks,
Pierre

--
Pierre Morel
IBM Lab Boeblingen