linux-kernel - Re: [PATCH v5 2/2] s390: virtio: PV needs VIRTIO I/O device protection

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Date:   Thu, 9 Jul 2020 12:58:09 +0200
From:   Pierre Morel <pmorel@...ux.ibm.com>
To:     Halil Pasic <pasic@...ux.ibm.com>
Cc:     Cornelia Huck <cohuck@...hat.com>, linux-kernel@...r.kernel.org,
        borntraeger@...ibm.com, frankja@...ux.ibm.com, mst@...hat.com,
        jasowang@...hat.com, kvm@...r.kernel.org,
        linux-s390@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, thomas.lendacky@....com,
        david@...son.dropbear.id.au, linuxram@...ibm.com,
        heiko.carstens@...ibm.com, gor@...ux.ibm.com
Subject: Re: [PATCH v5 2/2] s390: virtio: PV needs VIRTIO I/O device
 protection



On 2020-07-09 11:55, Halil Pasic wrote:
> On Thu, 9 Jul 2020 10:57:33 +0200
> Cornelia Huck <cohuck@...hat.com> wrote:
> 
>> On Thu,  9 Jul 2020 10:39:19 +0200
>> Pierre Morel <pmorel@...ux.ibm.com> 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
> 
> Punctuation at the end?
> 
> Also 'that's not the case' refers to the negation
> 'VIRTIO_F_IOMMU_PLATFORM has been negotiated',
> arch_validate_virtio_features() is however part of
> virtio_finalize_features(), which is in turn part of the feature
> negotiation. But that is details. I'm fine with keeping the message as
> is.
> 
>>>
>>> Signed-off-by: Pierre Morel <pmorel@...ux.ibm.com>
>>> ---
>>>   arch/s390/mm/init.c | 27 +++++++++++++++++++++++++++
>>>   1 file changed, 27 insertions(+)
>>>
>>> diff --git a/arch/s390/mm/init.c b/arch/s390/mm/init.c
>>> index 6dc7c3b60ef6..b8e6f90117da 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 +162,32 @@ 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, "device must provide VIRTIO_F_VERSION_1\n");
>>
>> I'd probably use "legacy virtio not supported with protected
>> virtualization".
>>
>>> +		return -ENODEV;
>>> +	}
>>> +
>>> +	if (!virtio_has_feature(dev, VIRTIO_F_IOMMU_PLATFORM)) {
>>> +		dev_warn(&dev->dev,
>>> +			 "device must provide VIRTIO_F_IOMMU_PLATFORM\n");
>>
>> "support for limited memory access required for protected
>> virtualization"
>>
>> ?
>>
>> Mentioning the feature flag is shorter in both cases, though.
> 
> I liked the messages in v4. Why did we change those? Did somebody
> complain?
> 
> I prefer the old ones, but it any case:
> 
> Acked-by: Halil Pasic <pasic@...ux.ibm.com>

Thanks,
Pierre


-- 
Pierre Morel
IBM Lab Boeblingen