Subject: Re: [PATCH kernel v6 26/29] vfio: powerpc/spapr: Define v2 IOMMU

From: Alexey Kardashevskiy <[email-masked]>
Date: Tue, 17 Mar 2015 13:59:41 +1100

On 03/17/2015 06:45 AM, Alex Williamson wrote:
> On Fri, 2015-03-13 at 19:07 +1100, Alexey Kardashevskiy wrote:
>> The existing IOMMU requires VFIO_IOMMU_ENABLE call to enable actual use
>> of the container (i.e. call DMA map/unmap) and this is where we check
>> the rlimit for locked pages. It assumes that only as much memory
>> as a default DMA window can be mapped. Every DMA map/unmap request will
>> do pinning/unpinning of physical pages.
>>
>> New IOMMU will split physical pages pinning and TCE table update.
>> It will require guest pages to be registered first and consequent
>> map/unmap requests to work only with pre-registered memory.
>> For the default single window case this means that the entire guest
>> (instead of 2GB) needs to be pinned before using VFIO.
>> However when a huge DMA window is added, no additional pinning will be
>> required, otherwise it would be guest RAM + 2GB.
>>
>> This advertises v2 SPAPR TCE IOMMU and restricts what the userspace
>> can do with v1 or v2 IOMMUs.
>>
>> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
>> ---
>> Changes:
>> v6:
>> * enforced limitations imposed by the SPAPR TCE IOMMU version
>> ---
>>   drivers/vfio/vfio_iommu_spapr_tce.c | 18 +++++++++++++++++-
>>   include/uapi/linux/vfio.h           |  2 ++
>>   2 files changed, 19 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
>> index 9d240b4..e191438 100644
>> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
>> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
>> @@ -95,6 +95,7 @@ struct tce_container {
>>   	bool enabled;
>>   	unsigned long locked_pages;
>>   	struct list_head mem_list;
>> +	bool v2;
>>   };
>>
>>   struct tce_memory {
>> @@ -398,7 +399,7 @@ static void *tce_iommu_open(unsigned long arg)
>>   {
>>   	struct tce_container *container;
>>
>> -	if (arg != VFIO_SPAPR_TCE_IOMMU) {
>> +	if ((arg != VFIO_SPAPR_TCE_IOMMU) && (arg != VFIO_SPAPR_TCE_v2_IOMMU)) {
>>   		pr_err("tce_vfio: Wrong IOMMU type\n");
>>   		return ERR_PTR(-EINVAL);
>>   	}
>> @@ -410,6 +411,8 @@ static void *tce_iommu_open(unsigned long arg)
>>   	mutex_init(&container->lock);
>>   	INIT_LIST_HEAD_RCU(&container->mem_list);
>>
>> +	container->v2 = arg == VFIO_SPAPR_TCE_v2_IOMMU;
>> +
>>   	return container;
>>   }
>>
>> @@ -580,6 +583,7 @@ static long tce_iommu_ioctl(void *iommu_data,
>>   	case VFIO_CHECK_EXTENSION:
>>   		switch (arg) {
>>   		case VFIO_SPAPR_TCE_IOMMU:
>> +		case VFIO_SPAPR_TCE_v2_IOMMU:
>>   			ret = 1;
>>   			break;
>>   		default:
>> @@ -719,6 +723,9 @@ static long tce_iommu_ioctl(void *iommu_data,
>>   	case VFIO_IOMMU_SPAPR_REGISTER_MEMORY: {
>>   		struct vfio_iommu_spapr_register_memory param;
>>
>> +		if (!container->v2)
>> +			return -EPERM;
>> +
>>   		minsz = offsetofend(struct vfio_iommu_spapr_register_memory,
>>   				size);
>>
>> @@ -741,6 +748,9 @@ static long tce_iommu_ioctl(void *iommu_data,
>>   	case VFIO_IOMMU_SPAPR_UNREGISTER_MEMORY: {
>>   		struct vfio_iommu_spapr_register_memory param;
>>
>> +		if (!container->v2)
>> +			return -EPERM;
>> +
>>   		minsz = offsetofend(struct vfio_iommu_spapr_register_memory,
>>   				size);
>>
>> @@ -761,6 +771,9 @@ static long tce_iommu_ioctl(void *iommu_data,
>>   		return 0;
>>   	}
>>   	case VFIO_IOMMU_ENABLE:
>> +		if (container->v2)
>> +			return -EPERM;
>> +
>>   		mutex_lock(&container->lock);
>>   		ret = tce_iommu_enable(container);
>>   		mutex_unlock(&container->lock);
>> @@ -768,6 +781,9 @@ static long tce_iommu_ioctl(void *iommu_data,
>>
>>
>>   	case VFIO_IOMMU_DISABLE:
>> +		if (container->v2)
>> +			return -EPERM;
>> +
>>   		mutex_lock(&container->lock);
>>   		tce_iommu_disable(container);
>>   		mutex_unlock(&container->lock);
>
>
> I wouldn't have guessed; nothing in the documentation suggests these
> ioctls are deprecated in v2 (ie. please document).  If the ioctl doesn't
> exist for the IOMMU type, why not simply break and let it fall out at
> -ENOTTY?  Same for the above, v1 would have previously returned -ENOTTY
> for those ioctls, why change to -EPERM?

Good points. I'll fix them and merge this patch to "vfio: powerpc/spapr: 
Register memory" as this is where it actually belongs to. Agree?

Thanks for the review!

-- 
Alexey