Re: [RFC v2 1/5] vfio/type1: Introduce iova list and add iommu aperture validity check

[Auger Eric]

Hi Shameer,

On 23/01/18 11:04, Shameerali Kolothum Thodi wrote:
> Hi Eric,
> 
>> -----Original Message-----
>> From: Auger Eric [mailto:eric.auger@xxxxxxxxxx]
>> Sent: Tuesday, January 23, 2018 8:25 AM
>> To: Alex Williamson <alex.williamson@xxxxxxxxxx>; Shameerali Kolothum
>> Thodi <shameerali.kolothum.thodi@xxxxxxxxxx>
>> Cc: pmorel@xxxxxxxxxxxxxxxxxx; kvm@xxxxxxxxxxxxxxx; linux-
>> kernel@xxxxxxxxxxxxxxx; Linuxarm <linuxarm@xxxxxxxxxx>; John Garry
>> <john.garry@xxxxxxxxxx>; xuwei (O) <xuwei5@xxxxxxxxxx>
>> Subject: Re: [RFC v2 1/5] vfio/type1: Introduce iova list and add iommu
>> aperture validity check
>>
>> Hi Shameer,
>>
>> On 18/01/18 01:04, Alex Williamson wrote:
>>> On Fri, 12 Jan 2018 16:45:27 +0000
>>> Shameer Kolothum <shameerali.kolothum.thodi@xxxxxxxxxx> wrote:
>>>
>>>> This introduces an iova list that is valid for dma mappings. Make
>>>> sure the new iommu aperture window is valid and doesn't conflict
>>>> with any existing dma mappings during attach. Also update the iova
>>>> list with new aperture window during attach/detach.
>>>>
>>>> Signed-off-by: Shameer Kolothum
>> <shameerali.kolothum.thodi@xxxxxxxxxx>
>>>> ---
>>>>  drivers/vfio/vfio_iommu_type1.c | 177
>> ++++++++++++++++++++++++++++++++++++++++
>>>>  1 file changed, 177 insertions(+)
>>>>
>>>> diff --git a/drivers/vfio/vfio_iommu_type1.c
>> b/drivers/vfio/vfio_iommu_type1.c
>>>> index e30e29a..11cbd49 100644
>>>> --- a/drivers/vfio/vfio_iommu_type1.c
>>>> +++ b/drivers/vfio/vfio_iommu_type1.c
>>>> @@ -60,6 +60,7 @@
>>>>
>>>>  struct vfio_iommu {
>>>>  	struct list_head	domain_list;
>>>> +	struct list_head	iova_list;
>>>>  	struct vfio_domain	*external_domain; /* domain for external user
>> */
>>>>  	struct mutex		lock;
>>>>  	struct rb_root		dma_list;
>>>> @@ -92,6 +93,12 @@ struct vfio_group {
>>>>  	struct list_head	next;
>>>>  };
>>>>
>>>> +struct vfio_iova {
>>>> +	struct list_head	list;
>>>> +	phys_addr_t		start;
>>>> +	phys_addr_t		end;
>>>> +};
>>>
>>> dma_list uses dma_addr_t for the iova.  IOVAs are naturally DMA
>>> addresses, why are we using phys_addr_t?
>>>
>>>> +
>>>>  /*
>>>>   * Guest RAM pinning working set or DMA target
>>>>   */
>>>> @@ -1192,6 +1199,123 @@ static bool vfio_iommu_has_sw_msi(struct
>> iommu_group *group, phys_addr_t *base)
>>>>  	return ret;
>>>>  }
>>>>
>>>> +static int vfio_insert_iova(phys_addr_t start, phys_addr_t end,
>>>> +				struct list_head *head)
>>>> +{
>>>> +	struct vfio_iova *region;
>>>> +
>>>> +	region = kmalloc(sizeof(*region), GFP_KERNEL);
>>>> +	if (!region)
>>>> +		return -ENOMEM;
>>>> +
>>>> +	INIT_LIST_HEAD(&region->list);
>>>> +	region->start = start;
>>>> +	region->end = end;
>>>> +
>>>> +	list_add_tail(&region->list, head);
>>>> +	return 0;
>>>> +}
>>>
>>> As I'm reading through this series, I'm learning that there are a lot
>>> of assumptions and subtle details that should be documented.  For
>>> instance, the IOMMU API only provides a single geometry and we build
>>> upon that here as this patch creates a list, but there's only a single
>>> entry for now.  The following patches carve that single iova range into
>>> pieces and somewhat subtly use the list_head passed to keep the list
>>> sorted, allowing the first/last_entry tricks used throughout.  Subtle
>>> interfaces are prone to bugs.
>>>
>>>> +
>>>> +/*
>>>> + * Find whether a mem region overlaps with existing dma mappings
>>>> + */
>>>> +static bool vfio_find_dma_overlap(struct vfio_iommu *iommu,
>>>> +				  phys_addr_t start, phys_addr_t end)
>>>> +{
>>>> +	struct rb_node *n = rb_first(&iommu->dma_list);
>>>> +
>>>> +	for (; n; n = rb_next(n)) {
>>>> +		struct vfio_dma *dma;
>>>> +
>>>> +		dma = rb_entry(n, struct vfio_dma, node);
>>>> +
>>>> +		if (end < dma->iova)
>>>> +			break;
>>>> +		if (start >= dma->iova + dma->size)
>>>> +			continue;
>>>> +		return true;
>>>> +	}
>>>> +
>>>> +	return false;
>>>> +}
>>>
>>> Why do we need this in addition to the existing vfio_find_dma()?  Why
>>> doesn't this use the tree structure of the dma_list?
>>>
>>>> +
>>>> +/*
>>>> + * Check the new iommu aperture is a valid one
>>>> + */
>>>> +static int vfio_iommu_valid_aperture(struct vfio_iommu *iommu,
>>>> +				     phys_addr_t start,
>>>> +				     phys_addr_t end)
>>>> +{
>>>> +	struct vfio_iova *first, *last;
>>>> +	struct list_head *iova = &iommu->iova_list;
>>>> +
>>>> +	if (list_empty(iova))
>>>> +		return 0;
>>>> +
>>>> +	/* Check if new one is outside the current aperture */
>>>
>>> "Disjoint sets"
>>>
>>>> +	first = list_first_entry(iova, struct vfio_iova, list);
>>>> +	last = list_last_entry(iova, struct vfio_iova, list);
>>>> +	if ((start > last->end) || (end < first->start))
>>>> +		return -EINVAL;
>>>> +
>>>> +	/* Check for any existing dma mappings outside the new start */
>>>> +	if (start > first->start) {
>>>> +		if (vfio_find_dma_overlap(iommu, first->start, start - 1))
>>>> +			return -EINVAL;
>>>> +	}
>>>> +
>>>> +	/* Check for any existing dma mappings outside the new end */
>>>> +	if (end < last->end) {
>>>> +		if (vfio_find_dma_overlap(iommu, end + 1, last->end))
>>>> +			return -EINVAL;
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>
>>> I think this returns an int because you want to use it for the return
>>> value below, but it really seems like a bool question, ie. does this
>>> aperture conflict with existing mappings.  Additionally, the aperture
>>> is valid, it was provided to us by the IOMMU API, the question is
>>> whether it conflicts.  Please also name consistently to the other
>>> functions in this patch, vfio_iommu_aper_xxxx().
>>>
>>>> +
>>>> +/*
>>>> + * Adjust the iommu aperture window if new aperture is a valid one
>>>> + */
>>>> +static int vfio_iommu_iova_aper_adjust(struct vfio_iommu *iommu,
>>>> +				      phys_addr_t start,
>>>> +				      phys_addr_t end)
>>>
>>> Perhaps "resize", "prune", or "shrink" to make it more clear what is
>>> being adjusted?
>>>
>>>> +{
>>>> +	struct vfio_iova *node, *next;
>>>> +	struct list_head *iova = &iommu->iova_list;
>>>> +
>>>> +	if (list_empty(iova))
>>>> +		return vfio_insert_iova(start, end, iova);
>>>> +
>>>> +	/* Adjust iova list start */
>>>> +	list_for_each_entry_safe(node, next, iova, list) {
>>>> +		if (start < node->start)
>>>> +			break;
>>>> +		if ((start >= node->start) && (start <= node->end)) {
>>>
>>> start == node->end results in a zero sized node.  s/<=/</
>>>
>>>> +			node->start = start;
>>>> +			break;
>>>> +		}
>>>> +		/* Delete nodes before new start */
>>>> +		list_del(&node->list);
>>>> +		kfree(node);
>>>> +	}
>>>> +
>>>> +	/* Adjust iova list end */
>>>> +	list_for_each_entry_safe(node, next, iova, list) {
>>>> +		if (end > node->end)
>>>> +			continue;
>>>> +
>>>> +		if ((end >= node->start) && (end <= node->end)) {
>>>
>>> end == node->start results in a zero sized node.  s/>=/>/
>>>
>>>> +			node->end = end;
>>>> +			continue;
>>>> +		}
>>>> +		/* Delete nodes after new end */
>>>> +		list_del(&node->list);
>>>> +		kfree(node);
>>>> +	}
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +
>>>>  static int vfio_iommu_type1_attach_group(void *iommu_data,
>>>>  					 struct iommu_group *iommu_group)
>>>>  {
>>>> @@ -1202,6 +1326,7 @@ static int vfio_iommu_type1_attach_group(void
>> *iommu_data,
>>>>  	int ret;
>>>>  	bool resv_msi, msi_remap;
>>>>  	phys_addr_t resv_msi_base;
>>>> +	struct iommu_domain_geometry geo;
>>>>
>>>>  	mutex_lock(&iommu->lock);
>>>>
>>>> @@ -1271,6 +1396,14 @@ static int vfio_iommu_type1_attach_group(void
>> *iommu_data,
>>>>  	if (ret)
>>>>  		goto out_domain;
>>>>
>>>> +	/* Get aperture info */
>>>> +	iommu_domain_get_attr(domain->domain,
>> DOMAIN_ATTR_GEOMETRY, &geo);
>>>> +
>>>> +	ret = vfio_iommu_valid_aperture(iommu, geo.aperture_start,
>>>> +					geo.aperture_end);
>>>> +	if (ret)
>>>> +		goto out_detach;
>>>> +
>>>>  	resv_msi = vfio_iommu_has_sw_msi(iommu_group, &resv_msi_base);
>>>>
>>>>  	INIT_LIST_HEAD(&domain->group_list);
>>>> @@ -1327,6 +1460,11 @@ static int vfio_iommu_type1_attach_group(void
>> *iommu_data,
>>>>  			goto out_detach;
>>>>  	}
>>>>
>>>> +	ret = vfio_iommu_iova_aper_adjust(iommu, geo.aperture_start,
>>>> +					  geo.aperture_end);
>>>> +	if (ret)
>>>> +		goto out_detach;
>>>> +
>>>>  	list_add(&domain->next, &iommu->domain_list);
>>>>
>>>>  	mutex_unlock(&iommu->lock);
>>>> @@ -1392,6 +1530,35 @@ static void vfio_sanity_check_pfn_list(struct
>> vfio_iommu *iommu)
>>>>  	WARN_ON(iommu->notifier.head);
>>>>  }
>>>>
>>>> +/*
>>>> + * Called when a domain is removed in detach. It is possible that
>>>> + * the removed domain decided the iova aperture window. Modify the
>>>> + * iova aperture with the smallest window among existing domains.
>>>> + */
>>>> +static void vfio_iommu_iova_aper_refresh(struct vfio_iommu *iommu)
>>>> +{
>>>> +	struct vfio_domain *domain;
>>>> +	struct iommu_domain_geometry geo;
>>>> +	struct vfio_iova *node;
>>>> +	phys_addr_t start = 0;
>>>> +	phys_addr_t end = (phys_addr_t)~0;
>>>> +
>>>> +	list_for_each_entry(domain, &iommu->domain_list, next) {
>>>> +		iommu_domain_get_attr(domain->domain,
>> DOMAIN_ATTR_GEOMETRY,
>>>> +				      &geo);
>>>> +			if (geo.aperture_start > start)
>>>> +				start = geo.aperture_start;
>>>> +			if (geo.aperture_end < end)
>>>> +				end = geo.aperture_end;
>>>> +	}
>>>> +
>>>> +	/* modify iova aperture limits */
>>>> +	node = list_first_entry(&iommu->iova_list, struct vfio_iova, list);
>>>> +	node->start = start;
>>>> +	node = list_last_entry(&iommu->iova_list, struct vfio_iova, list);
>>>> +	node->end = end;
>>>
>>> We can do this because the new aperture is the same or bigger than the
>>> current aperture, never smaller.  That's not fully obvious and should
>>> be noted in the comment.  Perhaps this function should be "expand"
>>> rather than "refresh".
>> This one is not obvious to me either:
>> assuming you have 2 domains, resp with aperture 1 and 2, resulting into
>> aperture 3. Holes are created by resv regions for instance. If you
>> remove domain 1, don't you get 4) instead of 2)?
>>
>> 1)   |------------|
>>  +
>> 2) |---|    |--|       |-----|
>> =
>> 3)   |-|    |--|
>>
>>
>> 4) |---|    |----------------|
> 
> That is true partially. But please remember that this patch is not aware of
> any reserved regions yet. That is introduced in patch #2. So patch #1 and #2
> together, the iova aperture might looks like 4) after this function call and once 
> vfio_iommu_iova_resv_refresh() in patch #2 is done, the aperture will be
> back to 2).
> 
> Hope I am clear. Please let me know.
Ah OK.
> 
> In any case, based on comments by Alex, I will be removing this aperture/reserve
> refresh functions and leave the iova list as it is when a group is detached. 
Looking forwarding to reviewing the next version then.

Thanks

Eric
> 
> Thanks,
> Shameer
> 
>> Thanks
>>
>> Eric
>>>
>>>> +}
>>>> +
>>>>  static void vfio_iommu_type1_detach_group(void *iommu_data,
>>>>  					  struct iommu_group *iommu_group)
>>>>  {
>>>> @@ -1445,6 +1612,7 @@ static void vfio_iommu_type1_detach_group(void
>> *iommu_data,
>>>>  			iommu_domain_free(domain->domain);
>>>>  			list_del(&domain->next);
>>>>  			kfree(domain);
>>>> +			vfio_iommu_iova_aper_refresh(iommu);
>>>>  		}
>>>>  		break;
>>>>  	}
>>>> @@ -1475,6 +1643,7 @@ static void *vfio_iommu_type1_open(unsigned
>> long arg)
>>>>  	}
>>>>
>>>>  	INIT_LIST_HEAD(&iommu->domain_list);
>>>> +	INIT_LIST_HEAD(&iommu->iova_list);
>>>>  	iommu->dma_list = RB_ROOT;
>>>>  	mutex_init(&iommu->lock);
>>>>  	BLOCKING_INIT_NOTIFIER_HEAD(&iommu->notifier);
>>>> @@ -1502,6 +1671,7 @@ static void vfio_iommu_type1_release(void
>> *iommu_data)
>>>>  {
>>>>  	struct vfio_iommu *iommu = iommu_data;
>>>>  	struct vfio_domain *domain, *domain_tmp;
>>>> +	struct vfio_iova *iova, *iova_tmp;
>>>>
>>>>  	if (iommu->external_domain) {
>>>>  		vfio_release_domain(iommu->external_domain, true);
>>>> @@ -1517,6 +1687,13 @@ static void vfio_iommu_type1_release(void
>> *iommu_data)
>>>>  		list_del(&domain->next);
>>>>  		kfree(domain);
>>>>  	}
>>>> +
>>>> +	list_for_each_entry_safe(iova, iova_tmp,
>>>> +				 &iommu->iova_list, list) {
>>>> +		list_del(&iova->list);
>>>> +		kfree(iova);
>>>> +	}
>>>> +
>>>>  	kfree(iommu);
>>>>  }
>>>>
>>>