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SubjectRe: [PATCH 01/12] iommu/vt-d: Add cache tag assignment interface
Hi Kevin,

Thanks for your review comments.

On 3/28/24 3:12 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Monday, March 25, 2024 10:17 AM
>>
>> +enum cache_tag_type {
>> + CACHE_TAG_TYPE_IOTLB,
>> + CACHE_TAG_TYPE_DEVTLB,
>> + CACHE_TAG_TYPE_PARENT_IOTLB,
>> + CACHE_TAG_TYPE_PARENT_DEVTLB,
>> +};
>
> '_TYPE_' can be removed to make it shorter

Okay.

>
>> +
>> +/* Checks if an existing cache tag can be reused for a new association. */
>> +static bool cache_tag_reusable(struct cache_tag *tag, u16 domain_id,
>> + struct intel_iommu *iommu, struct device *dev,
>> + ioasid_t pasid, enum cache_tag_type type)
>
> cache_tage_match()

Okay.

>
>> +{
>> + if (tag->type != type)
>> + return false;
>> +
>> + if (tag->domain_id != domain_id || tag->pasid != pasid)
>> + return false;
>> +
>> + if (type == CACHE_TAG_TYPE_IOTLB)
>> + return tag->iommu == iommu;
>> +
>> + if (type == CACHE_TAG_TYPE_DEVTLB)
>> + return tag->dev == dev;
>> +
>> + return false;
>
> why do you disallow PARENT_TYPE from reusing? It's not uncommon
> to have two devices attached to a same nested domain hence with
> the same parent domain. Disallowing tag reuse implies unnecessarily
> duplicated cache flushes...

PARENT_TYPE could be reused. The new helper looks like the following:

/* Checks if an existing cache tag can be reused for a new association. */
static bool cache_tage_match(struct cache_tag *tag, u16 domain_id,
struct intel_iommu *iommu, struct device
*dev,
ioasid_t pasid, enum cache_tag_type type)
{
if (tag->type != type)
return false;

if (tag->domain_id != domain_id || tag->pasid != pasid)
return false;

if (type == CACHE_TAG_IOTLB || type == CACHE_TAG_PARENT_IOTLB)
return tag->iommu == iommu;

if (type == CACHE_TAG_DEVTLB || type == CACHE_TAG_PARENT_DEVTLB)
return tag->dev == dev;

return false;
}

>> +}
>> +
>> +/* Assign a cache tag with specified type to domain. */
>> +static int cache_tag_assign(struct dmar_domain *domain, u16 did,
>> + struct device *dev, ioasid_t pasid,
>> + enum cache_tag_type type)
>> +{
>> + struct device_domain_info *info = dev_iommu_priv_get(dev);
>> + struct intel_iommu *iommu = info->iommu;
>> + struct cache_tag *tag, *temp;
>> + unsigned long flags;
>> +
>> + tag = kzalloc(sizeof(*tag), GFP_KERNEL);
>> + if (!tag)
>> + return -ENOMEM;
>> +
>> + tag->type = type;
>> + tag->iommu = iommu;
>> + tag->dev = dev;
>
> should we set tag->dev only for DEVTLB type? It's a bit confusing to set
> it for IOTLB type which doesn't care about device. Actually doing so
> is instead misleading as the 1st device creating the tag may have been
> detached but then it will still show up in the trace when the last device
> detach destroying the tag.

For IOTLB types, perhaps we could add a struct device pointer for the
iommu. This way, the tag->dev could more directly indicate the device
implementing the cache.

>
>> +static int __cache_tag_assign_parent_domain(struct dmar_domain
>> *domain, u16 did,
>> + struct device *dev, ioasid_t pasid)
>
> this pair is similar to the earlier one except the difference on type.
>
> what about keeping just one pair which accepts a 'parent' argument to
> decide the type internally?

Okay, let try to refine it.

>
>
>> +/*
>> + * Assigns cache tags to a domain when it's associated with a device's
>> + * PASID using a specific domain ID.
>
> s/Assigns/Assign/

Done.

>
>> +
>> + did = domain_id_iommu(domain, iommu);
>> + ret = cache_tag_assign_domain(domain, did, dev,
>> IOMMU_NO_PASID);
>
> there are many occurrences of this pattern. What about passing in
> a 'iommu' parameter and getting 'did' inside the helper? for svm
> it can be specialized internally too.

Perhaps, let me try it later and see what the code looks like.

>
>> @@ -4607,10 +4623,11 @@ static void
>> intel_iommu_remove_dev_pasid(struct device *dev, ioasid_t pasid)
>> */
>> if (domain->type == IOMMU_DOMAIN_SVA) {
>> intel_svm_remove_dev_pasid(dev, pasid);
>> + cache_tag_unassign_domain(dmar_domain,
>> + FLPT_DEFAULT_DID, dev, pasid);
>
> is it correct to destroy the tag before teardown completes, e.g. iotlb still
> needs to be flushed in intel_pasid_tear_down_entry()?

You are right. iotlb still needs to be there until the teardown
completes. I will investigate this more later.

Beset regards,
baolu

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