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SubjectRe: [PATCH 01/12] iommu/vt-d: Add cache tag assignment interface
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On 2024/4/10 23:41, Jason Gunthorpe wrote:
> On Mon, Mar 25, 2024 at 10:16:54AM +0800, Lu Baolu wrote:
>> Caching tag is a combination of tags used by the hardware to cache various
>> translations. Whenever a mapping in a domain is changed, the IOMMU driver
>> should invalidate the caches with the caching tags. The VT-d specification
>> describes caching tags in section 6.2.1, Tagging of Cached Translations.
>>
>> Add interface to assign caching tags to an IOMMU domain when attached to a
>> RID or PASID, and unassign caching tags when a domain is detached from a
>> RID or PASID. All caching tags are listed in the per-domain tag list and
>> are protected by a dedicated lock.
>>
>> In addition to the basic IOTLB and devTLB caching tag types, PARENT_IOTLB
>> and PARENT_DEVTLB tag types are also introduced. These tags are used for
>> caches that store translations for DMA accesses through a nested user
>> domain. They are affected by changes to mappings in the parent domain.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>> drivers/iommu/intel/iommu.h | 25 +++++
>> drivers/iommu/intel/cache.c | 192 +++++++++++++++++++++++++++++++++++
>> drivers/iommu/intel/iommu.c | 31 +++++-
>> drivers/iommu/intel/nested.c | 21 +++-
>> drivers/iommu/intel/svm.c | 12 ++-
>> drivers/iommu/intel/Makefile | 2 +-
>> 6 files changed, 274 insertions(+), 9 deletions(-)
>> create mode 100644 drivers/iommu/intel/cache.c
>>
>> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
>> index 404d2476a877..e3723b7a0b31 100644
>> --- a/drivers/iommu/intel/iommu.h
>> +++ b/drivers/iommu/intel/iommu.h
>> @@ -607,6 +607,9 @@ struct dmar_domain {
>> struct list_head devices; /* all devices' list */
>> struct list_head dev_pasids; /* all attached pasids */
>>
>> + spinlock_t cache_lock; /* Protect the cache tag list */
>> + struct list_head cache_tags; /* Cache tag list */
>
> That is quite a neat trick - though building a dedicated invalidation
> list duplicates data stored in the attached devices list?

Yes. The device and dev_pasid lists appear to be duplicate. I am about
to remove these two lists later.

> You didn't try to make it RCU safe for invalidation?

The queued invalidation interface is a bit complicated, especially when
it comes to device TLB invalidation. Device TLB invalidation might
result in a timeout, which requires special treatment.

>> +struct cache_tag {
>> + struct list_head node;
>> + enum cache_tag_type type;
>> + struct intel_iommu *iommu;
>> + struct device *dev;
>
> iommu and dev probably don't both need to be stored together. We have
> iommu_get_iommu_dev() now.. I suppose this is probably a union of the
> two pointers depending on tag. DEVTLB needs the dev and IOTLB needs
> the iommu.
>
>> + u16 domain_id;
>> + ioasid_t pasid;
>> + int users;
>
> unsigned int

Sure.

>
>> +static int __cache_tag_assign_parent_domain(struct dmar_domain *domain, u16 did,
>> + struct device *dev, ioasid_t pasid)
>> +{
>> + struct device_domain_info *info = dev_iommu_priv_get(dev);
>> + int ret;
>> +
>> + ret = cache_tag_assign(domain, did, dev, pasid, CACHE_TAG_TYPE_PARENT_IOTLB);
>> + if (ret || !info->ats_enabled)
>> + return ret;
>
> I'm not sure I understood the point of PARENT_IOTLB? I didn't see any
> different implementation?
>
> Isn't this backwards though? Each domain should have a list of things
> to invalidate if the domain itself changes.
>
> So the nesting parent should have a list of CHILD_DEVTLB's that need
> cleaning. That list is changed when the nesting domains are attached
> to something.
>
> And a list of CHILD_IOTLBs, but the HW doesn't seem to need that?

This is a partial replacement of below series.

https://lore.kernel.org/all/20240208082307.15759-1-yi.l.liu@intel.com/

Best regards,
baolu


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