Re: [PATCH 1/1] iommu/vt-d: Support asynchronous IOMMU nested capabilities

[Lu Baolu <baolu.lu@linux.intel.com>]

Hi Kevin,

On 5/12/21 4:30 PM, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Wednesday, May 12, 2021 3:04 PM
>>
>> Current VT-d implementation supports nested translation only if all
>> underlying IOMMUs support the nested capability. This is unnecessary
>> as the upper layer is allowed to create different containers and set
>> them with different type of iommu backend. The IOMMU driver needs to
>> guarantee that devices attached to a nested mode iommu_domain should
>> support nested capabilility.
> 
> so the consistency check is now applied only to the IOMMUs that are
> spanned by a given iommu_domain?

Yes.

> 
>>
>> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
>> ---
>>   drivers/iommu/intel/iommu.c | 21 +++++++++++++++++++--
>>   1 file changed, 19 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
>> index f1742da42478..1cd4840e6f9f 100644
>> --- a/drivers/iommu/intel/iommu.c
>> +++ b/drivers/iommu/intel/iommu.c
>> @@ -4755,6 +4755,13 @@ static int prepare_domain_attach_device(struct
>> iommu_domain *domain,
>>   	if (!iommu)
>>   		return -ENODEV;
>>
>> +	if ((dmar_domain->flags & DOMAIN_FLAG_NESTING_MODE) &&
>> +	    !ecap_nest(iommu->ecap)) {
>> +		dev_err(dev, "%s: iommu not support nested translation\n",
>> +			iommu->name);
>> +		return -EINVAL;
>> +	}
>> +
>>   	/* check if this iommu agaw is sufficient for max mapped address */
>>   	addr_width = agaw_to_width(iommu->agaw);
>>   	if (addr_width > cap_mgaw(iommu->cap))
>> @@ -5451,11 +5458,21 @@ static int
>>   intel_iommu_enable_nesting(struct iommu_domain *domain)
>>   {
>>   	struct dmar_domain *dmar_domain = to_dmar_domain(domain);
>> +	struct dmar_drhd_unit *drhd;
>> +	struct intel_iommu *iommu;
>> +	bool has_nesting = false;
>>   	unsigned long flags;
>> -	int ret = -ENODEV;
>> +	int ret = -EINVAL;
>> +
>> +	for_each_active_iommu(iommu, drhd)
>> +		if (ecap_nest(iommu->ecap))
>> +			has_nesting = true;
>> +
>> +	if (!has_nesting)
>> +		return -ENODEV;
> 
> Isn't above still doing global consistency check?

The logic is if nested mode is globally unsupported, return false.

> 
>>
>>   	spin_lock_irqsave(&device_domain_lock, flags);
>> -	if (nested_mode_support() && list_empty(&dmar_domain->devices))
>> {
>> +	if (list_empty(&dmar_domain->devices)) {
>>   		dmar_domain->flags |= DOMAIN_FLAG_NESTING_MODE;
>>   		dmar_domain->flags &= ~DOMAIN_FLAG_USE_FIRST_LEVEL;
>>   		ret = 0;
>> --
>> 2.25.1
> 

Best regards,
baolu