Re: [PATCH 3/4] iommu/vt-d: Allow IOMMU_DOMAIN_DMA and IOMMU_DOMAIN_IDENTITY to be allocated

[James Sewart <jamessewart@arista.com>]

Hey Lu,

> On 5 Mar 2019, at 06:46, Lu Baolu <baolu.lu@linux.intel.com> wrote:
> 
> Hi,
> 
> On 3/4/19 11:46 PM, James Sewart wrote:
>> Allowing IOMMU_DOMAIN_DMA type IOMMU domain to be allocated allows the
>> default_domain of an iommu_group to be set. This delegates device-domain
>> relationships to the generic IOMMU code.
>> Signed-off-by: James Sewart <jamessewart@arista.com>
>> ---
>>  drivers/iommu/intel-iommu.c | 113 +++++++++++++++++++++++++++---------
>>  1 file changed, 84 insertions(+), 29 deletions(-)
>> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
>> index 8e0a4e2ff77f..71cd6bbfec05 100644
>> --- a/drivers/iommu/intel-iommu.c
>> +++ b/drivers/iommu/intel-iommu.c
>> @@ -309,6 +309,14 @@ static int hw_pass_through = 1;
>>  /* si_domain contains mulitple devices */
>>  #define DOMAIN_FLAG_STATIC_IDENTITY	(1 << 1)
>>  +/* Domain managed externally, don't cleanup if it isn't attached
>> + * to any devices. */
>> +#define DOMAIN_FLAG_MANAGED_EXTERNALLY	(1 << 2)
>> +
>> +/* Set after domain initialisation. Used when allocating dma domains to
>> + * defer domain initialisation until it is attached to a device */
>> +#define DOMAIN_FLAG_INITIALISED	(1 << 4)
> 
> Why do you skip bit 3?

This was an oversight, I will update to use bit 3.

> 
>> +
>>  #define for_each_domain_iommu(idx, domain)			\
>>  	for (idx = 0; idx < g_num_of_iommus; idx++)		\
>>  		if (domain->iommu_refcnt[idx])
>> @@ -558,6 +566,16 @@ static inline int domain_type_is_vm_or_si(struct dmar_domain *domain)
>>  				DOMAIN_FLAG_STATIC_IDENTITY);
>>  }
>>  +static inline int domain_managed_externally(struct dmar_domain *domain)
>> +{
>> +	return domain->flags & DOMAIN_FLAG_MANAGED_EXTERNALLY;
>> +}
>> +
>> +static inline int domain_is_initialised(struct dmar_domain *domain)
>> +{
>> +	return domain->flags & DOMAIN_FLAG_INITIALISED;
>> +}
>> +
>>  static inline int domain_pfn_supported(struct dmar_domain *domain,
>>  				       unsigned long pfn)
>>  {
>> @@ -1662,7 +1680,7 @@ static void disable_dmar_iommu(struct intel_iommu *iommu)
>>    		__dmar_remove_one_dev_info(info);
>>  -		if (!domain_type_is_vm_or_si(domain)) {
>> +		if (!domain_managed_externally(domain)) {
>>  			/*
>>  			 * The domain_exit() function  can't be called under
>>  			 * device_domain_lock, as it takes this lock itself.
>> @@ -1895,6 +1913,7 @@ static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
>>  	domain->pgd = (struct dma_pte *)alloc_pgtable_page(domain->nid);
>>  	if (!domain->pgd)
>>  		return -ENOMEM;
>> +	domain->flags |= DOMAIN_FLAG_INITIALISED;
>>  	__iommu_flush_cache(iommu, domain->pgd, PAGE_SIZE);
>>  	return 0;
>>  }
>> @@ -2807,14 +2826,10 @@ static inline void iommu_prepare_isa(void)
>>    static int md_domain_init(struct dmar_domain *domain, int guest_width);
>>  -static int __init si_domain_init(int hw)
>> +static int __init si_domain_init(struct dmar_domain *si_domain, int hw)
>>  {
>>  	int nid, ret = 0;
>>  -	si_domain = alloc_domain(DOMAIN_FLAG_STATIC_IDENTITY);
>> -	if (!si_domain)
>> -		return -EFAULT;
>> -
>>  	if (md_domain_init(si_domain, DEFAULT_DOMAIN_ADDRESS_WIDTH)) {
>>  		domain_exit(si_domain);
>>  		return -EFAULT;
>> @@ -3417,9 +3432,16 @@ static int __init init_dmars(void)
>>  	check_tylersburg_isoch();
>>    	if (iommu_identity_mapping) {
>> -		ret = si_domain_init(hw_pass_through);
>> -		if (ret)
>> +		si_domain = alloc_domain(DOMAIN_FLAG_STATIC_IDENTITY);
> 
> Where will this si_domain be used? We still need to keep the global
> si_domain?

I am unsure of the best thing to do here. The si_domain can be initialised 
as a hardware passthrough which means it doesn’t have any mappings applied. 
I think any user allocating a domain here will always want a software 
passthrough domain. I’m not sure if/how to consolidate these two.

> 
>> +		if (!si_domain) {
>> +			ret = -EFAULT;
>>  			goto free_iommu;
>> +		}
>> +		ret = si_domain_init(si_domain, hw_pass_through);
>> +		if (ret) {
>> +			domain_exit(si_domain);
>> +			goto free_iommu;
>> +		}
>>  	}
>>    @@ -4575,7 +4597,7 @@ static int device_notifier(struct notifier_block *nb,
>>  		return 0;
>>    	dmar_remove_one_dev_info(domain, dev);
>> -	if (!domain_type_is_vm_or_si(domain) && list_empty(&domain->devices))
>> +	if (!domain_managed_externally(domain) && list_empty(&domain->devices))
>>  		domain_exit(domain);
>>    	return 0;
>> @@ -5020,6 +5042,7 @@ static int md_domain_init(struct dmar_domain *domain, int guest_width)
>>  	domain->pgd = (struct dma_pte *)alloc_pgtable_page(domain->nid);
>>  	if (!domain->pgd)
>>  		return -ENOMEM;
>> +	domain->flags |= DOMAIN_FLAG_INITIALISED;
>>  	domain_flush_cache(domain, domain->pgd, PAGE_SIZE);
>>  	return 0;
>>  }
>> @@ -5028,28 +5051,54 @@ static struct iommu_domain *intel_iommu_domain_alloc(unsigned type)
>>  {
>>  	struct dmar_domain *dmar_domain;
>>  	struct iommu_domain *domain;
>> +	int flags = DOMAIN_FLAG_MANAGED_EXTERNALLY;
>>  -	if (type != IOMMU_DOMAIN_UNMANAGED)
>> -		return NULL;
>> -
>> -	dmar_domain = alloc_domain(DOMAIN_FLAG_VIRTUAL_MACHINE);
>> -	if (!dmar_domain) {
>> -		pr_err("Can't allocate dmar_domain\n");
>> -		return NULL;
>> -	}
>> -	if (md_domain_init(dmar_domain, DEFAULT_DOMAIN_ADDRESS_WIDTH)) {
>> -		pr_err("Domain initialization failed\n");
>> -		domain_exit(dmar_domain);
>> +	switch (type) {
>> +	case IOMMU_DOMAIN_UNMANAGED:
>> +		flags |= DOMAIN_FLAG_VIRTUAL_MACHINE | DOMAIN_FLAG_INITIALISED;
>> +		dmar_domain = alloc_domain(flags);
>> +		if (!dmar_domain) {
>> +			pr_err("Can't allocate dmar_domain\n");
>> +			return NULL;
>> +		}
>> +		if (md_domain_init(dmar_domain, DEFAULT_DOMAIN_ADDRESS_WIDTH)) {
>> +			pr_err("Domain initialization failed\n");
>> +			domain_exit(dmar_domain);
>> +			return NULL;
>> +		}
>> +		domain_update_iommu_cap(dmar_domain);
>> +		domain = &dmar_domain->domain;
>> +		domain->geometry.aperture_start = 0;
>> +		domain->geometry.aperture_end   = __DOMAIN_MAX_ADDR(dmar_domain->gaw);
>> +		domain->geometry.force_aperture = true;
>> +		break;
>> +	case IOMMU_DOMAIN_DMA:
>> +		dmar_domain = alloc_domain(flags);
>> +		if (!dmar_domain) {
>> +			pr_err("Can't allocate dmar_domain\n");
> 
> Not necessary for memory allocation failure.

I’ll update in the next revision

> 
>> +			return NULL;
>> +		}
>> +		// init domain in device attach when we know IOMMU capabilities
> 
> Use /* */ for comments, please.

I’ll update in the next revision

> 
>> +		break;
>> +	case IOMMU_DOMAIN_IDENTITY:
>> +		flags |= DOMAIN_FLAG_STATIC_IDENTITY | DOMAIN_FLAG_INITIALISED;
>> +		dmar_domain = alloc_domain(flags);
>> +		if (!dmar_domain) {
>> +			pr_err("Can't allocate dmar_domain\n");
>> +			return NULL;
>> +		}
>> +		if (si_domain_init(dmar_domain, 0)) {
>> +			pr_err("Domain initialization failed\n");
>> +			domain_exit(dmar_domain);
>> +			return NULL;
>> +		}
>> +		break;
> 
> How about moving si domain allocation into a separated patch? There are
> two significant changes here, so it worth a new patch for discussion.
> 
> 1) a shared single si domain vs. per group si domain;
> 2) previously vt-d drivers determines what kind of devices should use
>   identity domain; Now, it turns to iommu generic layer, behavior will
>   be changed.

I’ll move it into another patch. Do you think the global si_domain should 
be returned here?

>> +	default:
>>  		return NULL;
>>  	}
>> -	domain_update_iommu_cap(dmar_domain);
>> -
>> -	domain = &dmar_domain->domain;
>> -	domain->geometry.aperture_start = 0;
>> -	domain->geometry.aperture_end   = __DOMAIN_MAX_ADDR(dmar_domain->gaw);
>> -	domain->geometry.force_aperture = true;
>>  -	return domain;
>> +	dmar_domain->domain.type = type;
> 
> Is it necessary to set this?

It isn’t I’ll remove this for the next revision.

> 
>> +	return &dmar_domain->domain;
>>  }
>>    static void intel_iommu_domain_free(struct iommu_domain *domain)
>> @@ -5080,8 +5129,8 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
>>  			dmar_remove_one_dev_info(old_domain, dev);
>>  			rcu_read_unlock();
>>  -			if (!domain_type_is_vm_or_si(old_domain) &&
>> -			     list_empty(&old_domain->devices))
>> +			if (list_empty(&old_domain->devices) &&
>> +			     !domain_managed_externally(old_domain))
>>  				domain_exit(old_domain);
>>  		}
>>  	}
>> @@ -5090,6 +5139,12 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
>>  	if (!iommu)
>>  		return -ENODEV;
>>  +	// Initialise domain with IOMMU capabilities if it isn't already initialised
> 
> Ditto.
> 
>> +	if (!domain_is_initialised(dmar_domain)) {
>> +		if (domain_init(dmar_domain, iommu, DEFAULT_DOMAIN_ADDRESS_WIDTH))
>> +			return -ENOMEM;
>> +	}
> 
> Each domain, not matter the DMA domain or UNMANAGED domain, is allocated
> first and then gets initialized during device attaching, right? If so,
> why do we need to have a special DOMAIN_FLAG_INITIALISED flag for DMA
> domains?

Only the DMA domain is initialised on attach, UNMANAGED and IDENTITY 
initialises with the lowest common denominator of the parameters of all 
attached IOMMUs using domain_update_iommu_cap.

> 
>> +
>>  	/* 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))
> 
> Best regards,
> Lu Baolu

Cheers,
James.