RE: [PATCH 1/1] iommu/vt-d: Use second level for GPA->HPA translation

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Friday, September 24, 2021 10:30 AM
> 
> The IOMMU VT-d implementation uses the first level for GPA->HPA
> translation
> by default. Although both the first level and the second level could handle
> the DMA translation, they are different in some way. For example, the
> second
> level translation has separate controls for the Access/Dirty page tracking
> and the page-level forcing snoop. With first level translation, there're
> no such controls. This uses the second level for GPA->HPA translation so

first-level has no page-granular snoop control, but has a global control
in pasid entry.

> that it could provide a consistent hardware interface for use cases like
> dirty page tracking during the VM live migration.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  include/linux/intel-iommu.h |  7 ++-----
>  drivers/iommu/intel/iommu.c | 21 +++++++++++++--------
>  2 files changed, 15 insertions(+), 13 deletions(-)
> 
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index 05a65eb155f7..a5fb20702201 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -517,22 +517,19 @@ struct context_entry {
>  	u64 hi;
>  };
> 
> -/* si_domain contains mulitple devices */
> -#define DOMAIN_FLAG_STATIC_IDENTITY		BIT(0)

this is a separate cleanup. better mention it in the commit msg or
put in another patch.

> -
>  /*
>   * When VT-d works in the scalable mode, it allows DMA translation to
>   * happen through either first level or second level page table. This
>   * bit marks that the DMA translation for the domain goes through the
>   * first level page table, otherwise, it goes through the second level.
>   */
> -#define DOMAIN_FLAG_USE_FIRST_LEVEL		BIT(1)
> +#define DOMAIN_FLAG_USE_FIRST_LEVEL		BIT(0)
> 
>  /*
>   * Domain represents a virtual machine which demands iommu nested
>   * translation mode support.
>   */
> -#define DOMAIN_FLAG_NESTING_MODE		BIT(2)
> +#define DOMAIN_FLAG_NESTING_MODE		BIT(1)
> 
>  struct dmar_domain {
>  	int	nid;			/* node id */
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index d75f59ae28e6..c814fea0522e 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -522,7 +522,7 @@ static inline void free_devinfo_mem(void *vaddr)
> 
>  static inline int domain_type_is_si(struct dmar_domain *domain)
>  {
> -	return domain->flags & DOMAIN_FLAG_STATIC_IDENTITY;
> +	return domain->domain.type == IOMMU_DOMAIN_IDENTITY;
>  }
> 
>  static inline bool domain_use_first_level(struct dmar_domain *domain)
> @@ -1874,12 +1874,18 @@ static void free_dmar_iommu(struct
> intel_iommu *iommu)
>   * Check and return whether first level is used by default for
>   * DMA translation.
>   */
> -static bool first_level_by_default(void)
> +static bool first_level_by_default(unsigned int type)
>  {
> -	return scalable_mode_support() && intel_cap_flts_sanity();
> +	if (type == IOMMU_DOMAIN_UNMANAGED)
> +		return false;
> +

I think the order is not correct. what about 2nd level is even not
present?


> +	if (!scalable_mode_support() || !intel_cap_flts_sanity())
> +		return false;
> +
> +	return true;
>  }
> 
> -static struct dmar_domain *alloc_domain(int flags)
> +static struct dmar_domain *alloc_domain(unsigned int type)
>  {
>  	struct dmar_domain *domain;
> 
> @@ -1889,8 +1895,7 @@ static struct dmar_domain *alloc_domain(int flags)
> 
>  	memset(domain, 0, sizeof(*domain));
>  	domain->nid = NUMA_NO_NODE;
> -	domain->flags = flags;
> -	if (first_level_by_default())
> +	if (first_level_by_default(type))
>  		domain->flags |= DOMAIN_FLAG_USE_FIRST_LEVEL;
>  	domain->has_iotlb_device = false;
>  	INIT_LIST_HEAD(&domain->devices);
> @@ -2708,7 +2713,7 @@ static int __init si_domain_init(int hw)
>  	struct device *dev;
>  	int i, nid, ret;
> 
> -	si_domain = alloc_domain(DOMAIN_FLAG_STATIC_IDENTITY);
> +	si_domain = alloc_domain(IOMMU_DOMAIN_IDENTITY);
>  	if (!si_domain)
>  		return -EFAULT;
> 
> @@ -4517,7 +4522,7 @@ static struct iommu_domain
> *intel_iommu_domain_alloc(unsigned type)
>  	case IOMMU_DOMAIN_DMA:
>  	case IOMMU_DOMAIN_DMA_FQ:
>  	case IOMMU_DOMAIN_UNMANAGED:
> -		dmar_domain = alloc_domain(0);
> +		dmar_domain = alloc_domain(type);
>  		if (!dmar_domain) {
>  			pr_err("Can't allocate dmar_domain\n");
>  			return NULL;
> --
> 2.25.1