RE: [PATCH v2 3/3] iommu/vt-d: Use second level for GPA->HPA translation

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> Sent: Sunday, September 26, 2021 7:46 PM
> 
> 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're different in some way. For example, the second
> level translation has separate controls for the Access/Dirty page tracking.
> With the first level translation, there's no such control. On the other
> hand, the second level translation has the page-level control for forcing
> snoop, but the first level only has global control with pasid granularity.
> 
> This uses the second level for GPA->HPA translation so that we can provide
> a consistent hardware interface for use cases like dirty page tracking for
> live migration.
> 
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>  drivers/iommu/intel/iommu.c | 12 +++++++++---
>  1 file changed, 9 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index dc2030d014e0..426630261614 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -1991,9 +1991,15 @@ 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();

/* Only SL is available in legacy mode */

> +	if (!scalable_mode_support())
> +		return false;
> +

/* if only level (either FL or SL) is available, just use it */

> +	if (intel_cap_flts_sanity() ^ intel_cap_slts_sanity())
> +		return intel_cap_flts_sanity();
> +

/* if both levels are available, decide it based on domain type */

> +	return type != IOMMU_DOMAIN_UNMANAGED;
>  }

with above comments added:

Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>

> 
>  static struct dmar_domain *alloc_domain(unsigned int type)
> @@ -2006,7 +2012,7 @@ static struct dmar_domain
> *alloc_domain(unsigned int type)
> 
>  	memset(domain, 0, sizeof(*domain));
>  	domain->nid = NUMA_NO_NODE;
> -	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);
> --
> 2.25.1