Re: [PATCH v6 8/8] iommu/vt-d: Disallow read-only mappings to nest parent domain

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

On 10/20/23 5:32 PM, Yi Liu wrote:
> From: Lu Baolu <baolu.lu@linux.intel.com>
> 
> When remapping hardware is configured by system software in scalable mode
> as Nested (PGTT=011b) and with PWSNP field Set in the PASID-table-entry,
> it may Set Accessed bit and Dirty bit (and Extended Access bit if enabled)
> in first-stage page-table entries even when second-stage mappings indicate
> that corresponding first-stage page-table is Read-Only.
> 
> As the result, contents of pages designated by VMM as Read-Only can be
> modified by IOMMU via PML5E (PML4E for 4-level tables) access as part of
> address translation process due to DMAs issued by Guest.
> 
> This disallows read-only mappings in the domain that is supposed to be used
> as nested parent. Reference from Sapphire Rapids Specification Update [1],
> errata details, SPR17. Userspace should know this limitation by checking
> the IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 flag reported in the IOMMU_GET_HW_INFO
> ioctl.
> 
> [1] https://www.intel.com/content/www/us/en/content-details/772415/content-details.html
> 
> Reviewed-by: Kevin Tian <kevin.tian@intel.com>
> Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
> Signed-off-by: Yi Liu <yi.l.liu@intel.com>
> ---
>   drivers/iommu/intel/iommu.c  |  9 +++++++++
>   drivers/iommu/intel/iommu.h  |  1 +
>   include/uapi/linux/iommufd.h | 12 +++++++++++-
>   3 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index c7704e7efd4a..a0341a069fbf 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2193,6 +2193,11 @@ __domain_mapping(struct dmar_domain *domain, unsigned long iov_pfn,
>   	if ((prot & (DMA_PTE_READ|DMA_PTE_WRITE)) == 0)
>   		return -EINVAL;
>   
> +	if (!(prot & DMA_PTE_WRITE) && domain->is_nested_parent) {
> +		pr_err_ratelimited("Read-only mapping is disallowed on the domain which serves as the parent in a nested configuration, due to HW errata (ERRATA_772415_SPR17)\n");
> +		return -EINVAL;
> +	}
> +
>   	attr = prot & (DMA_PTE_READ | DMA_PTE_WRITE | DMA_PTE_SNP);
>   	attr |= DMA_FL_PTE_PRESENT;
>   	if (domain->use_first_level) {
> @@ -4101,6 +4106,9 @@ intel_iommu_domain_alloc_user(struct device *dev, u32 flags,
>   		domain = iommu_domain_alloc(dev->bus);
>   		if (!domain)
>   			return ERR_PTR(-ENOMEM);
> +		container_of(domain,
> +			     struct dmar_domain,
> +			     domain)->is_nested_parent = request_nest_parent;

How about
		to_dmar_domain(domain)->is_nested_parent = ...;
?

I would also prefer to introduce is_nested_parent_domain to the user
domain allocation patch (patch 7/8). This field should be checked when
allocating a nested user domain.

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 8f81a5c9fcc0..d3f6bc1f6590 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4121,6 +4121,8 @@ intel_iommu_domain_alloc_user(struct device *dev, 
u32 flags,
                 return ERR_PTR(-EINVAL);
         if (request_nest_parent)
                 return ERR_PTR(-EINVAL);
+       if (!to_dmar_domain(parent)->is_nested_parent)
+               return ERR_PTR(-EINVAL);

         return intel_nested_domain_alloc(parent, user_data);
  }

Best regards,
baolu