[PATCH v7 8/8] iommu/vt-d: Disallow read-only mappings to nest parent domain

[Yi Liu <yi.l.liu@intel.com>]

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  |  6 ++++++
 include/uapi/linux/iommufd.h | 12 +++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 85366862fb5e..1a50d3f53713 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2194,6 +2194,11 @@ __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->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) {
@@ -4872,6 +4877,7 @@ static void *intel_iommu_hw_info(struct device *dev, u32 *length, u32 *type)
 	if (!vtd)
 		return ERR_PTR(-ENOMEM);
 
+	vtd->flags = IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17;
 	vtd->cap_reg = iommu->cap;
 	vtd->ecap_reg = iommu->ecap;
 	*length = sizeof(*vtd);
diff --git a/include/uapi/linux/iommufd.h b/include/uapi/linux/iommufd.h
index 3a66d3888393..cb7d17e3b4e7 100644
--- a/include/uapi/linux/iommufd.h
+++ b/include/uapi/linux/iommufd.h
@@ -444,10 +444,20 @@ struct iommu_hwpt_alloc {
 };
 #define IOMMU_HWPT_ALLOC _IO(IOMMUFD_TYPE, IOMMUFD_CMD_HWPT_ALLOC)
 
+/**
+ * enum iommu_hw_info_vtd_flags - Flags for VT-d hw_info
+ * @IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17: If set, disallow nesting on domains
+ *                                   with read-only mapping.
+ *                                   https://www.intel.com/content/www/us/en/content-details/772415/content-details.html
+ */
+enum iommu_hw_info_vtd_flags {
+	IOMMU_HW_INFO_VTD_ERRATA_772415_SPR17 = 1 << 0,
+};
+
 /**
  * struct iommu_hw_info_vtd - Intel VT-d hardware information
  *
- * @flags: Must be 0
+ * @flags: Combination of enum iommu_hw_info_vtd_flags
  * @__reserved: Must be 0
  *
  * @cap_reg: Value of Intel VT-d capability register defined in VT-d spec
-- 
2.34.1