iommu/vt-d: Flush cache for PASID table before using it

When writing the address of a freshly allocated zero-initialized PASID
table to a PASID directory entry, do that after the CPU cache flush for
this PASID table, not before it, to avoid the time window when this
PASID table may be already used by non-coherent IOMMU hardware while
its contents in RAM is still some random old data, not zero-initialized.

Fixes: 194b334 ("iommu/vt-d: Fix PASID directory pointer coherency")
Signed-off-by: Dmytro Maluka <dmaluka@chromium.org>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20251221123508.37495-1-dmaluka@chromium.org
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

Author: maluka-dmytro

drivers/iommu/intel/pasid.c

@@ -153,6 +153,9 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
 		if (!entries)
 			return NULL;
 
+		if (!ecap_coherent(info->iommu->ecap))
+			clflush_cache_range(entries, VTD_PAGE_SIZE);
+
 		/*
 		 * The pasid directory table entry won't be freed after
 		 * allocation. No worry about the race with free and
@@ -165,10 +168,8 @@ static struct pasid_entry *intel_pasid_get_entry(struct device *dev, u32 pasid)
 			iommu_free_pages(entries);
 			goto retry;
 		}
-		if (!ecap_coherent(info->iommu->ecap)) {
-			clflush_cache_range(entries, VTD_PAGE_SIZE);
+		if (!ecap_coherent(info->iommu->ecap))
 			clflush_cache_range(&dir[dir_index].val, sizeof(*dir));
-		}
 	}
 
 	return &entries[index];