[PATCH v3 03/23] VT-d: limit page table population in domain_pgd_maddr()

[Jan Beulich <jbeulich@xxxxxxxx>]

I have to admit that I never understood why domain_pgd_maddr() wants to
populate all page table levels for DFN 0. I can only assume that despite
the comment there what is needed is population just down to the smallest
possible nr_pt_levels that the loop later in the function may need to
run to. Hence what is needed is the minimum of all possible
iommu->nr_pt_levels, to then be passed into addr_to_dma_page_maddr()
instead of literal 1.

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxx>
---
v3: New.

--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -55,6 +55,7 @@ bool __read_mostly iommu_snoop = true;
 #endif
 
 static unsigned int __read_mostly nr_iommus;
+static unsigned int __read_mostly min_pt_levels = UINT_MAX;
 
 static struct iommu_ops vtd_ops;
 static struct tasklet vtd_fault_tasklet;
@@ -482,8 +483,11 @@ static uint64_t domain_pgd_maddr(struct
     {
         if ( !hd->arch.vtd.pgd_maddr )
         {
-            /* Ensure we have pagetables allocated down to leaf PTE. */
-            addr_to_dma_page_maddr(d, 0, 1, NULL, true);
+            /*
+             * Ensure we have pagetables allocated down to the smallest
+             * level the loop below may need to run to.
+             */
+            addr_to_dma_page_maddr(d, 0, min_pt_levels, NULL, true);
 
             if ( !hd->arch.vtd.pgd_maddr )
                 return 0;
@@ -1381,6 +1385,8 @@ int __init iommu_alloc(struct acpi_drhd_
         return -ENODEV;
     }
     iommu->nr_pt_levels = agaw_to_level(agaw);
+    if ( min_pt_levels > iommu->nr_pt_levels )
+        min_pt_levels = iommu->nr_pt_levels;
 
     if ( !ecap_coherent(iommu->ecap) )
         vtd_ops.sync_cache = sync_cache;