[xen staging] VT-d: limit page table population in domain_pgd_maddr()

[patchbot@xxxxxxx]

commit 4e977a70adb1b9036d5fa7705d73ab5dd087faa4
Author:     Jan Beulich <jbeulich@xxxxxxxx>
AuthorDate: Fri Apr 22 14:53:13 2022 +0200
Commit:     Jan Beulich <jbeulich@xxxxxxxx>
CommitDate: Fri Apr 22 14:53:13 2022 +0200

    VT-d: limit page table population in domain_pgd_maddr()
    
    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>
    Reviewed-by: Kevin Tian <kevin.tian@xxxxxxxxx>
---
 xen/drivers/passthrough/vtd/iommu.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/xen/drivers/passthrough/vtd/iommu.c 
b/xen/drivers/passthrough/vtd/iommu.c
index 4400f56459..f68d960d75 100644
--- a/xen/drivers/passthrough/vtd/iommu.c
+++ b/xen/drivers/passthrough/vtd/iommu.c
@@ -61,6 +61,7 @@ bool __read_mostly iommu_snoop = true;
 #endif
 
 static unsigned int __read_mostly nr_iommus;
+static unsigned int __ro_after_init min_pt_levels = UINT_MAX;
 
 static struct tasklet vtd_fault_tasklet;
 
@@ -439,8 +440,11 @@ static paddr_t domain_pgd_maddr(struct domain *d, paddr_t 
pgd_maddr,
     {
         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;
@@ -1349,6 +1353,8 @@ int __init iommu_alloc(struct acpi_drhd_unit *drhd)
         goto free;
     }
     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) )
         iommu_non_coherent = true;
--
generated by git-patchbot for /home/xen/git/xen.git#staging