intel-iommu: errors with smaller iommu widths

When using iommu_domain_alloc with the Intel iommu, the domain address
width is always initialized to 48 bits (agaw 2).  This domain->agaw value
is then used by pfn_to_dma_pte to (always) build a 4 level page table.
However, not all systems support iommu width of 48 or 4 level page tables.
In particular, the Core i5-660 and i5-670 support an address width of 36
bits (not 39!), an agaw of only 1, and only 3 level page tables.

This version of the patch simply lops off extra levels of the page tables
if the agaw value of the iommu is less than what is currently allocated
for the domain (in intel_iommu_attach_device).  If there were already
allocated addresses above what the new iommu can handle, EFAULT is
returned.
Signed-off-by: Tom Lyon <pugs@cisco.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>

drivers/pci/intel-iommu.c

@@ -3433,19 +3433,6 @@ static void vm_domain_remove_all_dev_info(struct dmar_domain *domain)
 /* domain id for virtual machine, it won't be set in context */
 static unsigned long vm_domid;
 
-static int vm_domain_min_agaw(struct dmar_domain *domain)
-{
-	int i;
-	int min_agaw = domain->agaw;
-
-	for_each_set_bit(i, &domain->iommu_bmp, g_num_of_iommus) {
-		if (min_agaw > g_iommus[i]->agaw)
-			min_agaw = g_iommus[i]->agaw;
-	}
-
-	return min_agaw;
-}
-
 static struct dmar_domain *iommu_alloc_vm_domain(void)
 {
 	struct dmar_domain *domain;
@@ -3574,7 +3561,6 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
 	struct pci_dev *pdev = to_pci_dev(dev);
 	struct intel_iommu *iommu;
 	int addr_width;
-	u64 end;
 
 	/* normally pdev is not mapped */
 	if (unlikely(domain_context_mapped(pdev))) {
@@ -3597,14 +3583,30 @@ static int intel_iommu_attach_device(struct iommu_domain *domain,
 
 	/* check if this iommu agaw is sufficient for max mapped address */
 	addr_width = agaw_to_width(iommu->agaw);
-	end = DOMAIN_MAX_ADDR(addr_width);
-	end = end & VTD_PAGE_MASK;
-	if (end < dmar_domain->max_addr) {
-		printk(KERN_ERR "%s: iommu agaw (%d) is not "
+	if (addr_width > cap_mgaw(iommu->cap))
+		addr_width = cap_mgaw(iommu->cap);
+
+	if (dmar_domain->max_addr > (1LL << addr_width)) {
+		printk(KERN_ERR "%s: iommu width (%d) is not "
 		       "sufficient for the mapped address (%llx)\n",
-		       __func__, iommu->agaw, dmar_domain->max_addr);
+		       __func__, addr_width, dmar_domain->max_addr);
 		return -EFAULT;
 	}
+	dmar_domain->gaw = addr_width;
+
+	/*
+	 * Knock out extra levels of page tables if necessary
+	 */
+	while (iommu->agaw < dmar_domain->agaw) {
+		struct dma_pte *pte;
+
+		pte = dmar_domain->pgd;
+		if (dma_pte_present(pte)) {
+			free_pgtable_page(dmar_domain->pgd);
+			dmar_domain->pgd = (struct dma_pte *)dma_pte_addr(pte);
+		}
+		dmar_domain->agaw--;
+	}
 
 	return domain_add_dev_info(dmar_domain, pdev, CONTEXT_TT_MULTI_LEVEL);
 }