iommu/vt-d: Check if domain->pgd was allocated

There is a couple of places where on domain_init() failure domain_exit()
is called. While currently domain_init() can fail only if
alloc_pgtable_page() has failed.

Make domain_exit() check if domain->pgd present, before calling
domain_unmap(), as it theoretically should crash on clearing pte entries
in dma_pte_clear_level().

Cc: David Woodhouse <dwmw2@infradead.org>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Lu Baolu <baolu.lu@linux.intel.com>
Cc: iommu@lists.linux-foundation.org
Signed-off-by: Dmitry Safonov <dima@arista.com>
Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/intel-iommu.c

@@ -1890,7 +1890,6 @@ static int domain_init(struct dmar_domain *domain, struct intel_iommu *iommu,
 
 static void domain_exit(struct dmar_domain *domain)
 {
-	struct page *freelist;
 
 	/* Remove associated devices and clear attached or cached domains */
 	domain_remove_dev_info(domain);
@@ -1898,9 +1897,12 @@ static void domain_exit(struct dmar_domain *domain)
 	/* destroy iovas */
 	put_iova_domain(&domain->iovad);
 
-	freelist = domain_unmap(domain, 0, DOMAIN_MAX_PFN(domain->gaw));
+	if (domain->pgd) {
+		struct page *freelist;
 
-	dma_free_pagelist(freelist);
+		freelist = domain_unmap(domain, 0, DOMAIN_MAX_PFN(domain->gaw));
+		dma_free_pagelist(freelist);
+	}
 
 	free_domain_mem(domain);
 }