Merge tag 'for-linus-urgent' of git://git.kernel.org/pub/scm/virt/kvm/kvm

Pull kvm fixes from Paolo Bonzini:
 "A selftests fix for ARM, and the fix for page reference count
  underflow. This is a very small fix that was provided by Nick Piggin
  and tested by myself"

* tag 'for-linus-urgent' of git://git.kernel.org/pub/scm/virt/kvm/kvm:
  KVM: do not allow mapping valid but non-reference-counted pages
  KVM: selftests: Fix mapping length truncation in m{,un}map()

tools/testing/selftests/kvm/set_memory_region_test.c

@@ -376,7 +376,7 @@ static void test_add_max_memory_regions(void)
 	pr_info("Adding slots 0..%i, each memory region with %dK size\n",
 		(max_mem_slots - 1), MEM_REGION_SIZE >> 10);
 
-	mem = mmap(NULL, MEM_REGION_SIZE * max_mem_slots + alignment,
+	mem = mmap(NULL, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment,
 		   PROT_READ | PROT_WRITE, MAP_PRIVATE | MAP_ANONYMOUS, -1, 0);
 	TEST_ASSERT(mem != MAP_FAILED, "Failed to mmap() host");
 	mem_aligned = (void *)(((size_t) mem + alignment - 1) & ~(alignment - 1));
@@ -401,7 +401,7 @@ static void test_add_max_memory_regions(void)
 	TEST_ASSERT(ret == -1 && errno == EINVAL,
 		    "Adding one more memory slot should fail with EINVAL");
 
-	munmap(mem, MEM_REGION_SIZE * max_mem_slots + alignment);
+	munmap(mem, (size_t)max_mem_slots * MEM_REGION_SIZE + alignment);
 	munmap(mem_extra, MEM_REGION_SIZE);
 	kvm_vm_free(vm);
 }

virt/kvm/kvm_main.c

@@ -2055,6 +2055,13 @@ static bool vma_is_valid(struct vm_area_struct *vma, bool write_fault)
 	return true;
 }
 
+static int kvm_try_get_pfn(kvm_pfn_t pfn)
+{
+	if (kvm_is_reserved_pfn(pfn))
+		return 1;
+	return get_page_unless_zero(pfn_to_page(pfn));
+}
+
 static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 			       unsigned long addr, bool *async,
 			       bool write_fault, bool *writable,
@@ -2104,13 +2111,21 @@ static int hva_to_pfn_remapped(struct vm_area_struct *vma,
 	 * Whoever called remap_pfn_range is also going to call e.g.
 	 * unmap_mapping_range before the underlying pages are freed,
 	 * causing a call to our MMU notifier.
+	 *
+	 * Certain IO or PFNMAP mappings can be backed with valid
+	 * struct pages, but be allocated without refcounting e.g.,
+	 * tail pages of non-compound higher order allocations, which
+	 * would then underflow the refcount when the caller does the
+	 * required put_page. Don't allow those pages here.
 	 */ 
-	kvm_get_pfn(pfn);
+	if (!kvm_try_get_pfn(pfn))
+		r = -EFAULT;
 
 out:
 	pte_unmap_unlock(ptep, ptl);
 	*p_pfn = pfn;
-	return 0;
+
+	return r;
 }
 
 /*