tests: replace mmap with test kernel module for test_read_physical()

tests.linux_kernel.helpers.test_mm.TestMm.test_read_physical() fails on
Arm when the user page is mapped from high memory. Replace it with a
test case that uses the test physical address from the test kernel
module and asserts the expected PRNG data. (We will probably run into
more tests that fail with high memory once #244 is merged.)

Signed-off-by: Omar Sandoval <[email protected]>

Author: osandov

tests/linux_kernel/helpers/test_mm.py

@@ -6,6 +6,7 @@
 import mmap
 import os
 import struct
+import sys
 import tempfile
 import unittest
 
@@ -43,6 +44,7 @@
 from tests.linux_kernel import (
     LinuxKernelTestCase,
     mlock,
+    prng32,
     skip_unless_have_full_mm_support,
     skip_unless_have_test_kmod,
 )
@@ -227,13 +229,16 @@ def test_virt_to_phys(self):
             virt_to_phys(self.prog["drgn_test_va"]), self.prog["drgn_test_pa"]
         )
 
+    @skip_unless_have_test_kmod
     def test_read_physical(self):
-        with self._pages() as (map, _, pfns):
-            for i, pfn in enumerate(pfns):
-                self.assertEqual(
-                    self.prog.read(pfn * mmap.PAGESIZE, mmap.PAGESIZE, True),
-                    map[i * mmap.PAGESIZE : (i + 1) * mmap.PAGESIZE],
-                )
+        expected = bytearray()
+        for x in prng32("PAGE"):
+            expected.extend(x.to_bytes(4, sys.byteorder))
+            if len(expected) >= mmap.PAGESIZE:
+                break
+        self.assertEqual(
+            self.prog.read(self.prog["drgn_test_pa"], mmap.PAGESIZE, True), expected
+        )
 
     @skip_unless_have_full_mm_support
     def test_access_process_vm(self):

tests/linux_kernel/kmod/drgn_test.c

@@ -150,13 +150,21 @@ struct page *drgn_test_compound_page;
 
 static int drgn_test_mm_init(void)
 {
+	u32 fill;
+
 	drgn_test_page = alloc_page(GFP_KERNEL);
 	if (!drgn_test_page)
 		return -ENOMEM;
 	drgn_test_compound_page = alloc_pages(GFP_KERNEL | __GFP_COMP, 1);
 	if (!drgn_test_compound_page)
 		return -ENOMEM;
 	drgn_test_va = page_address(drgn_test_page);
+	// Fill the page with a PRNG sequence.
+	fill = drgn_test_prng32_seed("PAGE");
+	for (int i = 0; i < PAGE_SIZE / sizeof(fill); i++) {
+		fill = drgn_test_prng32(fill);
+		((u32 *)drgn_test_va)[i] = fill;
+	}
 	drgn_test_pa = virt_to_phys(drgn_test_va);
 	drgn_test_pfn = PHYS_PFN(drgn_test_pa);
 	return 0;