+ selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem.patch added to mm-new branch

+ selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem.patch added to mm-new branch

[Andrew Morton]

The patch titled
     Subject: selftests/mm: add simple VM_PFNMAP tests based on mmap'ing /dev/mem
has been added to the -mm mm-new branch.  Its filename is
     selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem.patch

This patch will later appear in the mm-new branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

Note, mm-new is a provisional staging ground for work-in-progress
patches, and acceptance into mm-new is a notification for others take
notice and to finish up reviews.  Please do not hesitate to respond to
review feedback and post updated versions to replace or incrementally
fixup patches in mm-new.

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*** Remember to use Documentation/process/submit-checklist.rst when testing your code ***

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branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
and is updated there every 2-3 working days

------------------------------------------------------
From: David Hildenbrand <david@redhat.com>
Subject: selftests/mm: add simple VM_PFNMAP tests based on mmap'ing /dev/mem
Date: Fri, 9 May 2025 17:30:32 +0200

Let's test some basic functionality using /dev/mem.  These tests will
implicitly cover some PAT (Page Attribute Handling) handling on x86.

These tests will only run when /dev/mem access to the first two pages in
physical address space is possible and allowed; otherwise, the tests are
skipped.

On current x86-64 with PAT inside a VM, all tests pass:

	TAP version 13
	1..6
	# Starting 6 tests from 1 test cases.
	#  RUN           pfnmap.madvise_disallowed ...
	#            OK  pfnmap.madvise_disallowed
	ok 1 pfnmap.madvise_disallowed
	#  RUN           pfnmap.munmap_split ...
	#            OK  pfnmap.munmap_split
	ok 2 pfnmap.munmap_split
	#  RUN           pfnmap.mremap_fixed ...
	#            OK  pfnmap.mremap_fixed
	ok 3 pfnmap.mremap_fixed
	#  RUN           pfnmap.mremap_shrink ...
	#            OK  pfnmap.mremap_shrink
	ok 4 pfnmap.mremap_shrink
	#  RUN           pfnmap.mremap_expand ...
	#            OK  pfnmap.mremap_expand
	ok 5 pfnmap.mremap_expand
	#  RUN           pfnmap.fork ...
	#            OK  pfnmap.fork
	ok 6 pfnmap.fork
	# PASSED: 6 / 6 tests passed.
	# Totals: pass:6 fail:0 xfail:0 xpass:0 skip:0 error:0

However, we are able to trigger:

[   27.888251] x86/PAT: pfnmap:1790 freeing invalid memtype [mem 0x00000000-0x00000fff]

There are probably more things worth testing in the future, such as
MAP_PRIVATE handling.  But this set of tests is sufficient to cover most
of the things we will rework regarding PAT handling.

Link: https://lkml.kernel.org/r/20250509153033.952746-1-david@redhat.com
Signed-off-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Peter Xu <peterx@redhat.com>
Cc: Dev Jain <dev.jain@arm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 tools/testing/selftests/mm/.gitignore     |    1 
 tools/testing/selftests/mm/Makefile       |    1 
 tools/testing/selftests/mm/pfnmap.c       |  196 ++++++++++++++++++++
 tools/testing/selftests/mm/run_vmtests.sh |    4 
 4 files changed, 202 insertions(+)

--- a/tools/testing/selftests/mm/.gitignore~selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem
+++ a/tools/testing/selftests/mm/.gitignore
@@ -20,6 +20,7 @@ mremap_test
 on-fault-limit
 transhuge-stress
 pagemap_ioctl
+pfnmap
 *.tmp*
 protection_keys
 protection_keys_32
--- a/tools/testing/selftests/mm/Makefile~selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem
+++ a/tools/testing/selftests/mm/Makefile
@@ -84,6 +84,7 @@ TEST_GEN_FILES += mremap_test
 TEST_GEN_FILES += mseal_test
 TEST_GEN_FILES += on-fault-limit
 TEST_GEN_FILES += pagemap_ioctl
+TEST_GEN_FILES += pfnmap
 TEST_GEN_FILES += thuge-gen
 TEST_GEN_FILES += transhuge-stress
 TEST_GEN_FILES += uffd-stress
diff --git a/tools/testing/selftests/mm/pfnmap.c a/tools/testing/selftests/mm/pfnmap.c
new file mode 100644
--- /dev/null
+++ a/tools/testing/selftests/mm/pfnmap.c
@@ -0,0 +1,196 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Basic VM_PFNMAP tests relying on mmap() of '/dev/mem'
+ *
+ * Copyright 2025, Red Hat, Inc.
+ *
+ * Author(s): David Hildenbrand <david@redhat.com>
+ */
+#define _GNU_SOURCE
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <unistd.h>
+#include <errno.h>
+#include <fcntl.h>
+#include <signal.h>
+#include <setjmp.h>
+#include <linux/mman.h>
+#include <sys/mman.h>
+#include <sys/wait.h>
+
+#include "../kselftest_harness.h"
+#include "vm_util.h"
+
+static sigjmp_buf sigjmp_buf_env;
+
+static void signal_handler(int sig)
+{
+	siglongjmp(sigjmp_buf_env, -EFAULT);
+}
+
+static int test_read_access(char *addr, size_t size, size_t pagesize)
+{
+	size_t offs;
+	int ret;
+
+	if (signal(SIGSEGV, signal_handler) == SIG_ERR)
+		return -EINVAL;
+
+	ret = sigsetjmp(sigjmp_buf_env, 1);
+	if (!ret) {
+		for (offs = 0; offs < size; offs += pagesize)
+			/* Force a read that the compiler cannot optimize out. */
+			*((volatile char *)(addr + offs));
+	}
+	if (signal(SIGSEGV, signal_handler) == SIG_ERR)
+		return -EINVAL;
+
+	return ret;
+}
+
+FIXTURE(pfnmap)
+{
+	size_t pagesize;
+	int dev_mem_fd;
+	char *addr1;
+	size_t size1;
+	char *addr2;
+	size_t size2;
+};
+
+FIXTURE_SETUP(pfnmap)
+{
+	self->pagesize = getpagesize();
+
+	self->dev_mem_fd = open("/dev/mem", O_RDONLY);
+	if (self->dev_mem_fd < 0)
+		SKIP(return, "Cannot open '/dev/mem'\n");
+
+	/* We'll require the first two pages throughout our tests ... */
+	self->size1 = self->pagesize * 2;
+	self->addr1 = mmap(NULL, self->size1, PROT_READ, MAP_SHARED,
+			   self->dev_mem_fd, 0);
+	if (self->addr1 == MAP_FAILED)
+		SKIP(return, "Cannot mmap '/dev/mem'\n");
+
+	/* ... and want to be able to read from them. */
+	if (test_read_access(self->addr1, self->size1, self->pagesize))
+		SKIP(return, "Cannot read-access mmap'ed '/dev/mem'\n");
+
+	self->size2 = 0;
+	self->addr2 = MAP_FAILED;
+}
+
+FIXTURE_TEARDOWN(pfnmap)
+{
+	if (self->addr2 != MAP_FAILED)
+		munmap(self->addr2, self->size2);
+	if (self->addr1 != MAP_FAILED)
+		munmap(self->addr1, self->size1);
+	if (self->dev_mem_fd >= 0)
+		close(self->dev_mem_fd);
+}
+
+TEST_F(pfnmap, madvise_disallowed)
+{
+	int advices[] = {
+		MADV_DONTNEED,
+		MADV_DONTNEED_LOCKED,
+		MADV_FREE,
+		MADV_WIPEONFORK,
+		MADV_COLD,
+		MADV_PAGEOUT,
+		MADV_POPULATE_READ,
+		MADV_POPULATE_WRITE,
+	};
+	int i;
+
+	/* All these advices must be rejected. */
+	for (i = 0; i < ARRAY_SIZE(advices); i++) {
+		EXPECT_LT(madvise(self->addr1, self->pagesize, advices[i]), 0);
+		EXPECT_EQ(errno, EINVAL);
+	}
+}
+
+TEST_F(pfnmap, munmap_split)
+{
+	/*
+	 * Unmap the first page. This munmap() call is not really expected to
+	 * fail, but we might be able to trigger other internal issues.
+	 */
+	ASSERT_EQ(munmap(self->addr1, self->pagesize), 0);
+
+	/*
+	 * Remap the first page while the second page is still mapped. This
+	 * makes sure that any PAT tracking on x86 will allow for mmap()'ing
+	 * a page again while some parts of the first mmap() are still
+	 * around.
+	 */
+	self->size2 = self->pagesize;
+	self->addr2 = mmap(NULL, self->pagesize, PROT_READ, MAP_SHARED,
+			   self->dev_mem_fd, 0);
+	ASSERT_NE(self->addr2, MAP_FAILED);
+}
+
+TEST_F(pfnmap, mremap_fixed)
+{
+	char *ret;
+
+	/* Reserve a destination area. */
+	self->size2 = self->size1;
+	self->addr2 = mmap(NULL, self->size2, PROT_READ, MAP_ANON | MAP_PRIVATE,
+			   -1, 0);
+	ASSERT_NE(self->addr2, MAP_FAILED);
+
+	/* mremap() over our destination. */
+	ret = mremap(self->addr1, self->size1, self->size2,
+		     MREMAP_FIXED | MREMAP_MAYMOVE, self->addr2);
+	ASSERT_NE(ret, MAP_FAILED);
+}
+
+TEST_F(pfnmap, mremap_shrink)
+{
+	char *ret;
+
+	/* Shrinking is expected to work. */
+	ret = mremap(self->addr1, self->size1, self->size1 - self->pagesize, 0);
+	ASSERT_NE(ret, MAP_FAILED);
+}
+
+TEST_F(pfnmap, mremap_expand)
+{
+	/*
+	 * Growing is not expected to work, and getting it right would
+	 * be challenging. So this test primarily serves as an early warning
+	 * that something that probably should never work suddenly works.
+	 */
+	self->size2 = self->size1 + self->pagesize;
+	self->addr2 = mremap(self->addr1, self->size1, self->size2, MREMAP_MAYMOVE);
+	ASSERT_EQ(self->addr2, MAP_FAILED);
+}
+
+TEST_F(pfnmap, fork)
+{
+	pid_t pid;
+	int ret;
+
+	/* fork() a child and test if the child can access the pages. */
+	pid = fork();
+	ASSERT_GE(pid, 0);
+
+	if (!pid) {
+		EXPECT_EQ(test_read_access(self->addr1, self->size1,
+					   self->pagesize), 0);
+		exit(0);
+	}
+
+	wait(&ret);
+	if (WIFEXITED(ret))
+		ret = WEXITSTATUS(ret);
+	else
+		ret = -EINVAL;
+	ASSERT_EQ(ret, 0);
+}
+
+TEST_HARNESS_MAIN
--- a/tools/testing/selftests/mm/run_vmtests.sh~selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem
+++ a/tools/testing/selftests/mm/run_vmtests.sh
@@ -63,6 +63,8 @@ separated by spaces:
 	test soft dirty page bit semantics
 - pagemap
 	test pagemap_scan IOCTL
+- pfnmap
+	tests for VM_PFNMAP handling
 - cow
 	test copy-on-write semantics
 - thp
@@ -472,6 +474,8 @@ fi
 
 CATEGORY="pagemap" run_test ./pagemap_ioctl
 
+CATEGORY="pfnmap" run_test ./pfnmap
+
 # COW tests
 CATEGORY="cow" run_test ./cow
 
_

Patches currently in -mm which might be from david@redhat.com are

kernel-fork-only-call-untrack_pfn_clear-on-vmas-duplicated-for-fork.patch
kernel-events-uprobes-pass-vma-instead-of-mm-to-remove_breakpoint.patch
kernel-events-uprobes-pass-vma-to-set_swbp-set_orig_insn-and-uprobe_write_opcode.patch
kernel-events-uprobes-uprobe_write_opcode-rewrite.patch
selftests-mm-add-simple-vm_pfnmap-tests-based-on-mmaping-dev-mem.patch