--- /dev/null
+// 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
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