kernel: vm: Add vm_zero_page() helper

Signed-off-by: sigsegv7 <ian@vegaa.systems>

1 files changed, 73 insertions, 0 deletions

diff --git a/sys/vm/vm_page.c b/sys/vm/vm_page.c
new file mode 100644
index 0000000..d344f4b
--- /dev/null
+++ b/sys/vm/vm_page.c
@@ -0,0 +1,73 @@
+/*
+ * Copyright (c) 2023 Ian Marco Moffett and the VegaOS team.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. Neither the name of VegaOS nor the names of its
+ *    contributors may be used to endorse or promote products derived from
+ *    this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/cdefs.h>
+#include <sys/panic.h>
+#include <vm/vm_page.h>
+#include <vm/vm.h>
+#include <string.h>
+
+__MODULE_NAME("vm_page");
+__KERNEL_META("$Vega$: vm_page.c, Ian Marco Moffett, "
+              "Virtual memory page specific operations");
+
+/*
+ * Zero `page_count' pages.
+ *
+ * @page: First page to start zeroing at
+ * @page_count: Number of pages to zero.
+ */
+void
+vm_zero_page(void *page, size_t page_count)
+{
+    const size_t PAGE_SIZE = vm_get_page_size();
+    size_t bytes = page_count * PAGE_SIZE;
+
+    /*
+     * This *should not* happen. Page sizes
+     * are usually 2^n but if this runs, something
+     * *very* weird is happening and either something
+     * broke badly. Or it's that damn technological
+     * degeneration that is getting out of hand within
+     * our world!! But really, page sizes *should* be a
+     * power of 2 and it would be pretty worrying if
+     * this branches causing a panic stating something
+     * that shouldn't happen, happened.
+     *
+     * The reason why it is wise for pages to be a power of
+     * 2 is so we can efficiently read/write to the page in
+     * fixed-sized power of 2 blocks cleanly without the risk
+     * of clobbering other pages we didn't intend to mess with.
+     */
+    if ((PAGE_SIZE & 1) != 0) {
+        panic("Unexpected page size, not power of 2!\n");
+    }
+
+    memset64(page, 0, bytes/8);
+}