kern/amd64+mu: Add initial virtual memory sources

Signed-off-by: Ian Moffett <ian@osmora.org>

1 files changed, 98 insertions, 0 deletions

diff --git a/sys/arch/amd64/cpu/mmu.c b/sys/arch/amd64/cpu/mmu.c
new file mode 100644
index 0000000..65c4e46
--- /dev/null
+++ b/sys/arch/amd64/cpu/mmu.c
@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2023-2025 Ian Marco Moffett and the Osmora 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 Hyra 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/types.h>
+#include <sys/cdefs.h>
+#include <kern/panic.h>
+#include <mu/mmu.h>
+#include <vm/vm.h>
+#include <md/vas.h>
+
+/*
+ * See Intel SDM Vol 3A, Section 4.5, Table 4-19
+ */
+#define PTE_ADDR_MASK   0x000FFFFFFFFFF000
+#define PTE_P           BIT(0)        /* Present */
+#define PTE_RW          BIT(1)        /* Writable */
+#define PTE_US          BIT(2)        /* User r/w allowed */
+#define PTE_PWT         BIT(3)        /* Page-level write-through */
+#define PTE_PCD         BIT(4)        /* Page-level cache disable */
+#define PTE_ACC         BIT(5)        /* Accessed */
+#define PTE_DIRTY       BIT(6)        /* Dirty (written-to page) */
+#define PTE_PS          BIT(7)        /* Page size */
+#define PTE_GLOBAL      BIT(8)        /* Global / sticky map */
+#define PTE_NX          BIT(63)       /* Execute-disable */
+
+int
+mu_pmap_readvas(struct mmu_vas *vas)
+{
+    __asmv(
+        "mov %%cr3, %0"
+        : "=r" (vas->cr3)
+        :
+        : "memory"
+    );
+
+    vas->cr3 &= PTE_ADDR_MASK;
+    return 0;
+}
+
+int
+mu_pmap_writevas(struct mmu_vas *vas)
+{
+    __asmv(
+        "mov %0, %%cr3"
+        :
+        : "r" (vas->cr3)
+        : "memory"
+    );
+
+    return 0;
+}
+
+void
+mu_pmap_init(void)
+{
+    struct mmu_vas cur_vas;
+    uintptr_t *pml4;
+
+    /* Tear down the old lower half mappings */
+    mu_pmap_readvas(&cur_vas);
+    pml4 = PHYS_TO_VIRT(cur_vas.cr3);
+    for (uint16_t i = 0; i < 256; ++i) {
+        pml4[i] = 0;
+    }
+
+    /*
+     * The entries in the TLB may still refer to the old lower
+     * half mappings which are now stale... To avoid this biting
+     * us in the ass we should flush the *entire* TLB
+     */
+    mu_pmap_writevas(&cur_vas);
+}