From 858a52c06a4615bd58a6a906333f2ad707d41c0a Mon Sep 17 00:00:00 2001
From: Jon Santmyer <jon@jonsantmyer.com>
Date: Tue, 19 Aug 2025 15:04:04 -0400
Subject: usermode pager

---
 apps/init/arch/x86_64/paging.c | 109 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 109 insertions(+)
 create mode 100644 apps/init/arch/x86_64/paging.c

(limited to 'apps/init/arch/x86_64/paging.c')

diff --git a/apps/init/arch/x86_64/paging.c b/apps/init/arch/x86_64/paging.c
new file mode 100644
index 0000000..6c1c386
--- /dev/null
+++ b/apps/init/arch/x86_64/paging.c
@@ -0,0 +1,109 @@
+#include "../../memory.h"
+#include "jove/object-dir.h"
+#include "jove/jove.h"
+#include <jove/arch/x86_64/object-pagemap.h>
+#include <stdbool.h>
+
+KernelObjectPageMap init_pagemap;
+unsigned d_cache[3] = { -1, -1, -1 };
+uintptr_t vptr_cache = 0;
+
+KernelObjectUntyped work_page;
+
+#define PMLI_SHL(d) (((4 - d) * 9) + 3)
+#define PMLI_DL(v, d) ((v >> PMLI_SHL(d)) % 512)
+
+uint64_t
+pager_write_path(uintptr_t vptr, uint8_t depth)
+{
+    uint64_t r = 0;
+    if(depth >= 4) return -1;
+
+    uint16_t *path = (uint16_t*)&r;
+    for(uint8_t i = 0; i < depth; i++) path[i] = PMLI_DL(vptr, i);
+    return r;
+}
+
+bool
+pager_depth_exists(uintptr_t vptr, uint8_t depth)
+{
+    uint64_t path = pager_write_path(vptr, depth);
+    if(path == -1) return false;
+
+    return jove_pagemap_exists(&init_pagemap, depth, (uint16_t*)&path);
+}
+/* Places new page in work_page. */
+JoveError
+pager_alloc_page_untyped(void)
+{
+    uint8_t lastmemb = jove_objdir_lastmemb(&untypedDirectory);
+    if(jove_errno) {
+        JoveError err = jove_errno;
+        jove_errno = EJOVE_OK;
+        return err;
+    }
+    
+    KernelObjectUntyped last_untyped;
+    _jove_alloc_untyped_inplace(&last_untyped, &untypedDirectory, lastmemb);
+    
+    if(jove_untyped_size(&last_untyped) == 0x1000) {
+        jove_objdir_move(&untypedDirectory, lastmemb, &__rootdir, work_page.typed.membi);
+        return EJOVE_OK;
+    }
+
+    return jove_untyped_split_inplace(&last_untyped, 0x1000, &work_page);
+}
+
+JoveError
+pager_ensure_at_depth(uint8_t depth, uint16_t *path)
+{
+    int exists = jove_pagemap_exists(&init_pagemap, depth, path);
+    if(exists) {
+        return EJOVE_OK;
+    }
+
+    JoveError pagealloc_err = pager_alloc_page_untyped();
+    if(pagealloc_err) {
+        jove_kprintf("Failed to allocate page with error %i\n", pagealloc_err);
+        return pagealloc_err;
+    }
+    return jove_pagemap_map(&init_pagemap, depth, path, &work_page);
+}
+
+#define PAGER_CACHE_ENSURE_DEPTH(path_seg, d) \
+    if(path_seg[d] != d_cache[d]) { \
+        JoveError d_err = pager_ensure_at_depth(d, path_seg); \
+        if(d_err) return d_err; \
+        d_cache[d] = path_seg[d]; \
+    }
+
+JoveError
+pager_ensure(uintptr_t vptr)
+{
+    uint64_t path = pager_write_path(vptr, 3);
+    if(path == -1) return EJOVE_BADARG;
+
+    vptr &= ~0xFFFULL;
+    uint16_t *path_seg = (uint16_t*)&path;
+    jove_kprintf("%x:%x:%x:%x\n", path_seg[0], path_seg[1], path_seg[2], path_seg[3]);
+
+    PAGER_CACHE_ENSURE_DEPTH(path_seg, 0);
+    PAGER_CACHE_ENSURE_DEPTH(path_seg, 1);
+    PAGER_CACHE_ENSURE_DEPTH(path_seg, 2);
+    if(vptr != vptr_cache) {
+        return pager_ensure_at_depth(3, path_seg);
+    }
+    return EJOVE_OK;
+}
+
+void
+pager_setup(void)
+{
+    _jove_alloc_objdir_inplace(&untypedDirectory, &__rootdir, INIT_OBJECT_UNTYPED_DIR);
+    _jove_alloc_pagemap_inplace(&init_pagemap, &__rootdir, INIT_OBJECT_PAGEMAP);
+
+    size_t lastfree = jove_objdir_lastmemb(&__rootdir) + 1;
+    _jove_alloc_untyped_inplace(&work_page, &__rootdir, lastfree++);
+
+    pager_ensure(0x00000000F0000000);
+}
-- 
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