From efdd64736f22f922f99a2e8c0201088a82ccdc28 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Mon, 27 Feb 2023 12:41:28 +0100
Subject: [PATCH] x86_64: Allow mapping huge pages, but don't do it yet

---
 kernel/src/arch/MMU.h               | 10 +++++++++-
 kernel/src/arch/x86_64/MMU.cpp      | 31 +++++++++++++++++++----------
 kernel/src/arch/x86_64/MMU.h        |  1 +
 kernel/src/memory/MemoryManager.cpp |  8 ++++----
 4 files changed, 35 insertions(+), 15 deletions(-)

diff --git a/kernel/src/arch/MMU.h b/kernel/src/arch/MMU.h
index 031c038e..addd5863 100644
--- a/kernel/src/arch/MMU.h
+++ b/kernel/src/arch/MMU.h
@@ -7,6 +7,8 @@
 #error "Unknown architecture."
 #endif
 
+constexpr u64 PAGES_PER_HUGE_PAGE = ARCH_HUGE_PAGE_SIZE / ARCH_PAGE_SIZE;
+
 namespace MMU
 {
     enum Flags
@@ -19,7 +21,13 @@ namespace MMU
         CacheDisable = 16,
     };
 
-    Result<void> map(u64 virt, u64 phys, int flags);
+    enum class UseHugePages
+    {
+        No = 0,
+        Yes = 1
+    };
+
+    Result<void> map(u64 virt, u64 phys, int flags, UseHugePages use_huge_pages);
     Result<u64> unmap(u64 virt);
     Result<u64> get_physical(u64 virt);
     Result<int> get_flags(u64 virt);
diff --git a/kernel/src/arch/x86_64/MMU.cpp b/kernel/src/arch/x86_64/MMU.cpp
index 0e04332b..de239a22 100644
--- a/kernel/src/arch/x86_64/MMU.cpp
+++ b/kernel/src/arch/x86_64/MMU.cpp
@@ -167,7 +167,18 @@ namespace MMU
         return &l1;
     }
 
-    Result<void> map(u64 virt, u64 phys, int flags)
+    void set_page_table_entry_properties(PageTableEntry& entry, u64 phys, int flags)
+    {
+        entry.present = true;
+        entry.read_write = has_flag(flags, Flags::ReadWrite);
+        entry.user = has_flag(flags, Flags::User);
+        entry.write_through = has_flag(flags, Flags::WriteThrough);
+        entry.cache_disabled = has_flag(flags, Flags::CacheDisable);
+        entry.no_execute = has_flag(flags, Flags::NoExecute);
+        entry.set_address(phys);
+    }
+
+    Result<void> map(u64 virt, u64 phys, int flags, UseHugePages use_huge_pages)
     {
         auto& l4 = l4_entry(virt);
         if (!l4.present)
@@ -191,7 +202,7 @@ namespace MMU
         if (flags & Flags::ReadWrite) l3.read_write = true;
         if (flags & Flags::User) l3.user = true;
 
-        if (l3.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM
+        if (l3.larger_pages) return err(EEXIST);
 
         auto& l2 = l2_entry(l3, virt);
         if (!l2.present)
@@ -204,17 +215,17 @@ namespace MMU
         if (flags & Flags::ReadWrite) l2.read_write = true;
         if (flags & Flags::User) l2.user = true;
 
-        if (l2.larger_pages) return err(EFIXME); // FIXME: Replacing larger pages is not supported ATM
+        if (l2.larger_pages) return err(EEXIST);
+        else if (use_huge_pages == UseHugePages::Yes)
+        {
+            l2.larger_pages = true;
+            set_page_table_entry_properties(l2, phys, flags);
+            return {};
+        }
 
         auto& l1 = l1_entry(l2, virt);
         if (l1.present) return err(EEXIST); // Please explicitly unmap the page before mapping it again.
-        l1.present = true;
-        l1.read_write = has_flag(flags, Flags::ReadWrite);
-        l1.user = has_flag(flags, Flags::User);
-        l1.write_through = has_flag(flags, Flags::WriteThrough);
-        l1.cache_disabled = has_flag(flags, Flags::CacheDisable);
-        l1.no_execute = has_flag(flags, Flags::NoExecute);
-        l1.set_address(phys);
+        set_page_table_entry_properties(l1, phys, flags);
         return {};
     }
 
diff --git a/kernel/src/arch/x86_64/MMU.h b/kernel/src/arch/x86_64/MMU.h
index 198485f0..d1f8c362 100644
--- a/kernel/src/arch/x86_64/MMU.h
+++ b/kernel/src/arch/x86_64/MMU.h
@@ -2,6 +2,7 @@
 #include <luna/Types.h>
 
 const usize ARCH_PAGE_SIZE = 4096;
+const usize ARCH_HUGE_PAGE_SIZE = 2 * 1024 * 1024; // 2 MiB
 
 const u64 rindex = 0776;          // recursive index
 const u64 sign = 0177777UL << 48; // sign extension
diff --git a/kernel/src/memory/MemoryManager.cpp b/kernel/src/memory/MemoryManager.cpp
index 96818eb7..35e6b80a 100644
--- a/kernel/src/memory/MemoryManager.cpp
+++ b/kernel/src/memory/MemoryManager.cpp
@@ -202,7 +202,7 @@ namespace MemoryManager
 
         while (pages_mapped < count)
         {
-            TRY(MMU::map(virt, phys, flags));
+            TRY(MMU::map(virt, phys, flags, MMU::UseHugePages::No));
             virt += ARCH_PAGE_SIZE;
             phys += ARCH_PAGE_SIZE;
             pages_mapped++;
@@ -225,7 +225,7 @@ namespace MemoryManager
         while (pages_mapped < count)
         {
             const u64 frame = TRY(alloc_frame());
-            TRY(MMU::map(virt, frame, flags));
+            TRY(MMU::map(virt, frame, flags, MMU::UseHugePages::No));
             virt += ARCH_PAGE_SIZE;
             pages_mapped++;
         }
@@ -250,7 +250,7 @@ namespace MemoryManager
         while (pages_mapped < count)
         {
             const u64 frame = TRY(alloc_frame());
-            TRY(MMU::map(virt, frame, flags));
+            TRY(MMU::map(virt, frame, flags, MMU::UseHugePages::No));
             virt += ARCH_PAGE_SIZE;
             pages_mapped++;
         }
@@ -275,7 +275,7 @@ namespace MemoryManager
 
         while (pages_mapped < count)
         {
-            TRY(MMU::map(virt, phys, flags));
+            TRY(MMU::map(virt, phys, flags, MMU::UseHugePages::No));
             virt += ARCH_PAGE_SIZE;
             phys += ARCH_PAGE_SIZE;
             pages_mapped++;