From af26dce0388a2da663d3251fb116ba0b30003377 Mon Sep 17 00:00:00 2001
From: apio <blobs.trading@gmail.com>
Date: Tue, 4 Jul 2023 00:49:26 +0200
Subject: [PATCH] kernel: Zero physical frames instead of virtual pages

The memset() happens a bit earlier, and we don't have to remap the
mapped virtual memory.
---
 kernel/src/memory/MemoryManager.cpp | 31 +++++++++++++++++++++++------
 kernel/src/memory/MemoryManager.h   |  1 +
 2 files changed, 26 insertions(+), 6 deletions(-)

diff --git a/kernel/src/memory/MemoryManager.cpp b/kernel/src/memory/MemoryManager.cpp
index 4ee6e119..7763d4b6 100644
--- a/kernel/src/memory/MemoryManager.cpp
+++ b/kernel/src/memory/MemoryManager.cpp
@@ -151,6 +151,16 @@ namespace MemoryManager
         return index * ARCH_PAGE_SIZE;
     }
 
+    Result<u64> alloc_zeroed_frame()
+    {
+        const u64 frame = TRY(alloc_frame());
+
+        const u64 address = MMU::translate_physical_address(frame);
+        memset((void*)address, 0, ARCH_PAGE_SIZE);
+
+        return frame;
+    }
+
     Result<void> free_frame(u64 frame)
     {
         const u64 index = frame / ARCH_PAGE_SIZE;
@@ -263,15 +273,24 @@ namespace MemoryManager
 
     Result<u64> alloc_at_zeroed(u64 virt, usize count, int flags)
     {
-        u64 address = TRY(alloc_at(virt, count, MMU::ReadWrite));
+        CHECK_PAGE_ALIGNED(virt);
 
-        memset((void*)address, 0, count * ARCH_PAGE_SIZE);
+        u64 start = virt;
+        usize pages_mapped = 0;
 
-        // This should never fail (we just mapped memory at that address) but we don't want to crash the kernel if it
-        // does.
-        TRY(remap(address, count, flags));
+        auto guard = make_scope_guard([=, &pages_mapped] { unmap_owned(start, pages_mapped); });
 
-        return address;
+        while (pages_mapped < count)
+        {
+            const u64 frame = TRY(alloc_zeroed_frame());
+            TRY(MMU::map(virt, frame, flags, MMU::UseHugePages::No));
+            virt += ARCH_PAGE_SIZE;
+            pages_mapped++;
+        }
+
+        guard.deactivate();
+
+        return start;
     }
 
     Result<u64> alloc_for_kernel(usize count, int flags)
diff --git a/kernel/src/memory/MemoryManager.h b/kernel/src/memory/MemoryManager.h
index 443d5095..e16130bd 100644
--- a/kernel/src/memory/MemoryManager.h
+++ b/kernel/src/memory/MemoryManager.h
@@ -13,6 +13,7 @@ namespace MemoryManager
     Result<void> protect_kernel_sections();
 
     Result<u64> alloc_frame();
+    Result<u64> alloc_zeroed_frame();
     Result<void> free_frame(u64 frame);
     Result<void> free_frames(u64 address, usize count);