From c0a96aa7e4de7f4987fb58123b4fd0e0f769f93b Mon Sep 17 00:00:00 2001
From: Jeremy Soller <jackpot51@gmail.com>
Date: Tue, 15 Feb 2022 08:53:53 -0700
Subject: [PATCH] Reduce memory used by x86_64 page tables
---
src/arch/x86_64/paging.rs | 45 +++++++++++++++++++--------------------
src/main.rs | 2 +-
2 files changed, 23 insertions(+), 24 deletions(-)
diff --git a/src/arch/x86_64/paging.rs b/src/arch/x86_64/paging.rs
index 5715cd0..847485a 100644
--- a/src/arch/x86_64/paging.rs
+++ b/src/arch/x86_64/paging.rs
@@ -23,13 +23,10 @@ pub unsafe fn paging_create<
D: Disk,
M: Iterator<Item=OsMemoryEntry>,
V: Iterator<Item=OsVideoMode>
->(os: &mut dyn Os<D, M, V>, kernel_phys: usize) -> Option<usize> {
+>(os: &mut dyn Os<D, M, V>, kernel_phys: usize, kernel_size: usize) -> Option<usize> {
// Create PML4
let pml4 = paging_allocate(os)?;
- // Recursive mapping for compatibility
- pml4[511] = pml4.as_ptr() as u64 | 1 << 1 | 1;
-
{
// Create PDP for identity mapping
let pdp = paging_allocate(os)?;
@@ -38,20 +35,15 @@ pub unsafe fn paging_create<
pml4[0] = pdp.as_ptr() as u64 | 1 << 1 | 1;
pml4[256] = pdp.as_ptr() as u64 | 1 << 1 | 1;
- // Identity map 8 GiB pages
+ // Identity map 8 GiB using 2 MiB pages
for pdp_i in 0..8 {
let pd = paging_allocate(os)?;
pdp[pdp_i] = pd.as_ptr() as u64 | 1 << 1 | 1;
for pd_i in 0..pd.len() {
- let pt = paging_allocate(os)?;
- pd[pd_i] = pt.as_ptr() as u64 | 1 << 1 | 1;
- for pt_i in 0..pt.len() {
- let addr =
- pdp_i as u64 * 0x4000_0000 +
- pd_i as u64 * 0x20_0000 +
- pt_i as u64 * 0x1000;
- pt[pt_i] = addr | 1 << 1 | 1;
- }
+ let addr =
+ pdp_i as u64 * 0x4000_0000 +
+ pd_i as u64 * 0x20_0000;
+ pd[pd_i] = addr | 1 << 7 | 1 << 1 | 1;
}
}
}
@@ -63,23 +55,30 @@ pub unsafe fn paging_create<
// Link second to last PML4 entry to PDP
pml4[510] = pdp.as_ptr() as u64 | 1 << 1 | 1;
- // Map 1 GiB at kernel offset
- for pdp_i in 0..1 {
+ // Map kernel_size at kernel offset
+ let mut kernel_mapped = 0;
+ let mut pdp_i = 0;
+ while kernel_mapped < kernel_size && pdp_i < pdp.len() {
let pd = paging_allocate(os)?;
pdp[pdp_i] = pd.as_ptr() as u64 | 1 << 1 | 1;
- for pd_i in 0..pd.len() {
+ pdp_i += 1;
+
+ let mut pd_i = 0;
+ while kernel_mapped < kernel_size && pd_i < pd.len(){
let pt = paging_allocate(os)?;
pd[pd_i] = pt.as_ptr() as u64 | 1 << 1 | 1;
- for pt_i in 0..pt.len() {
- let addr =
- pdp_i as u64 * 0x4000_0000 +
- pd_i as u64 * 0x20_0000 +
- pt_i as u64 * 0x1000 +
- kernel_phys as u64;
+ pd_i += 1;
+
+ let mut pt_i = 0;
+ while kernel_mapped < kernel_size && pt_i < pt.len() {
+ let addr = (kernel_phys + kernel_mapped) as u64;
pt[pt_i] = addr | 1 << 1 | 1;
+ pt_i += 1;
+ kernel_mapped += 4096;
}
}
}
+ assert!(kernel_mapped >= kernel_size);
}
Some(pml4.as_ptr() as usize)
diff --git a/src/main.rs b/src/main.rs
index f7ef087..557ecbe 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -291,7 +291,7 @@ fn main<
kernel
};
- let page_phys = unsafe { paging_create(os, kernel.as_ptr() as usize) }
+ let page_phys = unsafe { paging_create(os, kernel.as_ptr() as usize, kernel.len()) }
.expect("Failed to set up paging");
//TODO: properly reserve page table allocations so kernel does not re-use them
--
GitLab