WIP: RISC-V paging

Signed-off-by: Daniel Maslowski <[email protected]>
r9os · Nov 24, 2023 · 4e327e9 · 4e327e9
1 parent 40f9b81
commit 4e327e9
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Showing 2 changed files with 37 additions and 14 deletions.
diff --git a/riscv64/src/l.S b/riscv64/src/l.S
@@ -23,19 +23,23 @@ start:
   // Volume II: RISC-V Privileged Architectures V20211203 p75
   // SXLEN 64, MODE 8: Sv39 aka Page-based 39-bit virtual addressing
 	lui     t0, %hi(boot_page_table)
+  // page size is 4k (2^12) - drop lowest 12 bits
+  srli    t4, t0, 12
 
+  // subtract offset to get the physical address of the root page table
   li      t1, 0xffffffffc0000000 - 0x80000000
-  // physical address of root page table
-  sub     t3, t0, t1
-  srli    t0, t3, 12 // page size 4k (2^12)
-  li      t1, 8 << 60 // mode Sv39
-  or      t0, t0, t1
+  sub     t2, t0, t1
 
-  // last page: 0xffffffff_c0000000 -> 0x80000000 (1G)
+  // page size is 4k (2^12) - drop lowest 12 bits
+  srli    t3, t2, 12
+  // final SATP
+  li      t1, 8 << 60 // mode Sv39
+  or      t0, t3, t1
 
-  slli    t2, t3, 28
-  ori     t2, t2, 0xcf // VRWXAD
-  sw      t2, 8*255(t3) // #255
+  // t3 holds the root page table physical address divided by 4k; shift for flags
+  slli    t1, t4, 10
+  ori     t1, t4, 0xc1 // DAGU XWRV
+  sd      t1, 8*255(t2) // #255
 
   sfence.vma
   csrw    satp, t0

diff --git a/riscv64/src/main.rs b/riscv64/src/main.rs
@@ -271,8 +271,9 @@ impl PageTable {
 
     pub fn get_entry(&self, at: u16) -> PageTableEntry {
         let addr = self.addr + (at as u64 * Self::ENTRY_SIZE);
-        let val = unsafe { read_volatile(addr as *const u64) };
-        val.into()
+        let high = unsafe { read_volatile((addr + 4) as *const u64) };
+        let low = unsafe { read_volatile(addr as *const u64) };
+        ((high << 32) | low).into()
     }
 
     pub fn create_entry(&self) {}
@@ -330,15 +331,33 @@ pub extern "C" fn main9(hartid: usize, dtb_ptr: u64) -> ! {
     println!("  0 {:?}", bpt.get_entry(0));
     println!("  1 {:?}", bpt.get_entry(1));
     println!("  2 {:?}", bpt.get_entry(2));
-    let x1 = read32((bpt_addr + 255 * 8 + 4).try_into().unwrap());
-    let x2 = read32((bpt_addr + 255 * 8).try_into().unwrap());
-    println!("{x1:12x}{x2:12x}");
+    println!();
+    println!();
+
+    let hi = read32((bpt_addr + 255 * 8 + 4).try_into().unwrap());
+    let lo = read32((bpt_addr + 255 * 8).try_into().unwrap());
+    println!("   {hi:08x} {lo:08x}");
     println!("255 {:?}", bpt.get_entry(255));
+
+    println!();
+    println!();
     println!("508 {:?}", bpt.get_entry(508));
     println!("509 {:?}", bpt.get_entry(509));
     println!("510 {:?}", bpt.get_entry(510));
     println!("511 {:?}", bpt.get_entry(511));
+    println!();
+    println!();
 
+    // fixed 25 bits, used 39 bits
+    const VFIXED: usize = 0xff_ff_ff_80__00_00_00_00;
+    let ppn2 = 255 << (9 + 9 + 12);
+    let ppn1 = 255 << (9 + 12);
+    let ppn0 = 255 << 12;
+    let poff = 0x0;
+    let vaddr = VFIXED | ppn2 | ppn1 | ppn0 | poff;
+    println!("{vaddr:016x}");
+    let x1 = read32(vaddr);
+    println!("{x1:08x}");
     #[cfg(not(test))]
     sbi::shutdown();
     #[cfg(test)]