Merge pull request #408 from rust-osdev/fix-ramdisk

Fix: Mark `ramdisk` as used in memory map

Author: phil-opp

Diff for: common/src/legacy_memory_region.rs

@@ -112,9 +112,12 @@ where
         regions: &mut [MaybeUninit<MemoryRegion>],
         kernel_slice_start: PhysAddr,
         kernel_slice_len: u64,
+        ramdisk_slice_start: Option<PhysAddr>,
+        ramdisk_slice_len: u64,
     ) -> &mut [MemoryRegion] {
         let mut next_index = 0;
         let kernel_slice_start = kernel_slice_start.as_u64();
+        let ramdisk_slice_start = ramdisk_slice_start.map(|a| a.as_u64());
 
         for descriptor in self.original {
             let mut start = descriptor.start();
@@ -157,8 +160,9 @@ where
                 kind,
             };
 
-            // check if region overlaps with kernel
+            // check if region overlaps with kernel or ramdisk
             let kernel_slice_end = kernel_slice_start + kernel_slice_len;
+            let ramdisk_slice_end = ramdisk_slice_start.map(|s| s + ramdisk_slice_len);
             if region.kind == MemoryRegionKind::Usable
                 && kernel_slice_start < region.end
                 && kernel_slice_end > region.start
@@ -198,6 +202,47 @@ where
                 Self::add_region(before_kernel, regions, &mut next_index);
                 Self::add_region(kernel, regions, &mut next_index);
                 Self::add_region(after_kernel, regions, &mut next_index);
+            } else if region.kind == MemoryRegionKind::Usable
+                && ramdisk_slice_start.map(|s| s < region.end).unwrap_or(false)
+                && ramdisk_slice_end.map(|e| e > region.start).unwrap_or(false)
+            {
+                // region overlaps with ramdisk -> we might need to split it
+                let ramdisk_slice_start = ramdisk_slice_start.unwrap();
+                let ramdisk_slice_end = ramdisk_slice_end.unwrap();
+
+                // ensure that the ramdisk allocation does not span multiple regions
+                assert!(
+                    ramdisk_slice_start >= region.start,
+                    "region overlaps with ramdisk, but ramdisk begins before region \
+                (ramdisk_start: {ramdisk_slice_start:#x}, region_start: {:#x})",
+                    region.start
+                );
+                assert!(
+                    ramdisk_slice_end <= region.end,
+                    "region overlaps with ramdisk, but region ends before ramdisk \
+                (ramdisk_end: {ramdisk_slice_end:#x}, region_end: {:#x})",
+                    region.end,
+                );
+
+                // split the region into three parts
+                let before_ramdisk = MemoryRegion {
+                    end: ramdisk_slice_start,
+                    ..region
+                };
+                let ramdisk = MemoryRegion {
+                    start: ramdisk_slice_start,
+                    end: ramdisk_slice_end,
+                    kind: MemoryRegionKind::Bootloader,
+                };
+                let after_ramdisk = MemoryRegion {
+                    start: ramdisk_slice_end,
+                    ..region
+                };
+
+                // add the three regions (empty regions are ignored in `add_region`)
+                Self::add_region(before_ramdisk, regions, &mut next_index);
+                Self::add_region(ramdisk, regions, &mut next_index);
+                Self::add_region(after_ramdisk, regions, &mut next_index);
             } else {
                 // add the region normally
                 Self::add_region(region, regions, &mut next_index);

Diff for: common/src/lib.rs

@@ -293,14 +293,14 @@ where
         None
     };
     let ramdisk_slice_len = system_info.ramdisk_len;
-    let ramdisk_slice_start = if let Some(ramdisk_address) = system_info.ramdisk_addr {
+    let ramdisk_slice_phys_start = system_info.ramdisk_addr.map(PhysAddr::new);
+    let ramdisk_slice_start = if let Some(physical_address) = ramdisk_slice_phys_start {
         let start_page = mapping_addr_page_aligned(
             config.mappings.ramdisk_memory,
             system_info.ramdisk_len,
             &mut used_entries,
             "ramdisk start",
         );
-        let physical_address = PhysAddr::new(ramdisk_address);
         let ramdisk_physical_start_page: PhysFrame<Size4KiB> =
             PhysFrame::containing_address(physical_address);
         let ramdisk_page_count = (system_info.ramdisk_len - 1) / Size4KiB::SIZE;
@@ -404,6 +404,7 @@ where
         kernel_slice_len,
         kernel_image_offset,
 
+        ramdisk_slice_phys_start,
         ramdisk_slice_start,
         ramdisk_slice_len,
     }
@@ -433,6 +434,7 @@ pub struct Mappings {
     pub kernel_slice_len: u64,
     /// Relocation offset of the kernel image in virtual memory.
     pub kernel_image_offset: VirtAddr,
+    pub ramdisk_slice_phys_start: Option<PhysAddr>,
     pub ramdisk_slice_start: Option<VirtAddr>,
     pub ramdisk_slice_len: u64,
 }
@@ -516,6 +518,8 @@ where
         memory_regions,
         mappings.kernel_slice_start,
         mappings.kernel_slice_len,
+        mappings.ramdisk_slice_phys_start,
+        mappings.ramdisk_slice_len,
     );
 
     log::info!("Create bootinfo");

Diff for: tests/ramdisk.rs

@@ -18,3 +18,11 @@ fn check_ramdisk() {
         Some(Path::new(RAMDISK_PATH)),
     );
 }
+
+#[test]
+fn memory_map() {
+    run_test_kernel_with_ramdisk(
+        env!("CARGO_BIN_FILE_TEST_KERNEL_RAMDISK_memory_map"),
+        Some(Path::new(RAMDISK_PATH)),
+    );
+}

Diff for: tests/test_kernels/ramdisk/src/bin/memory_map.rs

@@ -0,0 +1,88 @@
+#![no_std] // don't link the Rust standard library
+#![no_main] // disable all Rust-level entry points
+
+use bootloader_api::{
+    config::Mapping, entry_point, info::MemoryRegionKind, BootInfo, BootloaderConfig,
+};
+use core::{fmt::Write, ptr::slice_from_raw_parts};
+use test_kernel_ramdisk::{exit_qemu, serial, QemuExitCode, RAMDISK_CONTENTS};
+use x86_64::{
+    structures::paging::{OffsetPageTable, PageTable, PageTableFlags, Translate},
+    VirtAddr,
+};
+
+pub const BOOTLOADER_CONFIG: BootloaderConfig = {
+    let mut config = BootloaderConfig::new_default();
+    config.mappings.physical_memory = Some(Mapping::FixedAddress(0x0000_6000_0000_0000));
+    config
+};
+
+entry_point!(kernel_main, config = &BOOTLOADER_CONFIG);
+
+fn kernel_main(boot_info: &'static mut BootInfo) -> ! {
+    writeln!(serial(), "Boot info: {boot_info:?}").unwrap();
+
+    let phys_mem_offset = VirtAddr::new(boot_info.physical_memory_offset.into_option().unwrap());
+    let level_4_table = unsafe { active_level_4_table(phys_mem_offset) };
+    let page_table = unsafe { OffsetPageTable::new(level_4_table, phys_mem_offset) };
+
+    let ramdisk_start_addr = VirtAddr::new(boot_info.ramdisk_addr.into_option().unwrap());
+    assert_eq!(boot_info.ramdisk_len as usize, RAMDISK_CONTENTS.len());
+    let ramdisk_end_addr = ramdisk_start_addr + boot_info.ramdisk_len;
+
+    let mut next_addr = ramdisk_start_addr;
+    while next_addr < ramdisk_end_addr {
+        let phys_addr = match page_table.translate(next_addr) {
+            x86_64::structures::paging::mapper::TranslateResult::Mapped {
+                frame,
+                offset: _,
+                flags,
+            } => {
+                assert!(flags.contains(PageTableFlags::PRESENT));
+                assert!(flags.contains(PageTableFlags::WRITABLE));
+
+                next_addr += frame.size();
+
+                frame.start_address()
+            }
+            other => panic!("invalid result: {other:?}"),
+        };
+        let region = boot_info
+            .memory_regions
+            .iter()
+            .find(|r| r.start <= phys_addr.as_u64() && r.end > phys_addr.as_u64())
+            .unwrap();
+        assert_eq!(region.kind, MemoryRegionKind::Bootloader);
+    }
+
+    let actual_ramdisk = unsafe {
+        &*slice_from_raw_parts(
+            boot_info.ramdisk_addr.into_option().unwrap() as *const u8,
+            boot_info.ramdisk_len as usize,
+        )
+    };
+    writeln!(serial(), "Actual contents: {actual_ramdisk:?}").unwrap();
+    assert_eq!(RAMDISK_CONTENTS, actual_ramdisk);
+
+    exit_qemu(QemuExitCode::Success);
+}
+
+/// This function is called on panic.
+#[cfg(not(test))]
+#[panic_handler]
+fn panic(info: &core::panic::PanicInfo) -> ! {
+    let _ = writeln!(test_kernel_ramdisk::serial(), "PANIC: {info}");
+    exit_qemu(QemuExitCode::Failed);
+}
+
+pub unsafe fn active_level_4_table(physical_memory_offset: VirtAddr) -> &'static mut PageTable {
+    use x86_64::registers::control::Cr3;
+
+    let (level_4_table_frame, _) = Cr3::read();
+
+    let phys = level_4_table_frame.start_address();
+    let virt = physical_memory_offset + phys.as_u64();
+    let page_table_ptr: *mut PageTable = virt.as_mut_ptr();
+
+    &mut *page_table_ptr // unsafe
+}