From ed5b28d498b421e3df7a6199d9d42a561ba5114b Mon Sep 17 00:00:00 2001 From: Asya Date: Tue, 21 Feb 2023 17:51:13 +0300 Subject: [PATCH] wip --- kernel/lds/riscv64-virt.ld | 5 +- kernel/src/arch/riscv64/memory.rs | 268 ++++++++++++++++++++++++++++++ kernel/src/arch/riscv64/mod.rs | 33 +++- kernel/src/memory.rs | 28 ++++ 4 files changed, 330 insertions(+), 4 deletions(-) create mode 100644 kernel/src/arch/riscv64/memory.rs diff --git a/kernel/lds/riscv64-virt.ld b/kernel/lds/riscv64-virt.ld index afeefa87..bec4f7bd 100644 --- a/kernel/lds/riscv64-virt.ld +++ b/kernel/lds/riscv64-virt.ld @@ -56,9 +56,8 @@ SECTIONS { } /* FIXME: Currently this has to be aligned to PAGE_SIZE << MAX_ORDER */ - . = ALIGN(4M); - PROVIDE(_usable_memory_start = .); - PROVIDE(_usable_memory_size = 0x88000000 - .); + PROVIDE(_usable_memory_start = ALIGN(4M)); + PROVIDE(_usable_memory_size = 0x88000000 - _usable_memory_start); /DISCARD/ : { *(.comment) diff --git a/kernel/src/arch/riscv64/memory.rs b/kernel/src/arch/riscv64/memory.rs new file mode 100644 index 00000000..60d9970e --- /dev/null +++ b/kernel/src/arch/riscv64/memory.rs @@ -0,0 +1,268 @@ +use core::num; + +use alloc::boxed::Box; +use spin::{Mutex, Once}; +use crate::memory::{MemoryManager, PhysicalAddress, VirtualAddress}; + +use super::PAGE_SIZE; + +pub enum PageSize { + Size4KiB, + Size2MiB, + Size1GiB, + // FIXME: SV48 support + // Size512GiB, + // FIXME: SV57 support + // Size256TiB, +} + +impl PageSize { + fn level(&self) -> usize { + match self { + PageSize::Size4KiB => 0, + PageSize::Size2MiB => 1, + PageSize::Size1GiB => 2, + // FIXME: SV48 and SV57 support + } + } +} + +pub struct PageTable { + entries: [PageEntry; 512] +} + +impl PageTable { + /// Walk the page table to convert a virtual address to a physical address. + /// If a page fault would occur, this returns None. Otherwise, it returns the physical address. + pub fn virt_to_phys(&self, vaddr: VirtualAddress) -> Option { + let vpn = vaddr.vpns(); + + let mut v = &self.entries[vpn[2]]; + for i in (0..=2).rev() { + if v.is_invalid() { + // This is an invalid entry, page fault. + break; + } else if v.is_leaf() { + // In RISC-V, a leaf can be at any level. + + // The offset mask masks off the PPN. Each PPN is 9 bits and they start at bit #12. + // So, our formula 12 + i * 9 + let off_mask = (1 << (12 + i * 9)) - 1; + let vaddr_pgoff = vaddr.as_addr() & off_mask; + let addr = ((v.entry() << 2) as usize) & !off_mask; + return Some((addr | vaddr_pgoff).into()); + } + // Set v to the next entry which is pointed to by this entry. + // However, the address was shifted right by 2 places when stored in the page table + // entry, so we shift it left to get it back into place. + let entry = v.addr().as_ptr::(); + // We do i - 1 here, however we should get None or Some() above + // before we do 0 - 1 = -1. + v = unsafe { entry.add(vpn[i - 1]).as_ref().unwrap() }; + } + + // If we get here, we've exhausted all valid tables and haven't + // found a leaf. + None + } + + /// Maps a virtual address to a physical address + /// flags should contain only the following: + /// Read, Write, Execute, User, and/or Global + /// flags MUST include one or more of the following: + /// Read, Write, Execute + /// The valid bit automatically gets added + pub fn map(&mut self, vaddr: VirtualAddress, paddr: PhysicalAddress, flags: PageEntryFlags, page_size: PageSize) { + assert!(flags as usize & 0xe != 0); + + let vpn = vaddr.vpns(); + let ppn = paddr.ppns(); + let level = page_size.level(); + + let mut v = &mut self.entries[vpn[2]]; + + // Now, we're going to traverse the page table and set the bits properly. We expect the root + // to be valid, however we're required to create anything beyond the root + for i in (level..2).rev() { + if v.is_invalid() { + let mut mm = MEMORY_MANAGER.get().unwrap().lock(); + let page = mm.zallocate_pages(1).unwrap().as_addr(); + v.set_entry((page as usize >> 2) | PageEntryFlags::Valid as usize); + } + + let entry = v.addr().as_mut_ptr::(); + v = unsafe { entry.add(vpn[i]).as_mut().unwrap() }; + } + + // When we get here, we should be at VPN[0] and v should be pointing to our entry. + // The entry structure is Figure 4.18 in the RISC-V Privileged Specification + let entry = (ppn[2] << 28) as usize // PPN[2] = [53:28] + | (ppn[1] << 19) as usize // PPN[1] = [27:19] + | (ppn[0] << 10) as usize // PPN[0] = [18:10] + | flags as usize // Specified bits, such as User, Read, Write, etc. + | PageEntryFlags::Valid as usize; + v.set_entry(entry); + } + + /// Identity maps a page of memory + pub fn identity_map(&mut self, addr: PhysicalAddress, flags: PageEntryFlags, page_size: PageSize) { + // log::debug!("identity mapped {addr}"); + self.map(addr.as_addr().into(), addr, flags, page_size); + } + + /// Identity maps a range of contiguous memory + /// This assumes that start <= end + pub fn identity_map_range(&mut self, start: PhysicalAddress, end: PhysicalAddress, flags: PageEntryFlags) { + log::debug!("start: {start}, end: {end}"); + let mut mem_addr = start.as_addr() & !(PAGE_SIZE - 1); + let num_pages = (align_val(end.as_addr(), 12) - mem_addr - 1) / PAGE_SIZE + 1; + + for _ in 0..num_pages { + // FIXME: we can merge these page entries if possible into Size2MiB or larger entries + self.identity_map(mem_addr.into(), flags, PageSize::Size4KiB); + mem_addr += 1 << 12; + } + } + + /// Unmaps a page of memory at vaddr + pub fn unmap(&mut self, vaddr: VirtualAddress) { + let vpn = vaddr.vpns(); + + // Now, we're going to traverse the page table and clear the bits + let mut v = &mut self.entries[vpn[2]]; + for i in (0..2).rev() { + if v.is_invalid() { + // This is an invalid entry, page is already unmapped + return; + } else if v.is_leaf() { + // This is a leaf, which can be at any level + // In order to make this page unmapped, we need to clear the entry + v.set_entry(0); + return; + } + + let entry = v.addr().as_mut_ptr::(); + v = unsafe { entry.add(vpn[i]).as_mut().unwrap() }; + } + + // If we're here this is an unmapped page + return; + } + + /// Unmaps a range of contiguous memory + /// This assumes that start <= end + pub fn unmap_range(&mut self, start: VirtualAddress, end: VirtualAddress) { + let mut mem_addr = start.as_addr() & !(PAGE_SIZE - 1); + let num_pages = (align_val(end.as_addr(), 12) - mem_addr) / PAGE_SIZE; + + for _ in 0..num_pages { + self.unmap(mem_addr.into()); + mem_addr += 1 << 12; + } + } + + /// Frees all memory associated with a table. + /// NOTE: This does NOT free the table directly. This must be freed manually. + fn destroy(&mut self) { + for entry in &mut self.entries { + entry.destroy() + } + } +} + +#[repr(usize)] +#[derive(Clone, Copy, Debug)] +pub enum PageEntryFlags { + None = 0, + Valid = 1, + Read = 1 << 1, + Write = 1 << 2, + Execute = 1 << 3, + User = 1 << 4, + Global = 1 << 5, + Access = 1 << 6, + Dirty = 1 << 7, + + // for convenience + ReadWrite = Self::Read as usize | Self::Write as usize, + ReadExecute = Self::Read as usize | Self::Execute as usize, + ReadWriteExecute = Self::Read as usize | Self::Write as usize | Self::Execute as usize, + UserReadWrite = Self::User as usize | Self::ReadWrite as usize, + UserReadExecute = Self::User as usize | Self::ReadExecute as usize, + UserReadWriteExecute = Self::User as usize | Self::ReadWriteExecute as usize, +} + +struct PageEntry(usize); + +impl PageEntry { + fn is_valid(&self) -> bool { + self.0 & PageEntryFlags::Valid as usize != 0 + } + + fn is_invalid(&self) -> bool { + !self.is_valid() + } + + fn is_leaf(&self) -> bool { + self.0 & PageEntryFlags::ReadWriteExecute as usize != 0 + } + + fn is_branch(&self) -> bool { + !self.is_leaf() + } + + fn entry(&self) -> usize { + self.0 + } + + fn set_entry(&mut self, entry: usize) { + self.0 = entry; + } + + fn clear_flag(&mut self, flag: PageEntryFlags) { + self.0 &= !(flag as usize); + } + + fn set_flag(&mut self, flag: PageEntryFlags) { + self.0 |= flag as usize; + } + + fn addr(&self) -> PhysicalAddress { + ((self.entry() as usize & !0x3ff) << 2).into() + } + + fn destroy(&mut self) { + if self.is_valid() && self.is_branch() { + // This is a valid entry so drill down and free + let memaddr = self.addr(); + let table = memaddr.as_mut_ptr::(); + unsafe { + (*table).destroy(); + let mut mm = MEMORY_MANAGER.get().unwrap().lock(); + mm.deallocate_pages(memaddr.into(), 0); + } + } + } +} + +// FIXME: PageTable should be integrated into MemoryManager *somehow* +pub static MEMORY_MANAGER: Once> = Once::new(); +pub static PAGE_TABLE: Once> = Once::new(); + +pub fn init(start_addr: PhysicalAddress, page_count: usize) { + let mut memory_manager = MemoryManager::new(); + + unsafe { + memory_manager.add_range(start_addr, page_count); + PAGE_TABLE.call_once(|| Mutex::new(memory_manager.zallocate_pages(0).unwrap())); + } + + MEMORY_MANAGER.call_once(|| Mutex::new(memory_manager)); +} + +/// Align (set to a multiple of some power of two) +/// This function always rounds up. +fn align_val(val: usize, order: usize) -> usize { + let o = (1 << order) - 1; + (val + o) & !o +} diff --git a/kernel/src/arch/riscv64/mod.rs b/kernel/src/arch/riscv64/mod.rs index cd7aeb45..767da039 100644 --- a/kernel/src/arch/riscv64/mod.rs +++ b/kernel/src/arch/riscv64/mod.rs @@ -1,11 +1,12 @@ mod memory; use core::{arch::{asm, global_asm}, fmt::Write}; +use alloc::boxed::Box; use sbi::system_reset::{ResetType, ResetReason, system_reset}; use spin::{Mutex, Once}; use uart_16550::MmioSerialPort; -use crate::{allocator, memory::PhysicalAddress}; +use crate::{allocator, memory::PhysicalAddress, arch::riscv64::memory::{PAGE_TABLE, PageEntryFlags, PageSize, PageTable}}; global_asm!(include_str!("entry.s")); global_asm!(include_str!("memory_regions.s")); @@ -46,6 +47,36 @@ unsafe extern fn _kernel_start() -> ! { allocator::init(INITIAL_KERNEL_HEAP_START.as_mut_ptr::(), INITIAL_KERNEL_HEAP_SIZE); memory::init(USABLE_MEMORY_START.into(), USABLE_MEMORY_SIZE / PAGE_SIZE); + let mut page_table_addr = PAGE_TABLE.get().unwrap().lock(); + let mut page_table = page_table_addr.as_mut_ptr::().as_mut().unwrap(); + + // Map text (executable) section + page_table.identity_map_range(TEXT_START, TEXT_END, PageEntryFlags::ReadExecute); + // Map rodata section + page_table.identity_map_range(RODATA_END, RODATA_END, PageEntryFlags::Read); + // Map data section + page_table.identity_map_range(DATA_START, DATA_END, PageEntryFlags::ReadWrite); + // Map sdata section + page_table.identity_map_range(SDATA_START, SDATA_END, PageEntryFlags::ReadWrite); + // Map bss section (includes stack and initial kernel heap) + page_table.identity_map_range(BSS_START, BSS_END, PageEntryFlags::ReadWrite); + // Map usable memory range (as rw so not executable) + page_table.identity_map_range(USABLE_MEMORY_START, USABLE_MEMORY_START + USABLE_MEMORY_SIZE.into(), PageEntryFlags::ReadWrite); + // Map Uart so we can continue using serial + page_table.identity_map(0x1000_0000_usize.into(), PageEntryFlags::ReadWrite, PageSize::Size4KiB); + + let table_ppn = page_table_addr.as_addr() as usize >> 12; + let satp_value = 8 << 60 | table_ppn; + log::info!("Enabling the MMU..."); + + asm!( + "csrw satp, {}", + "sfence.vma", + in(reg) satp_value, + ); + + log::info!("We're in PAGING LAND!"); + #[allow(unreachable_code)] match system_reset(ResetType::Shutdown, ResetReason::NoReason).unwrap() {} } diff --git a/kernel/src/memory.rs b/kernel/src/memory.rs index 3665497c..15b5db1c 100644 --- a/kernel/src/memory.rs +++ b/kernel/src/memory.rs @@ -49,6 +49,20 @@ pub const MAX_ORDER: usize = 10; pub struct VirtualAddress(usize); impl VirtualAddress { + #[cfg(target_arch = "riscv64")] + /// Returns an array of Virtual Page Numbers + // FIXME: SV48 and SV57 support + pub fn vpns(&self) -> [usize; 3] { + [ + // [20:12] + (self.0 >> 12) & 0x1ff, + // [29:21] + (self.0 >> 21) & 0x1ff, + // [38:30] + (self.0 >> 30) & 0x1ff, + ] + } + pub fn as_addr(&self) -> usize { self.0 } @@ -105,6 +119,20 @@ impl VirtualAddress { pub struct PhysicalAddress(usize); impl PhysicalAddress { + #[cfg(target_arch = "riscv64")] + /// Returns an array of Physical Page Numbers + // FIXME: SV48 and SV57 support + pub fn ppns(&self) -> [usize; 3] { + [ + // [20:12] + (self.0 >> 12) & 0x1ff, + // [29:21] + (self.0 >> 21) & 0x1ff, + // [55:30] + (self.0 >> 30) & 0x3ffffff, + ] + } + pub fn as_addr(&self) -> usize { self.0 }