DragonOS/kernel/src/mm/fault.rs

use core::{
    alloc::Layout,
    cmp::{max, min},
    intrinsics::unlikely,
    panic,
};

use alloc::sync::Arc;

use crate::{
    arch::{mm::PageMapper, MMArch},
    libs::align::align_down,
    mm::{
        page::{page_manager_lock_irqsave, EntryFlags},
        ucontext::LockedVMA,
        VirtAddr, VmFaultReason, VmFlags,
    },
    process::{ProcessManager, ProcessState},
};

use crate::mm::MemoryManagementArch;

use super::{
    allocator::page_frame::FrameAllocator,
    page::{page_reclaimer_lock_irqsave, Page, PageFlags},
};

bitflags! {
    pub struct FaultFlags: u64{
        const FAULT_FLAG_WRITE = 1 << 0;
        const FAULT_FLAG_MKWRITE = 1 << 1;
        const FAULT_FLAG_ALLOW_RETRY = 1 << 2;
        const FAULT_FLAG_RETRY_NOWAIT = 1 << 3;
        const FAULT_FLAG_KILLABLE = 1 << 4;
        const FAULT_FLAG_TRIED = 1 << 5;
        const FAULT_FLAG_USER = 1 << 6;
        const FAULT_FLAG_REMOTE = 1 << 7;
        const FAULT_FLAG_INSTRUCTION = 1 << 8;
        const FAULT_FLAG_INTERRUPTIBLE =1 << 9;
        const FAULT_FLAG_UNSHARE = 1 << 10;
        const FAULT_FLAG_ORIG_PTE_VALID = 1 << 11;
        const FAULT_FLAG_VMA_LOCK = 1 << 12;
    }
}

/// # 缺页异常信息结构体
/// 包含了页面错误处理的相关信息，例如出错的地址、VMA等
#[derive(Debug)]
pub struct PageFaultMessage<'a> {
    /// 产生缺页的VMA结构体
    vma: Arc<LockedVMA>,
    /// 缺页地址
    address: VirtAddr,
    /// 异常处理标志
    flags: FaultFlags,
    /// 页表映射器
    mapper: &'a mut PageMapper,
    /// 缺页的文件页在文件中的偏移量
    file_pgoff: Option<usize>,
    /// 缺页对应PageCache中的文件页
    page: Option<Arc<Page>>,
    /// 写时拷贝需要的页面
    cow_page: Option<Arc<Page>>,
}

impl<'a> PageFaultMessage<'a> {
    pub fn new(
        vma: Arc<LockedVMA>,
        address: VirtAddr,
        flags: FaultFlags,
        mapper: &'a mut PageMapper,
    ) -> Self {
        let guard = vma.lock_irqsave();
        let file_pgoff = guard.file_page_offset().map(|file_page_offset| {
            ((address - guard.region().start()) >> MMArch::PAGE_SHIFT) + file_page_offset
        });
        Self {
            vma: vma.clone(),
            address,
            flags,
            file_pgoff,
            page: None,
            mapper,
            cow_page: None,
        }
    }

    #[inline(always)]
    #[allow(dead_code)]
    pub fn vma(&self) -> Arc<LockedVMA> {
        self.vma.clone()
    }

    #[inline(always)]
    #[allow(dead_code)]
    pub fn address(&self) -> VirtAddr {
        self.address
    }

    #[inline(always)]
    #[allow(dead_code)]
    pub fn address_aligned_down(&self) -> VirtAddr {
        VirtAddr::new(crate::libs::align::page_align_down(self.address.data()))
    }

    #[inline(always)]
    #[allow(dead_code)]
    pub fn flags(&self) -> FaultFlags {
        self.flags
    }
}

/// 缺页中断处理结构体
pub struct PageFaultHandler;

impl PageFaultHandler {
    /// 处理缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn handle_mm_fault(mut pfm: PageFaultMessage) -> VmFaultReason {
        let flags = pfm.flags();
        let vma = pfm.vma();
        let current_pcb = ProcessManager::current_pcb();
        let mut guard = current_pcb.sched_info().inner_lock_write_irqsave();
        guard.set_state(ProcessState::Runnable);

        if !MMArch::vma_access_permitted(
            vma.clone(),
            flags.contains(FaultFlags::FAULT_FLAG_WRITE),
            flags.contains(FaultFlags::FAULT_FLAG_INSTRUCTION),
            flags.contains(FaultFlags::FAULT_FLAG_REMOTE),
        ) {
            return VmFaultReason::VM_FAULT_SIGSEGV;
        }

        let guard = vma.lock_irqsave();
        let vm_flags = *guard.vm_flags();
        drop(guard);
        if unlikely(vm_flags.contains(VmFlags::VM_HUGETLB)) {
            //TODO: 添加handle_hugetlb_fault处理大页缺页异常
        } else {
            Self::handle_normal_fault(&mut pfm);
        }

        VmFaultReason::VM_FAULT_COMPLETED
    }

    /// 处理普通页缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn handle_normal_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let address = pfm.address_aligned_down();
        let vma = pfm.vma.clone();
        let mapper = &mut pfm.mapper;
        if mapper.get_entry(address, 3).is_none() {
            mapper
                .allocate_table(address, 2)
                .expect("failed to allocate PUD table");
        }
        let page_flags = vma.lock_irqsave().flags();

        for level in 2..=3 {
            let level = MMArch::PAGE_LEVELS - level;
            if mapper.get_entry(address, level).is_none() {
                if vma.is_hugepage() {
                    if vma.is_anonymous() {
                        mapper.map_huge_page(address, page_flags);
                    }
                } else if mapper.allocate_table(address, level - 1).is_none() {
                    return VmFaultReason::VM_FAULT_OOM;
                }
            }
        }

        Self::handle_pte_fault(pfm)
    }

    /// 处理页表项异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn handle_pte_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let address = pfm.address_aligned_down();
        let flags = pfm.flags;
        let vma = pfm.vma.clone();
        let mut ret = VmFaultReason::VM_FAULT_COMPLETED;
        let mapper = &pfm.mapper;

        // pte存在
        if let Some(mut entry) = mapper.get_entry(address, 0) {
            if !entry.present() {
                ret = Self::do_swap_page(pfm);
            }

            if entry.protnone() && vma.is_accessible() {
                ret = Self::do_numa_page(pfm);
            }

            if flags.intersects(FaultFlags::FAULT_FLAG_WRITE | FaultFlags::FAULT_FLAG_UNSHARE) {
                if !entry.write() {
                    ret = Self::do_wp_page(pfm);
                } else {
                    entry.set_flags(EntryFlags::from_data(MMArch::ENTRY_FLAG_DIRTY));
                }
            }
        } else if vma.is_anonymous() {
            ret = Self::do_anonymous_page(pfm);
        } else {
            ret = Self::do_fault(pfm);
        }

        vma.lock_irqsave().set_mapped(true);

        return ret;
    }

    /// 处理匿名映射页缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_anonymous_page(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let address = pfm.address_aligned_down();
        let vma = pfm.vma.clone();
        let guard = vma.lock_irqsave();
        let mapper = &mut pfm.mapper;

        if let Some(flush) = mapper.map(address, guard.flags()) {
            flush.flush();
            crate::debug::klog::mm::mm_debug_log(
                klog_types::AllocatorLogType::LazyAlloc(klog_types::AllocLogItem::new(
                    Layout::from_size_align(MMArch::PAGE_SIZE, MMArch::PAGE_SIZE).unwrap(),
                    Some(address.data()),
                    Some(mapper.translate(address).unwrap().0.data()),
                )),
                klog_types::LogSource::Buddy,
            );
            let paddr = mapper.translate(address).unwrap().0;
            let mut page_manager_guard = page_manager_lock_irqsave();
            let page = page_manager_guard.get_unwrap(&paddr);
            page.write_irqsave().insert_vma(vma.clone());
            VmFaultReason::VM_FAULT_COMPLETED
        } else {
            VmFaultReason::VM_FAULT_OOM
        }
    }

    /// 处理文件映射页的缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        if !pfm.flags().contains(FaultFlags::FAULT_FLAG_WRITE) {
            return Self::do_read_fault(pfm);
        } else if !pfm
            .vma()
            .lock_irqsave()
            .vm_flags()
            .contains(VmFlags::VM_SHARED)
        {
            return Self::do_cow_fault(pfm);
        } else {
            return Self::do_shared_fault(pfm);
        }
    }

    /// 处理私有文件映射的写时复制
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_cow_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let mut ret = Self::filemap_fault(pfm);

        if unlikely(ret.intersects(
            VmFaultReason::VM_FAULT_ERROR
                | VmFaultReason::VM_FAULT_NOPAGE
                | VmFaultReason::VM_FAULT_RETRY
                | VmFaultReason::VM_FAULT_DONE_COW,
        )) {
            return ret;
        }

        let cache_page = pfm.page.clone().unwrap();
        let mapper = &mut pfm.mapper;

        let cow_page_phys = mapper.allocator_mut().allocate_one();
        if cow_page_phys.is_none() {
            return VmFaultReason::VM_FAULT_OOM;
        }
        let cow_page_phys = cow_page_phys.unwrap();

        let cow_page = Arc::new(Page::new(false, cow_page_phys));
        pfm.cow_page = Some(cow_page.clone());

        //复制PageCache内容到新的页内
        let new_frame = MMArch::phys_2_virt(cow_page_phys).unwrap();
        (new_frame.data() as *mut u8).copy_from_nonoverlapping(
            MMArch::phys_2_virt(cache_page.read_irqsave().phys_address())
                .unwrap()
                .data() as *mut u8,
            MMArch::PAGE_SIZE,
        );

        let mut page_manager_guard = page_manager_lock_irqsave();

        // 新页加入页管理器中
        page_manager_guard.insert(cow_page_phys, &cow_page);
        cow_page.write_irqsave().set_page_cache_index(
            cache_page.read_irqsave().page_cache(),
            cache_page.read_irqsave().index(),
        );

        // 将vma插入页的vma表中
        cow_page.write_irqsave().insert_vma(pfm.vma());

        ret = ret.union(Self::finish_fault(pfm));

        ret
    }

    /// 处理文件映射页的缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_read_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let fs = pfm.vma().lock_irqsave().vm_file().unwrap().inode().fs();

        let mut ret = Self::do_fault_around(pfm);
        if !ret.is_empty() {
            return ret;
        }

        ret = fs.fault(pfm);

        ret = ret.union(Self::finish_fault(pfm));

        ret
    }

    /// 处理对共享文件映射区写入引起的缺页
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_shared_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let mut ret = Self::filemap_fault(pfm);

        let cache_page = pfm.page.clone().expect("no cache_page in PageFaultMessage");

        // 将pagecache页设为脏页，以便回收时能够回写
        cache_page.write_irqsave().add_flags(PageFlags::PG_DIRTY);
        ret = ret.union(Self::finish_fault(pfm));

        ret
    }

    /// 处理被置换页面的缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    #[allow(unused_variables)]
    pub unsafe fn do_swap_page(pfm: &mut PageFaultMessage) -> VmFaultReason {
        panic!(
            "do_swap_page has not yet been implemented, 
        fault message: {:?}, 
        pid: {}\n",
            pfm,
            crate::process::ProcessManager::current_pid().data()
        );
        // TODO https://code.dragonos.org.cn/xref/linux-6.6.21/mm/memory.c#do_swap_page
    }

    /// 处理NUMA的缺页异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    #[allow(unused_variables)]
    pub unsafe fn do_numa_page(pfm: &mut PageFaultMessage) -> VmFaultReason {
        panic!(
            "do_numa_page has not yet been implemented, 
        fault message: {:?}, 
        pid: {}\n",
            pfm,
            crate::process::ProcessManager::current_pid().data()
        );
        // TODO https://code.dragonos.org.cn/xref/linux-6.6.21/mm/memory.c#do_numa_page
    }

    /// 处理写保护页面的写保护异常
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_wp_page(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let address = pfm.address_aligned_down();
        let vma = pfm.vma.clone();
        let mapper = &mut pfm.mapper;

        let old_paddr = mapper.translate(address).unwrap().0;
        let mut page_manager = page_manager_lock_irqsave();
        let old_page = page_manager.get_unwrap(&old_paddr);
        let map_count = old_page.read_irqsave().map_count();
        drop(page_manager);

        let mut entry = mapper.get_entry(address, 0).unwrap();
        let new_flags = entry.flags().set_write(true).set_dirty(true);

        if vma.lock().vm_flags().contains(VmFlags::VM_SHARED) {
            // 共享映射，直接修改页表项保护位，标记为脏页
            let table = mapper.get_table(address, 0).unwrap();
            let i = table.index_of(address).unwrap();
            entry.set_flags(new_flags);
            table.set_entry(i, entry);

            old_page.write_irqsave().add_flags(PageFlags::PG_DIRTY);

            VmFaultReason::VM_FAULT_COMPLETED
        } else if vma.is_anonymous() {
            // 私有匿名映射，根据引用计数判断是否拷贝页面
            if map_count == 1 {
                let table = mapper.get_table(address, 0).unwrap();
                let i = table.index_of(address).unwrap();
                entry.set_flags(new_flags);
                table.set_entry(i, entry);
                VmFaultReason::VM_FAULT_COMPLETED
            } else if let Some(flush) = mapper.map(address, new_flags) {
                let mut page_manager_guard = page_manager_lock_irqsave();
                let old_page = page_manager_guard.get_unwrap(&old_paddr);
                old_page.write_irqsave().remove_vma(&vma);
                // drop(page_manager_guard);

                flush.flush();
                let paddr = mapper.translate(address).unwrap().0;
                // let mut page_manager_guard = page_manager_lock_irqsave();
                let page = page_manager_guard.get_unwrap(&paddr);
                page.write_irqsave().insert_vma(vma.clone());

                (MMArch::phys_2_virt(paddr).unwrap().data() as *mut u8).copy_from_nonoverlapping(
                    MMArch::phys_2_virt(old_paddr).unwrap().data() as *mut u8,
                    MMArch::PAGE_SIZE,
                );

                VmFaultReason::VM_FAULT_COMPLETED
            } else {
                VmFaultReason::VM_FAULT_OOM
            }
        } else {
            // 私有文件映射，必须拷贝页面
            if let Some(flush) = mapper.map(address, new_flags) {
                let mut page_manager_guard = page_manager_lock_irqsave();
                let old_page = page_manager_guard.get_unwrap(&old_paddr);
                old_page.write_irqsave().remove_vma(&vma);
                // drop(page_manager_guard);

                flush.flush();
                let paddr = mapper.translate(address).unwrap().0;
                // let mut page_manager_guard = page_manager_lock_irqsave();
                let page = page_manager_guard.get_unwrap(&paddr);
                page.write_irqsave().insert_vma(vma.clone());

                (MMArch::phys_2_virt(paddr).unwrap().data() as *mut u8).copy_from_nonoverlapping(
                    MMArch::phys_2_virt(old_paddr).unwrap().data() as *mut u8,
                    MMArch::PAGE_SIZE,
                );

                VmFaultReason::VM_FAULT_COMPLETED
            } else {
                VmFaultReason::VM_FAULT_OOM
            }
        }
    }

    /// 缺页附近页预读
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn do_fault_around(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let vma = pfm.vma();
        let address = pfm.address();
        let mapper = &mut pfm.mapper;

        if mapper.get_table(address, 0).is_none() {
            mapper
                .allocate_table(address, 0)
                .expect("failed to allocate pte table");
        }
        let vma_guard = vma.lock_irqsave();
        let vma_region = *vma_guard.region();
        drop(vma_guard);

        // 缺页在VMA中的偏移量
        let vm_pgoff = (address - vma_region.start()) >> MMArch::PAGE_SHIFT;

        // 缺页在PTE中的偏移量
        let pte_pgoff = (address.data() >> MMArch::PAGE_SHIFT) & (1 << MMArch::PAGE_ENTRY_SHIFT);

        // 缺页在文件中的偏移量
        let file_pgoff = pfm.file_pgoff.expect("no file_pgoff");

        let vma_pages_count = (vma_region.end() - vma_region.start()) >> MMArch::PAGE_SHIFT;

        let fault_around_page_number = 16;

        // 开始位置不能超出当前pte和vma头部
        let from_pte = max(
            align_down(pte_pgoff, fault_around_page_number),
            pte_pgoff - min(vm_pgoff, pte_pgoff),
        );

        // pte结束位置不能超过：
        // 1.最大预读上限（默认16）
        // 2.最大pte(512)
        // 3.vma结束位置(pte_pgoff + (vma_pages_count - vm_pgoff)计算出vma结束页号对当前pte开头的偏移)
        let to_pte = min(
            from_pte + fault_around_page_number,
            min(
                1 << MMArch::PAGE_SHIFT,
                pte_pgoff + (vma_pages_count - vm_pgoff),
            ),
        );

        // 预先分配pte页表（如果不存在）
        if mapper.get_table(address, 0).is_none() && mapper.allocate_table(address, 0).is_none() {
            return VmFaultReason::VM_FAULT_OOM;
        }

        let fs = pfm.vma().lock_irqsave().vm_file().unwrap().inode().fs();
        // from_pte - pte_pgoff得出预读起始pte相对缺失页的偏移，加上pfm.file_pgoff（缺失页在文件中的偏移）得出起始页在文件中的偏移，结束pte同理
        fs.map_pages(
            pfm,
            file_pgoff + (from_pte - pte_pgoff),
            file_pgoff + (to_pte - pte_pgoff),
        );

        VmFaultReason::empty()
    }

    /// 通用的VMA文件映射页面映射函数，将PageCache中的页面映射到进程空间
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn filemap_map_pages(
        pfm: &mut PageFaultMessage,

        start_pgoff: usize,
        end_pgoff: usize,
    ) -> VmFaultReason {
        let vma = pfm.vma();
        let vma_guard = vma.lock_irqsave();
        let file = vma_guard.vm_file().expect("no vm_file in vma");
        let page_cache = file.inode().page_cache().unwrap();
        let mapper = &mut pfm.mapper;

        // 起始页地址
        let addr = vma_guard.region().start
            + ((start_pgoff
                - vma_guard
                    .file_page_offset()
                    .expect("file_page_offset is none"))
                << MMArch::PAGE_SHIFT);

        for pgoff in start_pgoff..=end_pgoff {
            if let Some(page) = page_cache.get_page(pgoff) {
                let page_guard = page.read_irqsave();
                if page_guard.flags().contains(PageFlags::PG_UPTODATE) {
                    let phys = page_guard.phys_address();

                    let address =
                        VirtAddr::new(addr.data() + ((pgoff - start_pgoff) << MMArch::PAGE_SHIFT));
                    mapper
                        .map_phys(address, phys, vma_guard.flags())
                        .unwrap()
                        .flush();
                }
            }
        }
        VmFaultReason::empty()
    }

    /// 通用的VMA文件映射错误处理函数
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn filemap_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let vma = pfm.vma();
        let vma_guard = vma.lock_irqsave();
        let file = vma_guard.vm_file().expect("no vm_file in vma");
        let page_cache = file.inode().page_cache().unwrap();
        let file_pgoff = pfm.file_pgoff.expect("no file_pgoff");
        let mapper = &mut pfm.mapper;
        let mut ret = VmFaultReason::empty();

        if let Some(page) = page_cache.get_page(file_pgoff) {
            // TODO 异步从磁盘中预读页面进PageCache

            // 直接将PageCache中的页面作为要映射的页面
            pfm.page = Some(page.clone());
        } else {
            // TODO 同步预读
            //涉及磁盘IO，返回标志为VM_FAULT_MAJOR
            ret = VmFaultReason::VM_FAULT_MAJOR;
            // let mut buf: Vec<u8> = vec![0; MMArch::PAGE_SIZE];

            let allocator = mapper.allocator_mut();

            // 分配一个物理页面作为加入PageCache的新页
            let new_cache_page = allocator.allocate_one().unwrap();
            // (MMArch::phys_2_virt(new_cache_page).unwrap().data() as *mut u8)
            //     .copy_from_nonoverlapping(buf.as_mut_ptr(), MMArch::PAGE_SIZE);
            file.pread(
                file_pgoff * MMArch::PAGE_SIZE,
                MMArch::PAGE_SIZE,
                core::slice::from_raw_parts_mut(
                    MMArch::phys_2_virt(new_cache_page).unwrap().data() as *mut u8,
                    MMArch::PAGE_SIZE,
                ),
            )
            .expect("failed to read file to create pagecache page");

            let page = Arc::new(Page::new(true, new_cache_page));
            pfm.page = Some(page.clone());

            page.write_irqsave().add_flags(PageFlags::PG_LRU);
            page_manager_lock_irqsave().insert(new_cache_page, &page);
            page_reclaimer_lock_irqsave().insert_page(new_cache_page, &page);
            page_cache.add_page(file_pgoff, &page);

            page.write_irqsave()
                .set_page_cache_index(Some(page_cache), Some(file_pgoff));
        }
        ret
    }

    /// 将文件页映射到缺页地址
    /// ## 参数
    ///
    /// - `pfm`: 缺页异常信息
    /// - `mapper`: 页表映射器
    ///
    /// ## 返回值
    /// - VmFaultReason: 页面错误处理信息标志
    pub unsafe fn finish_fault(pfm: &mut PageFaultMessage) -> VmFaultReason {
        let vma = pfm.vma();
        let vma_guard = vma.lock_irqsave();
        let flags = pfm.flags();
        let cache_page = pfm.page.clone();
        let cow_page = pfm.cow_page.clone();
        let address = pfm.address();
        let mapper = &mut pfm.mapper;

        let page_to_map = if flags.contains(FaultFlags::FAULT_FLAG_WRITE)
            && !vma_guard.vm_flags().contains(VmFlags::VM_SHARED)
        {
            // 私有文件映射的写时复制
            cow_page.expect("no cow_page in PageFaultMessage")
        } else {
            // 直接映射到PageCache
            cache_page.expect("no cache_page in PageFaultMessage")
        };

        let page_phys = page_to_map.read_irqsave().phys_address();

        mapper.map_phys(address, page_phys, vma_guard.flags());
        page_to_map.write_irqsave().insert_vma(pfm.vma());
        VmFaultReason::VM_FAULT_COMPLETED
    }
}