remap_pfn_range如何将内核内存重新映射到用户空间? [英] How remap_pfn_range remaps kernel memory to user space?

问题描述

remap_pfn_range函数(在驱动程序的mmap调用中使用)可用于将内核内存映射到用户空间.怎么做?谁能解释确切的步骤?内核模式是特权模式(PM)，而用户空间是非特权(NPM).在PM中，CPU可以访问所有内存，而在NPM中，某些内存是受限制的-CPU无法访问.调用remap_pfn_range时，用户空间现在可以访问仅限于PM的那部分内存了吗?

remap_pfn_range function (used in mmap call in driver) can be used to map kernel memory to user space. How is it done? Can anyone explain precise steps? Kernel Mode is a privileged mode (PM) while user space is non privileged (NPM). In PM CPU can access all memory while in NPM some memory is restricted - cannot be accessed by CPU. When remap_pfn_range is called, how is that range of memory which was restricted only to PM is now accessible to user space?

在remap_pfn_range代码处，有pgprot_t struct.这是与保护映射有关的结构.什么是保护映射?是上述问题的答案吗?

Looking at remap_pfn_range code there is pgprot_t struct. This is protection mapping related struct. What is protection mapping? Is it the answer to above question?

推荐答案

真的很简单，内核内存(通常)仅具有一个页面表项，其中特定于体系结构的位显示:此页面表项仅在CPU处于内核模式".

It's simple really, kernel memory (usually) simply has a page table entry with the architecture specific bit that says: "this page table entry is only valid while the CPU is in kernel mode".

remap_pfn_range的作用是创建另一个页表条目，并为未设置该位的同一物理内存页使用不同的虚拟地址.

What remap_pfn_range does is create another page table entry, with a different virtual address to the same physical memory page that doesn't have that bit set.

通常，这是个坏主意:-)

Usually, it's a bad idea btw :-)

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