What is a WP?

[Mark Hobley]

I am looking at some source code written for the Linux kernel. There is
a reference X86_WP_WORKS_OK and some related comments about whether or
not the processor has a working WP. I am just wondering, what the hell that
means. What is a WP? I have never heard of this.

Mark.

 

[Dick Wesseling]

I am looking at some source code written for the Linux kernel. There is
a reference X86_WP_WORKS_OK and some related comments about whether or
not the processor has a working WP. I am just wondering, what the hell that
means. What is a WP? I have never heard of this.

Write Protection.

WP is used to implement Copy On Write. When sharing a page between
several processes, the page is marked read-only. Attempts to write
into such a page trap to an error handler in the OS which then makes
a private - writable - copy of the page.

The original 386 honored WP only in user mode, not at level 0. This
requires a software work around.