Revision as of 08:22, 6 June 2012 view source Spy (talk \| contribs) 2 edits general tidy-up, better phrasing, precise terminology ← Older edit		Revision as of 13:28, 27 June 2012 view source Spy (talk \| contribs) 2 edits →‎Modification of paging structures: AT&T x86 assembly syntax throughout the article (for the sake of consistency) Newer edit →
Line 7: The TLB is not transparently informed of changes made to paging structures. Therefore the TLB has to be flushed upon such a change. On x86 systems, this can be done by writing to the page directory base register (CR3): <source lang="asm"> ~~mov~~movl ~~eax,~~%cr3,%eax ~~mov~~movl ~~cr3,~~%eax,%cr3 </source> Note: setting the global (G) bit in a page directory/table entry will prevent that entry from being flushed. This is useful for pinning interrupt handlers in place. An alternate (and better) method is to use the <code>~~INVLPG~~invlpg</code> instruction, which should be used instead of the above method when doing small mapping modifications (creation, removing, changing.) <code>~~INVLPG~~invlpg</code> is mostly used in page unmapping and remapping routines in order to invalidate a previous cached translation. If <code>~~INVLPG~~invlpg</code> or some other TLB flush method had not been used, the mapping would remain cached, ~~causing~~producing ~~potentially strange behaviour across the~~undefined ~~system~~consequences. However, please note that the <code>~~INVLPG~~invlpg</code> instruction was introduced in the i486 ISA and is not part of the i386 ISA, thereby requiring a properly written i386-compatible kernel to use conditional inclusion of relevant code at compilation time depending on the target machine;. anAn example routine ~~follows~~declaration and source code follow: <source lang="c"> void vm_page_inval(void ); </source> <source lang="asm"> #include <kconfig.h> ~~.globl vm_inval_page~~ ~~vm_inval_page:~~ .globl vm_page_inval ~~#ifdef TARGET_ARCH_I486~~ vm_page_inval: #if TARGET_MACHINE >= TARGET_MACHINE_I486 movl 4(%esp),%eax invlpg (%eax) #else / ~~TARGET_ARCH_I486~~TARGET_MACHINE >= TARGET_MACHINE_I486 / movl %cr3,%eax movl %eax,%cr3 #endif / ~~TARGET_ARCH_I486~~TARGET_MACHINE >= TARGET_MACHINE_I486 */ ret </source>

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