Messages in this thread | | | Date | Thu, 15 Nov 2007 14:42:46 -0800 | From | "H. Peter Anvin" <> | Subject | Re: Why preallocate pmd in x86 32-bit PAE? |
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Linus Torvalds wrote: > > IIRC, the present bit is ignored in the magic 4-entry PGD. All entries > have to be present. >
This is true, although you could point a PGD to an all-zero page if you really wanted to. You have to re-load CR3 after modifying the top-level entries.
> What earlier CPU's did was to basically load all four values into the CPU > when you loaded %cr3. There was no "three-level page table walker" at all: > it was still a two-level page table walker, there were just for magic > internal page tables that were indexed off the two high bits.
They still are. Loading CR3 in PAE really loads four registers from memory. x86-64 is different, of course.
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