Messages in this thread Patch in this message | | | Date | Mon, 23 Feb 2004 18:27:37 +0800 | From | Coywolf Qi Hunt <> | Subject | Does Flushing the Queue after PG REALLY a Necessity? |
| |
H. Peter Anvin wrote:
> Anyone happen to know of any legitimate reason not to reload %cs in > head.S? I think the following would be a lot cleaner, as well as a > lot safer (the jump and indirect branch aren't guaranteed to have the > proper effects, although technically neither should be required due to > the %cr0 write):
Anyone happen to know of any legitimate reason to flush the prefetch queue after enabling paging?
I've read the intel manual volume 3 thoroughly. It only says that after entering protected mode, flushing is required, but never says specifically about whether to do flushing after enabling paging.
Furthermore the intel example code enables protected mode and paging at the same time. So does FreeBSD. There's really no more references to check.
From the cpu's internal view, flushing for PE is to flush the prefetch queue as well as re-load the %cs, since the protected mode is just about to begin. But no reason to flushing for PG, since linux maps the addresses *identically*.
If no any reason, please remove the after paging flushing queue code, two near jump.
Coywolf
(patch enclosed) -- Coywolf Qi Hunt Admin of http://GreatCN.org and http://LoveCN.org
--- head.S 2004-02-18 11:57:16.000000000 +0800 +++ head-cy.S 2004-02-23 17:19:02.000000000 +0800 @@ -115,11 +115,7 @@ movl %cr0,%eax orl $0x80000000,%eax movl %eax,%cr0 /* ..and set paging (PG) bit */ - jmp 1f /* flush the prefetch-queue */ -1: - movl $1f,%eax - jmp *%eax /* make sure eip is relocated */ -1: + /* Set up the stack pointer */ lss stack_start,%esp
| |