linux-kernel - [PATCH 2 of 4] x86: revert "defer cr3 reload when doing pud

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Date:	Fri, 01 Feb 2008 08:39:22 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	LKML <linux-kernel@...r.kernel.org>, Andi Kleen <ak@...e.de>,
	Jan Beulich <jbeulich@...ell.com>,
	Eduardo Pereira Habkost <ehabkost@...hat.com>,
	Ian Campbell <ijc@...lion.org.uk>,
	H Peter Anvin <hpa@...or.com>
Subject: [PATCH 2 of 4] x86: revert "defer cr3 reload when doing pud_clear()"

Revert "defer cr3 reload when doing pud_clear()" since I'm going to
replace it.

Signed-off-by: Jeremy Fitzhardinge <jeremy@...source.com>
---
 arch/x86/mm/pgtable_32.c         |    7 -------
 include/asm-x86/pgtable-3level.h |   21 ++++++---------------
 2 files changed, 6 insertions(+), 22 deletions(-)

diff --git a/arch/x86/mm/pgtable_32.c b/arch/x86/mm/pgtable_32.c
--- a/arch/x86/mm/pgtable_32.c
+++ b/arch/x86/mm/pgtable_32.c
@@ -373,13 +373,6 @@
 
 void __pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd)
 {
-	/* This is called just after the pmd has been detached from
-	   the pgd, which requires a full tlb flush to be recognized
-	   by the CPU.  Rather than incurring multiple tlb flushes
-	   while the address space is being pulled down, make the tlb
-	   gathering machinery do a full flush when we're done. */
-	tlb->fullmm = 1;
-
 	paravirt_release_pd(__pa(pmd) >> PAGE_SHIFT);
 	tlb_remove_page(tlb, virt_to_page(pmd));
 }
diff --git a/include/asm-x86/pgtable-3level.h b/include/asm-x86/pgtable-3level.h
--- a/include/asm-x86/pgtable-3level.h
+++ b/include/asm-x86/pgtable-3level.h
@@ -96,23 +96,14 @@
 	set_pud(pudp, __pud(0));
 
 	/*
-	 * In principle we need to do a cr3 reload here to make sure
-	 * the processor recognizes the changed pgd.  In practice, all
-	 * the places where pud_clear() gets called are followed by
-	 * full tlb flushes anyway, so we can defer the cost here.
+	 * Pentium-II erratum A13: in PAE mode we explicitly have to flush
+	 * the TLB via cr3 if the top-level pgd is changed...
 	 *
-	 * Specifically:
-	 *
-	 * mm/memory.c:free_pmd_range() - immediately after the
-	 * pud_clear() it does a pmd_free_tlb().  We change the
-	 * mmu_gather structure to do a full tlb flush (which has the
-	 * effect of reloading cr3) when the pagetable free is
-	 * complete.
-	 *
-	 * arch/x86/mm/hugetlbpage.c:huge_pmd_unshare() - the call to
-	 * this is followed by a flush_tlb_range, which on x86 does a
-	 * full tlb flush.
+	 * XXX I don't think we need to worry about this here, since
+	 * when clearing the pud, the calling code needs to flush the
+	 * tlb anyway.  But do it now for safety's sake. - jsgf
 	 */
+	write_cr3(read_cr3());
 }
 
 #define pud_page(pud) \


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