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x86: pud_clear: only reload cr3 if necessary

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Rather than unconditionally reloading cr3, only do so if the pud we're
updating is within the active pgd.

This eliminates TLB flushes most of the time.  The
performance-critical uses of pud_clear are during execve and exit, but
in those cases cr3 is referring to some other pagetable.  The only
other use of pud_clear is during a large (1Gbyte+) munmap, and those
are sufficiently rare that a couple of cr3 reloads won't hurt.

Signed-off-by: Jeremy Fitzhardinge <jeremy@xensource.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
This commit is contained in:
Jeremy Fitzhardinge 2008-02-04 16:48:02 +01:00 committed by Ingo Molnar
parent a67ad9c9f8
commit edd6bcd820
1 changed files with 7 additions and 4 deletions
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11
include/asm-x86/pgtable-3level.h
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@ -93,17 +93,20 @@ static inline void native_pmd_clear(pmd_t *pmd)
static inline void pud_clear(pud_t *pudp)
{
unsigned long pgd;
set_pud(pudp, __pud(0));
/*
* Pentium-II erratum A13: in PAE mode we explicitly have to flush
* the TLB via cr3 if the top-level pgd is changed...
*
* 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
* Make sure the pud entry we're updating is within the
* current pgd to avoid unnecessary TLB flushes.
*/
write_cr3(read_cr3());
pgd = read_cr3();
if (__pa(pudp) >= pgd && __pa(pudp) < (pgd + sizeof(pgd_t)*PTRS_PER_PGD))
write_cr3(pgd);
}
#define pud_page(pud) \