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powerpc/64s: add pte_needs_flush and huge_pmd_needs_flush

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Allow PTE changes to avoid flushing the TLB when access permissions are
being relaxed, the dirty bit is being set, and the accessed bit is being
changed.

Relaxing access permissions and setting dirty and accessed bits do not
require a flush because the MMU will re-load the PTE and notice the
updates (it may also cause a spurious fault).

Clearing the accessed bit does not require a flush because of the
imprecise PTE accessed bit accounting that is already performed, as
documented in ptep_clear_flush_young().

This reduces TLB flushing for some mprotect(2) calls.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Reviewed-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Link: https://lore.kernel.org/r/20220901110334.1618913-1-npiggin@gmail.com
This commit is contained in:
Nicholas Piggin
2022-09-01 21:03:34 +10:00
committed by Michael Ellerman
parent 78c73c80fd
commit b11931e9ad
2 changed files with 59 additions and 0 deletions
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3
arch/powerpc/include/asm/book3s/64/pgtable.h
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@@ -413,6 +413,9 @@ static inline int __ptep_test_and_clear_young(struct mm_struct *mm,
* event of it not getting flushed for a long time the delay
* shouldn't really matter because there's no real memory
* pressure for swapout to react to. ]
*
* Note: this optimisation also exists in pte_needs_flush() and
* huge_pmd_needs_flush().
*/
#define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
#define ptep_clear_flush_young ptep_test_and_clear_young