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[PATCH] paravirt: optimize ptep establish for pae
The ptep_establish macro is only used on user-level PTEs, for P->P mapping changes. Since these always happen under protection of the pagetable lock, the strong synchronization of a 64-bit cmpxchg is not needed, in fact, not even a lock prefix needs to be used. We can simply instead clear the P-bit, followed by a normal set. The write ordering is still important to avoid the possibility of the TLB snooping a partially written PTE and getting a bad mapping installed. Signed-off-by: Zachary Amsden <zach@vmware.com> Cc: Rusty Russell <rusty@rustcorp.com.au> Cc: Jeremy Fitzhardinge <jeremy@xensource.com> Cc: Andi Kleen <ak@suse.de> Signed-off-by: Andrew Morton <akpm@osdl.org> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
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@ -16,6 +16,7 @@
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#define set_pte(pteptr, pteval) (*(pteptr) = pteval)
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#define set_pte_at(mm,addr,ptep,pteval) set_pte(ptep,pteval)
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#define set_pte_atomic(pteptr, pteval) set_pte(pteptr,pteval)
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#define set_pte_present(mm,addr,ptep,pteval) set_pte_at(mm,addr,ptep,pteval)
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#define set_pmd(pmdptr, pmdval) (*(pmdptr) = (pmdval))
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#define pte_clear(mm,addr,xp) do { set_pte_at(mm, addr, xp, __pte(0)); } while (0)
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@ -58,6 +58,21 @@ static inline void set_pte(pte_t *ptep, pte_t pte)
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}
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#define set_pte_at(mm,addr,ptep,pteval) set_pte(ptep,pteval)
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/*
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* Since this is only called on user PTEs, and the page fault handler
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* must handle the already racy situation of simultaneous page faults,
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* we are justified in merely clearing the PTE present bit, followed
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* by a set. The ordering here is important.
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*/
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static inline void set_pte_present(struct mm_struct *mm, unsigned long addr, pte_t *ptep, pte_t pte)
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{
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ptep->pte_low = 0;
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smp_wmb();
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ptep->pte_high = pte.pte_high;
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smp_wmb();
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ptep->pte_low = pte.pte_low;
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}
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#define __HAVE_ARCH_SET_PTE_ATOMIC
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#define set_pte_atomic(pteptr,pteval) \
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set_64bit((unsigned long long *)(pteptr),pte_val(pteval))
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@ -269,6 +269,17 @@ do { \
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#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_DIRTY
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#define __HAVE_ARCH_PTEP_TEST_AND_CLEAR_YOUNG
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/*
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* Rules for using ptep_establish: the pte MUST be a user pte, and
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* must be a present->present transition.
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*/
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#define __HAVE_ARCH_PTEP_ESTABLISH
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#define ptep_establish(vma, address, ptep, pteval) \
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do { \
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set_pte_present((vma)->vm_mm, address, ptep, pteval); \
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flush_tlb_page(vma, address); \
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} while (0)
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#define __HAVE_ARCH_PTEP_CLEAR_DIRTY_FLUSH
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#define ptep_clear_flush_dirty(vma, address, ptep) \
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({ \
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