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KVM: MMU: simplify folding of dirty bit into accessed_dirty 

MMU code tries to avoid if()s HW is not able to predict reliably by using
bitwise operation to streamline code execution, but in case of a dirty bit
folding this gives us nothing since write_fault is checked right before
the folding code. Lets just piggyback onto the if() to make code more clear.

Signed-off-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
This commit is contained in:
Gleb Natapov 2012-12-27 14:44:58 +02:00 committed by Marcelo Tosatti
parent ee04e0cea8
commit 908e7d7999
1 changed files with 6 additions and 10 deletions
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16
arch/x86/kvm/paging_tmpl.h
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@ -249,16 +249,12 @@ retry_walk:
if (!write_fault)
protect_clean_gpte(&pte_access, pte);
/*
* On a write fault, fold the dirty bit into accessed_dirty by shifting it one
* place right.
*
* On a read fault, do nothing.
*/
shift = write_fault >> ilog2(PFERR_WRITE_MASK);
shift *= PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT;
accessed_dirty &= pte >> shift;
else
/*
* On a write fault, fold the dirty bit into accessed_dirty by
* shifting it one place right.
*/
accessed_dirty &= pte >> (PT_DIRTY_SHIFT - PT_ACCESSED_SHIFT);
if (unlikely(!accessed_dirty)) {
ret = FNAME(update_accessed_dirty_bits)(vcpu, mmu, walker, write_fault);