From 908e7d7999bcce70ac52e7f390a8f5cbc55948de Mon Sep 17 00:00:00 2001 From: Gleb Natapov Date: Thu, 27 Dec 2012 14:44:58 +0200 Subject: [PATCH] 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 Signed-off-by: Marcelo Tosatti --- arch/x86/kvm/paging_tmpl.h | 16 ++++++---------- 1 file changed, 6 insertions(+), 10 deletions(-) diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h index 891eb6d..a7b24cf 100644 --- a/arch/x86/kvm/paging_tmpl.h +++ b/arch/x86/kvm/paging_tmpl.h @@ -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); -- 2.7.4