linux-kernel - [PATCH 2/5] KVM: x86: MMU: Simplify force_pt_level calculation code in FNAME(page

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Message-Id: <20151016170513.6ec5ad9c360aad4ac63b0a16@lab.ntt.co.jp>
Date:	Fri, 16 Oct 2015 17:05:13 +0900
From:	Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
To:	pbonzini@...hat.com
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 2/5] KVM: x86: MMU: Simplify force_pt_level calculation code
 in FNAME(page_fault)()

As a bonus, an extra memory slot search can be eliminated when
is_self_change_mapping is true.

Signed-off-by: Takuya Yoshikawa <yoshikawa_takuya_b1@....ntt.co.jp>
---
 arch/x86/kvm/paging_tmpl.h | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

diff --git a/arch/x86/kvm/paging_tmpl.h b/arch/x86/kvm/paging_tmpl.h
index 07f1a4e..8ebc3a5 100644
--- a/arch/x86/kvm/paging_tmpl.h
+++ b/arch/x86/kvm/paging_tmpl.h
@@ -743,15 +743,14 @@ static int FNAME(page_fault)(struct kvm_vcpu *vcpu, gva_t addr, u32 error_code,
 	is_self_change_mapping = FNAME(is_self_change_mapping)(vcpu,
 	      &walker, user_fault, &vcpu->arch.write_fault_to_shadow_pgtable);
 
-	if (walker.level >= PT_DIRECTORY_LEVEL)
-		force_pt_level = mapping_level_dirty_bitmap(vcpu, walker.gfn)
-		   || is_self_change_mapping;
-	else
+	if (walker.level >= PT_DIRECTORY_LEVEL && !is_self_change_mapping) {
+		force_pt_level = mapping_level_dirty_bitmap(vcpu, walker.gfn);
+		if (!force_pt_level) {
+			level = min(walker.level, mapping_level(vcpu, walker.gfn));
+			walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
+		}
+	} else
 		force_pt_level = true;
-	if (!force_pt_level) {
-		level = min(walker.level, mapping_level(vcpu, walker.gfn));
-		walker.gfn = walker.gfn & ~(KVM_PAGES_PER_HPAGE(level) - 1);
-	}
 
 	mmu_seq = vcpu->kvm->mmu_notifier_seq;
 	smp_rmb();
-- 
2.1.0

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