linux-kernel - [PATCH 9/9] x86/kvm/mmu: check if MMU reconfiguration is needed in init_kvm_nested

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Date:   Thu,  2 Aug 2018 12:01:32 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, Jim Mattson <jmattson@...gle.com>,
        Liran Alon <liran.alon@...cle.com>
Subject: [PATCH 9/9] x86/kvm/mmu: check if MMU reconfiguration is needed in init_kvm_nested_mmu()

We don't use root page role for nested_mmu, however, optimizing out
re-initialization in case nothing changed is still valuable as this
is done for every nested vmentry.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/mmu.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index c621d9892a37..3d57c3961765 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -4877,8 +4877,14 @@ static void init_kvm_softmmu(struct kvm_vcpu *vcpu)
 
 static void init_kvm_nested_mmu(struct kvm_vcpu *vcpu)
 {
+	union kvm_mmu_role new_role = kvm_calc_mmu_role_common(vcpu, true);
 	struct kvm_mmu *g_context = &vcpu->arch.nested_mmu;
 
+	new_role.base_role.word &= mmu_base_role_mask.word;
+	if (new_role.as_u64 == g_context->mmu_role.as_u64)
+		return;
+
+	g_context->mmu_role.as_u64 = new_role.as_u64;
 	g_context->get_cr3           = get_cr3;
 	g_context->get_pdptr         = kvm_pdptr_read;
 	g_context->inject_page_fault = kvm_inject_page_fault;
-- 
2.14.4