linux-kernel - [PATCH 2/4] KVM: nSVM: Drop pointless pdptrs

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Message-Id: <20210423000637.3692951-3-seanjc@google.com>
Date:   Thu, 22 Apr 2021 17:06:35 -0700
From:   Sean Christopherson <seanjc@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH 2/4] KVM: nSVM: Drop pointless pdptrs_changed() check on
 nested transition

Remove the "PDPTRs unchanged" check to skip PDPTR loading during nested
SVM transitions as it's not at all an optimization.  Reading guest memory
to get the PDPTRs isn't magically cheaper by doing it in pdptrs_changed(),
and if the PDPTRs did change, KVM will end up doing the read twice.

Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/nested.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index 540d43ba2cf4..9cc95895866a 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -391,10 +391,8 @@ static int nested_svm_load_cr3(struct kvm_vcpu *vcpu, unsigned long cr3,
 		return -EINVAL;
 
 	if (!nested_npt && is_pae_paging(vcpu) &&
-	    (cr3 != kvm_read_cr3(vcpu) || pdptrs_changed(vcpu))) {
-		if (CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)))
-			return -EINVAL;
-	}
+	    CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)))
+		return -EINVAL;
 
 	/*
 	 * TODO: optimize unconditional TLB flush/MMU sync here and in
-- 
2.31.1.498.g6c1eba8ee3d-goog