From: Sean Christopherson <seanjc@google.com>
To: Paolo Bonzini <pbonzini@redhat.com>
Cc: Sean Christopherson <seanjc@google.com>,
Vitaly Kuznetsov <vkuznets@redhat.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>, Joerg Roedel <joro@8bytes.org>,
kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH 2/4] KVM: nSVM: Drop pointless pdptrs_changed() check on nested transition
Date: Thu, 22 Apr 2021 17:06:35 -0700 [thread overview]
Message-ID: <20210423000637.3692951-3-seanjc@google.com> (raw)
In-Reply-To: <20210423000637.3692951-1-seanjc@google.com>
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@google.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
next prev parent reply other threads:[~2021-04-23 0:06 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-23 0:06 [PATCH 0/4] KVM: x86: Kill off pdptrs_changed() Sean Christopherson
2021-04-23 0:06 ` [PATCH 1/4] KVM: nVMX: Drop obsolete (and pointless) pdptrs_changed() check Sean Christopherson
2021-04-23 0:06 ` Sean Christopherson [this message]
2021-04-23 0:06 ` [PATCH 3/4] KVM: x86: Always load PDPTRs on CR3 load for SVM w/o NPT and a PAE guest Sean Christopherson
2021-04-23 0:06 ` [PATCH 4/4] KVM: x86: Unexport kvm_read_guest_page_mmu() Sean Christopherson
2021-04-23 7:04 ` [PATCH 0/4] KVM: x86: Kill off pdptrs_changed() Paolo Bonzini
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