linux-kernel - [PATCH 5/6] KVM: nSVM: avoid loading PDPTRs after migration when possible

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Date:   Thu,  1 Apr 2021 17:18:13 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Jim Mattson <jmattson@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-kernel@...r.kernel.org (open list:X86 ARCHITECTURE (32-BIT AND
        64-BIT)), Paolo Bonzini <pbonzini@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jonathan Corbet <corbet@....net>,
        Borislav Petkov <bp@...en8.de>, Ingo Molnar <mingo@...hat.com>,
        linux-doc@...r.kernel.org (open list:DOCUMENTATION),
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 5/6] KVM: nSVM: avoid loading PDPTRs after migration when possible

if new KVM_*_SREGS2 ioctls are used, the PDPTRs are
part of the migration state and thus are loaded
by those ioctls.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/svm/nested.c | 15 +++++++++++++--
 1 file changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index ac5e3e17bda4..b94916548cfa 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -373,10 +373,9 @@ 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))) {
+	    (cr3 != kvm_read_cr3(vcpu) || !kvm_register_is_available(vcpu, VCPU_EXREG_PDPTR)))
 		if (CC(!load_pdptrs(vcpu, vcpu->arch.walk_mmu, cr3)))
 			return -EINVAL;
-	}
 
 	/*
 	 * TODO: optimize unconditional TLB flush/MMU sync here and in
@@ -552,6 +551,8 @@ int enter_svm_guest_mode(struct kvm_vcpu *vcpu, u64 vmcb12_gpa,
 	nested_vmcb02_prepare_control(svm);
 	nested_vmcb02_prepare_save(svm, vmcb12);
 
+	kvm_register_clear_available(&svm->vcpu, VCPU_EXREG_PDPTR);
+
 	ret = nested_svm_load_cr3(&svm->vcpu, vmcb12->save.cr3,
 				  nested_npt_enabled(svm));
 	if (ret)
@@ -779,6 +780,8 @@ int nested_svm_vmexit(struct vcpu_svm *svm)
 
 	nested_svm_uninit_mmu_context(vcpu);
 
+	kvm_register_clear_available(&svm->vcpu, VCPU_EXREG_PDPTR);
+
 	rc = nested_svm_load_cr3(vcpu, svm->vmcb->save.cr3, false);
 	if (rc)
 		return 1;
@@ -1301,6 +1304,14 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 	if (WARN_ON(!is_guest_mode(vcpu)))
 		return true;
 
+	if (vcpu->arch.reload_pdptrs_on_nested_entry) {
+		/* If legacy KVM_SET_SREGS API was used, it might have
+		 * loaded wrong PDPTRs from memory so we have to reload
+		 * them here (which is against x86 spec)
+		 */
+		kvm_register_clear_available(vcpu, VCPU_EXREG_PDPTR);
+	}
+
 	if (nested_svm_load_cr3(&svm->vcpu, vcpu->arch.cr3,
 				nested_npt_enabled(svm)))
 		return false;
-- 
2.26.2