linux-kernel - [PATCH v3 8/8] KVM: x86: avoid loading PDPTRs after migration when possible

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Message-Id: <20210607090203.133058-9-mlevitsk@redhat.com>
Date:   Mon,  7 Jun 2021 12:02:03 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        linux-kernel@...r.kernel.org (open list),
        linux-doc@...r.kernel.org (open list:DOCUMENTATION),
        Wanpeng Li <wanpengli@...cent.com>,
        Ingo Molnar <mingo@...hat.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>, Joerg Roedel <joro@...tes.org>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Jim Mattson <jmattson@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        "H. Peter Anvin" <hpa@...or.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH v3 8/8] KVM: x86: avoid loading PDPTRs after migration when possible

if new KVM_*_SREGS2 ioctls are used, the PDPTRs are
a part of the migration state and are correctly
restored by those ioctls.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/include/asm/kvm_host.h | 6 ++++++
 arch/x86/kvm/svm/nested.c       | 3 ++-
 arch/x86/kvm/vmx/nested.c       | 3 ++-
 arch/x86/kvm/x86.c              | 3 +++
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 83f948bdc59a..8eb107ceb45a 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -851,6 +851,12 @@ struct kvm_vcpu_arch {
 
 	/* Protected Guests */
 	bool guest_state_protected;
+
+	/*
+	 * Set when PDPTS were loaded directly by the userspace without
+	 * reading the guest memory
+	 */
+	bool pdptrs_restored_oob;
 };
 
 struct kvm_lpage_info {
diff --git a/arch/x86/kvm/svm/nested.c b/arch/x86/kvm/svm/nested.c
index e3e5775b8f1c..0f80d68a45e1 100644
--- a/arch/x86/kvm/svm/nested.c
+++ b/arch/x86/kvm/svm/nested.c
@@ -1369,7 +1369,8 @@ static bool svm_get_nested_state_pages(struct kvm_vcpu *vcpu)
 	if (WARN_ON(!is_guest_mode(vcpu)))
 		return true;
 
-	if (!nested_npt_enabled(svm) && is_pae_paging(vcpu))
+	if (!vcpu->arch.pdptrs_restored_oob &&
+	    !nested_npt_enabled(svm) && is_pae_paging(vcpu))
 		/*
 		 * Reload the guest's PDPTRs since after a migration
 		 * the guest CR3 might be restored prior to setting the nested
diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 0acdda85f36a..78d6c71ab03b 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3113,7 +3113,8 @@ static bool nested_get_vmcs12_pages(struct kvm_vcpu *vcpu)
 	struct page *page;
 	u64 hpa;
 
-	if (!nested_cpu_has_ept(vmcs12) && is_pae_paging(vcpu)) {
+	if (!vcpu->arch.pdptrs_restored_oob &&
+	    !nested_cpu_has_ept(vmcs12) && is_pae_paging(vcpu)) {
 		/*
 		 * Reload the guest's PDPTRs since after a migration
 		 * the guest CR3 might be restored prior to setting the nested
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 11260e83518f..eadfc9caf500 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -815,6 +815,8 @@ int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3)
 
 	memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
+	vcpu->arch.pdptrs_restored_oob = false;
+
 out:
 
 	return ret;
@@ -10113,6 +10115,7 @@ static int __set_sregs2(struct kvm_vcpu *vcpu, struct kvm_sregs2 *sregs2)
 
 		kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
 		mmu_reset_needed = 1;
+		vcpu->arch.pdptrs_restored_oob = true;
 	}
 	if (mmu_reset_needed)
 		kvm_mmu_reset_context(vcpu);
-- 
2.26.3