linux-kernel - [PATCH 1/5] KVM: nVMX: Invoke ept_save_pdptrs() if and only if PAE paging is enabled

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Message-Id: <20200415203454.8296-2-sean.j.christopherson@intel.com>
Date:   Wed, 15 Apr 2020 13:34:50 -0700
From:   Sean Christopherson <sean.j.christopherson@...el.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <sean.j.christopherson@...el.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 1/5] KVM: nVMX: Invoke ept_save_pdptrs() if and only if PAE paging is enabled

Invoke ept_save_pdptrs() when restoring L1's host state on a "late"
VM-Fail if and only if PAE paging is enabled.  This saves a CALL in the
common case where L1 is a 64-bit host, and avoids incorrectly marking
the PDPTRs as dirty.

WARN if ept_save_pdptrs() is called with PAE disabled now that the
nested usage pre-checks is_pae_paging().  Barring a bug in KVM's MMU,
attempting to read the PDPTRs with PAE disabled is now impossible.

Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
---
 arch/x86/kvm/vmx/nested.c |  2 +-
 arch/x86/kvm/vmx/vmx.c    | 13 +++++++------
 2 files changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index aca57d8da400..f9ae42209d78 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -4250,7 +4250,7 @@ static void nested_vmx_restore_host_state(struct kvm_vcpu *vcpu)
 	 * VMFail, like everything else we just need to ensure our
 	 * software model is up-to-date.
 	 */
-	if (enable_ept)
+	if (enable_ept && is_pae_paging(vcpu))
 		ept_save_pdptrs(vcpu);
 
 	kvm_mmu_reset_context(vcpu);
diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index aa1b8cf7c915..7da83325ace3 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -2937,12 +2937,13 @@ void ept_save_pdptrs(struct kvm_vcpu *vcpu)
 {
 	struct kvm_mmu *mmu = vcpu->arch.walk_mmu;
 
-	if (is_pae_paging(vcpu)) {
-		mmu->pdptrs[0] = vmcs_read64(GUEST_PDPTR0);
-		mmu->pdptrs[1] = vmcs_read64(GUEST_PDPTR1);
-		mmu->pdptrs[2] = vmcs_read64(GUEST_PDPTR2);
-		mmu->pdptrs[3] = vmcs_read64(GUEST_PDPTR3);
-	}
+	if (WARN_ON_ONCE(!is_pae_paging(vcpu)))
+		return;
+
+	mmu->pdptrs[0] = vmcs_read64(GUEST_PDPTR0);
+	mmu->pdptrs[1] = vmcs_read64(GUEST_PDPTR1);
+	mmu->pdptrs[2] = vmcs_read64(GUEST_PDPTR2);
+	mmu->pdptrs[3] = vmcs_read64(GUEST_PDPTR3);
 
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
 }
-- 
2.26.0