linux-kernel - [PATCH v2 6/7] KVM: nVMX: Request to sync eVMCS from VMCS12 after migration

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Message-Id: <20210517135054.1914802-7-vkuznets@redhat.com>
Date:   Mon, 17 May 2021 15:50:53 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        linux-kernel@...r.kernel.org
Subject: [PATCH v2 6/7] KVM: nVMX: Request to sync eVMCS from VMCS12 after migration

VMCS12 is used to keep the authoritative state during nested state
migration. In case 'need_vmcs12_to_shadow_sync' flag is set, we're
in between L2->L1 vmexit and L1 guest run when actual sync to
enlightened (or shadow) VMCS happens. Nested state, however, has
no flag for 'need_vmcs12_to_shadow_sync' so vmx_set_nested_state()->
set_current_vmptr() always sets it. Enlightened vmptrld path, however,
doesn't have the quirk so some VMCS12 changes may not get properly
reflected to eVMCS and L1 will see an incorrect state.

Note, during L2 execution or when need_vmcs12_to_shadow_sync is not
set the change is effectively a nop: in the former case all changes
will get reflected during the first L2->L1 vmexit and in the later
case VMCS12 and eVMCS are already in sync (thanks to
copy_enlightened_to_vmcs12() in vmx_get_nested_state()).

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3bfbf991bf45..a0dedd413a23 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -3127,6 +3127,12 @@ static bool nested_get_evmcs_page(struct kvm_vcpu *vcpu)
 		if (evmptrld_status == EVMPTRLD_VMFAIL ||
 		    evmptrld_status == EVMPTRLD_ERROR)
 			return false;
+
+		/*
+		 * Post migration VMCS12 always provides the most actual
+		 * information, copy it to eVMCS upon entry.
+		 */
+		vmx->nested.need_vmcs12_to_shadow_sync = true;
 	}

 	return true;
-- 
2.31.1