linux-kernel - [PATCH 5/7] KVM: nVMX: Reset eVMCS clean fields data from prepare

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Date:   Tue, 11 May 2021 13:19:54 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kvm@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org,
        Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Subject: [PATCH 5/7] KVM: nVMX: Reset eVMCS clean fields data from prepare_vmcs02()

When nested state migration happens during L1's execution, it
is incorrect to modify eVMCS as it is L1 who 'owns' it at the moment.
At lease genuine Hyper-v seems to not be very happy when 'clean fields'
data changes underneath it.

'Clean fields' data is used in KVM twice: by copy_enlightened_to_vmcs12()
and prepare_vmcs02_rare() so we can reset it from prepare_vmcs02() instead.

Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
---
 arch/x86/kvm/vmx/nested.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/vmx/nested.c b/arch/x86/kvm/vmx/nested.c
index 3257a2291693..1661e2e19560 100644
--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -2090,9 +2090,6 @@ void nested_sync_vmcs12_to_shadow(struct kvm_vcpu *vcpu)
 
 	if (vmx->nested.hv_evmcs) {
 		copy_vmcs12_to_enlightened(vmx);
-		/* All fields are clean */
-		vmx->nested.hv_evmcs->hv_clean_fields |=
-			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
 	} else {
 		copy_vmcs12_to_shadow(vmx);
 	}
@@ -2636,6 +2633,12 @@ static int prepare_vmcs02(struct kvm_vcpu *vcpu, struct vmcs12 *vmcs12,
 
 	kvm_rsp_write(vcpu, vmcs12->guest_rsp);
 	kvm_rip_write(vcpu, vmcs12->guest_rip);
+
+	/* Mark all fields as clean so L1 hypervisor can set what's dirty */
+	if (hv_evmcs)
+		vmx->nested.hv_evmcs->hv_clean_fields |=
+			HV_VMX_ENLIGHTENED_CLEAN_FIELD_ALL;
+
 	return 0;
 }
 
-- 
2.30.2