linux-kernel - [PATCH 5.12 118/677] KVM: nVMX: Defer the MMU reload to the normal path on an EPTP switch

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Message-Id: <20210512144841.127846235@linuxfoundation.org>
Date:   Wed, 12 May 2021 16:42:44 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Sean Christopherson <seanjc@...gle.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: [PATCH 5.12 118/677] KVM: nVMX: Defer the MMU reload to the normal path on an EPTP switch

From: Sean Christopherson <seanjc@...gle.com>

commit c805f5d5585ab5e0cdac6b1ccf7086eb120fb7db upstream.

Defer reloading the MMU after a EPTP successful EPTP switch.  The VMFUNC
instruction itself is executed in the previous EPTP context, any side
effects, e.g. updating RIP, should occur in the old context.  Practically
speaking, this bug is benign as VMX doesn't touch the MMU when skipping
an emulated instruction, nor does queuing a single-step #DB.  No other
post-switch side effects exist.

Fixes: 41ab93727467 ("KVM: nVMX: Emulate EPTP switching for the L1 hypervisor")
Cc: stable@...r.kernel.org
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Message-Id: <20210305011101.3597423-14-seanjc@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/vmx/nested.c |    9 ++-------
 1 file changed, 2 insertions(+), 7 deletions(-)

--- a/arch/x86/kvm/vmx/nested.c
+++ b/arch/x86/kvm/vmx/nested.c
@@ -5479,16 +5479,11 @@ static int nested_vmx_eptp_switching(str
 		if (!nested_vmx_check_eptp(vcpu, new_eptp))
 			return 1;
 
-		kvm_mmu_unload(vcpu);
 		mmu->ept_ad = accessed_dirty;
 		mmu->mmu_role.base.ad_disabled = !accessed_dirty;
 		vmcs12->ept_pointer = new_eptp;
-		/*
-		 * TODO: Check what's the correct approach in case
-		 * mmu reload fails. Currently, we just let the next
-		 * reload potentially fail
-		 */
-		kvm_mmu_reload(vcpu);
+
+		kvm_make_request(KVM_REQ_MMU_RELOAD, vcpu);
 	}
 
 	return 0;