linux-kernel - [PATCH v3 3/7] KVM: x86: reset pdptrs_from

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Date:   Mon, 13 Sep 2021 17:09:50 +0300
From:   Maxim Levitsky <mlevitsk@...hat.com>
To:     kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>, linux-kernel@...r.kernel.org,
        Jim Mattson <jmattson@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Borislav Petkov <bp@...en8.de>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Maxim Levitsky <mlevitsk@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        x86@...nel.org (maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)),
        Joerg Roedel <joro@...tes.org>
Subject: [PATCH v3 3/7] KVM: x86: reset pdptrs_from_userspace when exiting smm

When exiting SMM, pdpts are loaded again from the guest memory.

This fixes a theoretical bug, when exit from SMM triggers entry to the
nested guest which re-uses some of the migration
code which uses this flag as a workaround for a legacy userspace.

Signed-off-by: Maxim Levitsky <mlevitsk@...hat.com>
---
 arch/x86/kvm/x86.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 86539c1686fa..3a61f19455cb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -7654,6 +7654,13 @@ static void kvm_smm_changed(struct kvm_vcpu *vcpu, bool entering_smm)
 
 		/* Process a latched INIT or SMI, if any.  */
 		kvm_make_request(KVM_REQ_EVENT, vcpu);
+
+		/*
+		 * Even if KVM_SET_SREGS2 loaded PDPTRs out of band,
+		 * on SMM exit we still need to reload them from
+		 * guest memory
+		 */
+		vcpu->arch.pdptrs_from_userspace = false;
 	}
 
 	kvm_mmu_reset_context(vcpu);
-- 
2.26.3