linux-kernel - [PATCH V2 2/3] KVM: x86/mmu: Ensure pae_root to be reconstructed for shadow paging if the guest PDPTEs is changed

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Date:   Thu, 16 Dec 2021 10:19:37 +0800
From:   Lai Jiangshan <jiangshanlai@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Maxim Levitsky <mlevitsk@...hat.com>
Cc:     Lai Jiangshan <laijs@...ux.alibaba.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Xiao Guangrong <guangrong.xiao@...ux.intel.com>
Subject: [PATCH V2 2/3] KVM: x86/mmu: Ensure pae_root to be reconstructed for shadow paging if the guest PDPTEs is changed

From: Lai Jiangshan <laijs@...ux.alibaba.com>

For shadow paging, the pae_root needs to be reconstructed before the
coming VMENTER if the guest PDPTEs is changed.

But not all paths that call load_pdptrs() will cause the pae_root to be
reconstructed. Normally, kvm_mmu_reset_context() and kvm_mmu_free_roots()
are used to launch later reconstruction.

The commit d81135a57aa6("KVM: x86: do not reset mmu if CR0.CD and
CR0.NW are changed") skips kvm_mmu_reset_context() after load_pdptrs()
when changing CR0.CD and CR0.NW.

The commit 21823fbda552("KVM: x86: Invalidate all PGDs for the current
PCID on MOV CR3 w/ flush") skips kvm_mmu_free_roots() after
load_pdptrs() when rewriting the CR3 with the same value.

The commit a91a7c709600("KVM: X86: Don't reset mmu context when
toggling X86_CR4_PGE") skips kvm_mmu_reset_context() after
load_pdptrs() when changing CR4.PGE.

Guests like linux would keep the PDPTEs unchanged for every instance of
pagetable, so this missing reconstruction has no problem for linux
guests.

Fixes: d81135a57aa6("KVM: x86: do not reset mmu if CR0.CD and CR0.NW are changed")
Fixes: 21823fbda552("KVM: x86: Invalidate all PGDs for the current PCID on MOV CR3 w/ flush")
Fixes: a91a7c709600("KVM: X86: Don't reset mmu context when toggling X86_CR4_PGE")
Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Lai Jiangshan <laijs@...ux.alibaba.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 af22ad79e081..71c389a47801 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -841,6 +841,13 @@ int load_pdptrs(struct kvm_vcpu *vcpu, unsigned long cr3)
 		}
 	}

+	/*
+	 * Marking VCPU_EXREG_PDPTR dirty doesn't work for !tdp_enabled.
+	 * Shadow page roots need to be reconstructed instead.
+	 */
+	if (!tdp_enabled && memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs)))
+		kvm_mmu_free_roots(vcpu, mmu, KVM_MMU_ROOT_CURRENT);
+
 	memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
 	kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
 	kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
-- 
2.19.1.6.gb485710b