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

[Lai Jiangshan]

From: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>

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@xxxxxxxxxx>
Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxxxxx>
---
 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