[PATCH 17/15] KVM: X86: Ensure pae_root to be reconstructed for shadow paging if the guest PDPTEs is changed

Lai Jiangshan
2021-11-11T14:46:29Z

From: Lai Jiangshan <laijs@linux.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.

Normally, the guest doesn't change the PDPTEs before doing only the
above operation without touching other bits that can force pae_root to
be reconstructed. Guests like linux would keep the PDPTEs unchaged
for every instance of pagetable.

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")
Signed-off-by: Lai Jiangshan <laijs@linux.alibaba.com>
---
arch/x86/kvm/x86.c | 10 ++++++++--
1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0176eaa86a35..cfba337e46ab 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -832,8 +832,14 @@ int load_pdptrs(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu, unsigned long cr3)
if (memcmp(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs))) {
memcpy(mmu->pdptrs, pdpte, sizeof(mmu->pdptrs));
kvm_register_mark_dirty(vcpu, VCPU_EXREG_PDPTR);
- /* Ensure the dirty PDPTEs to be loaded. */
- kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
+ /*
+ * Ensure the dirty PDPTEs to be loaded for VMX with EPT
+ * enabled or pae_root to be reconstructed for shadow paging.
+ */
+ if (tdp_enabled)
+ kvm_make_request(KVM_REQ_LOAD_MMU_PGD, vcpu);
+ else
+ kvm_mmu_free_roots(vcpu, vcpu->arch.mmu, KVM_MMU_ROOT_CURRENT);
}
vcpu->arch.pdptrs_from_userspace = false;

--
2.19.1.6.gb485710b