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