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    Subject[PATCH 29/46] KVM: MMU: fix missing locking in alloc_mmu_pages
    Date
    From: Marcelo Tosatti <mtosatti@redhat.com>

    n_requested_mmu_pages/n_free_mmu_pages are used by
    kvm_mmu_change_mmu_pages to calculate the number of pages to zap.

    alloc_mmu_pages, called from the vcpu initialization path, modifies this
    variables without proper locking, which can result in a negative value
    in kvm_mmu_change_mmu_pages (say, with cpu hotplug).

    Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
    ---
    arch/x86/kvm/mmu.c | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
    index 87c67f4..86c2551 100644
    --- a/arch/x86/kvm/mmu.c
    +++ b/arch/x86/kvm/mmu.c
    @@ -2728,12 +2728,14 @@ static int alloc_mmu_pages(struct kvm_vcpu *vcpu)

    ASSERT(vcpu);

    + spin_lock(&vcpu->kvm->mmu_lock);
    if (vcpu->kvm->arch.n_requested_mmu_pages)
    vcpu->kvm->arch.n_free_mmu_pages =
    vcpu->kvm->arch.n_requested_mmu_pages;
    else
    vcpu->kvm->arch.n_free_mmu_pages =
    vcpu->kvm->arch.n_alloc_mmu_pages;
    + spin_unlock(&vcpu->kvm->mmu_lock);
    /*
    * When emulating 32-bit mode, cr3 is only 32 bits even on x86_64.
    * Therefore we need to allocate shadow page tables in the first
    --
    1.6.4.1


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