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    SubjectRe: [PATCH v3] x86/sgx: Synchronize encl->srcu in sgx_encl_release().
    Date
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    On Wed, 16 Dec 2020 07:49:20 -0600, Jarkko Sakkinen <jarkko@kernel.org>  
    wrote:

    > Add synchronize_srcu_expedited() to sgx_encl_release() to catch a grace
    > period initiated by sgx_mmu_notifier_release().
    >
    > A trivial example of a failing sequence with tasks A and B:
    >
    > 1. A: -> sgx_release()
    > 2. B: -> sgx_mmu_notifier_release()
    > 3. B: -> list_del_rcu()
    > 3. A: -> sgx_encl_release()
    > 4. A: -> cleanup_srcu_struct()
    >
    > The loop in sgx_release() observes an empty list because B has removed
    > its
    > entry in the middle, and calls cleanup_srcu_struct() before B has a
    > chance
    > to calls synchronize_srcu().
    >
    > Fixes: 1728ab54b4be ("x86/sgx: Add a page reclaimer")
    > Suggested-by: Sean Christopherson <seanjc@google.com>
    > Suggested-by: Haitao Huang <haitao.huang@linux.intel.com>
    > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
    > ---
    > v3: Fine-tuned tags, and added missing change log for v2.
    > v2: Switch to synchronize_srcu_expedited().
    > arch/x86/kernel/cpu/sgx/encl.c | 6 ++++++
    > 1 file changed, 6 insertions(+)
    >
    > diff --git a/arch/x86/kernel/cpu/sgx/encl.c
    > b/arch/x86/kernel/cpu/sgx/encl.c
    > index ee50a5010277..fe7256db6e73 100644
    > --- a/arch/x86/kernel/cpu/sgx/encl.c
    > +++ b/arch/x86/kernel/cpu/sgx/encl.c
    > @@ -438,6 +438,12 @@ void sgx_encl_release(struct kref *ref)
    > if (encl->backing)
    > fput(encl->backing);
    > + /*
    > + * Each sgx_mmu_notifier_release() starts a grace period. Therefore, an
    > + * additional sync is required here.
    > + */
    > + synchronize_srcu_expedited(&encl->srcu);
    > +
    > cleanup_srcu_struct(&encl->srcu);
    > WARN_ON_ONCE(!list_empty(&encl->mm_list));

    Tested-by: Haitao Huang <haitao.huang@linux.intel.com>
    Thanks
    Haitao

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