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    SubjectRe: [PATCH v5 12/18] x86/sgx: Add EPC OOM path to forcefully reclaim EPC
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    Hi Sean

    On Mon, 16 Oct 2023 16:32:31 -0500, Sean Christopherson
    <seanjc@google.com> wrote:

    > On Mon, Oct 16, 2023, Haitao Huang wrote:
    >> From this perspective, I think the current implementation is
    >> "well-defined":
    >> EPC cgroup limits for VMs are only enforced at VM launch time, not
    >> runtime.
    >> In practice, SGX VM can be launched only with fixed EPC size and all
    >> those
    >> EPCs are fully committed to the VM once launched.
    >
    > Fully committed doesn't mean those numbers are reflected in the cgroup.
    > A VM
    > scheduler can easily "commit" EPC to a guest, but allocate EPC on
    > demand, i.e.
    > when the guest attempts to actually access a page. Preallocating memory
    > isn't
    > free, e.g. it can slow down guest boot, so it's entirely reasonable to
    > have virtual
    > EPC be allocated on-demand. Enforcing at launch time doesn't work for
    > such setups,
    > because from the cgroup's perspective, the VM is using 0 pages of EPC at
    > launch.
    >
    Maybe I understood the current implementation wrong. From what I see, vEPC
    is impossible not fully commit at launch time. The guest would EREMOVE all
    pages during initialization resulting #PF and all pages allocated. This
    essentially makes "prealloc=off" the same as "prealloc=on".
    Unless you are talking about some custom OS or kernel other than upstream
    Linux here?

    Thanks
    Haitap

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