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    SubjectRe: [PATCH v4 00/75] x86: SEV-ES Guest Support
    On Wed, Jul 15, 2020 at 11:24:56AM +0200, Peter Zijlstra wrote:
    > Can we get some more words -- preferably in actual code comments, on
    > when exactly #VC happens?

    Sure, will add this as a comment before the actual runtime VC handler.

    > Because the only thing I remember is that #VC could happen on any memop,
    > but I also have vague memories of that being a later extention.

    Currently it is only raised when something happens that the hypervisor
    intercepts, for example on a couple of instructions like CPUID,
    RD/WRMSR, ..., or on MMIO/IOIO accesses.

    With Secure Nested Paging (SNP), which needs additional enablement, a #VC can
    happen on any memory access. I wrote the IST handling entry code for #VC
    with that in mind, but do not actually enable it. This is the reason why
    the #VC handler just panics the system when it ends up on the fall-back
    (VC2) stack, with SNP enabled it needs to handle the SNP exit-codes in
    that path.

    Regards,

    Joerg

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