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    SubjectRe: [PATCH v2] x86/hyperv: Fix kexec panic/hang issues
    On Mon, Dec 21, 2020 at 10:55:41PM -0800, Dexuan Cui wrote:
    > Currently the kexec kernel can panic or hang due to 2 causes:
    >
    > 1) hv_cpu_die() is not called upon kexec, so the hypervisor corrupts the
    > old VP Assist Pages when the kexec kernel runs. The same issue is fixed
    > for hibernation in commit 421f090c819d ("x86/hyperv: Suspend/resume the
    > VP assist page for hibernation"). Now fix it for kexec.
    >
    > 2) hyperv_cleanup() is called too early. In the kexec path, the other CPUs
    > are stopped in hv_machine_shutdown() -> native_machine_shutdown(), so
    > between hv_kexec_handler() and native_machine_shutdown(), the other CPUs
    > can still try to access the hypercall page and cause panic. The workaround
    > "hv_hypercall_pg = NULL;" in hyperv_cleanup() is unreliabe. Move
    > hyperv_cleanup() to a better place.
    >
    > Signed-off-by: Dexuan Cui <decui@microsoft.com>

    The code looks a bit intrusive. On the other hand, this does sound like
    something needs backporting for older stable kernels.

    On a more practical note, I need to decide whether to take it via
    hyperv-fixes or hyperv-next. What do you think?

    Wei.

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