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From:   Michael Kelley <mikelley@microsoft.com>
To:     Dexuan Cui <decui@microsoft.com>,
        "tglx@linutronix.de" <tglx@linutronix.de>,
        "mingo@redhat.com" <mingo@redhat.com>,
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        "wei.liu@kernel.org" <wei.liu@kernel.org>,
        vkuznets <vkuznets@redhat.com>,
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CC:     "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>
Subject: RE: [PATCH v2] x86/hyperv: Fix kexec panic/hang issues
Thread-Topic: [PATCH v2] x86/hyperv: Fix kexec panic/hang issues
Thread-Index: AQHW2C+JeK2pk6EyK0KhohVBANde/KoDIOnw
Date:   Tue, 22 Dec 2020 13:45:52 +0000
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References: <20201222065541.24312-1-decui@microsoft.com>
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From: Dexuan Cui <decui@microsoft.com> Sent: Monday, December 21, 2020 10:5=
6 PM
>=20
> Currently the kexec kernel can panic or hang due to 2 causes:
>=20
> 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.
>=20
> 2) hyperv_cleanup() is called too early. In the kexec path, the other CPU=
s
> 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 workaroun=
d
> "hv_hypercall_pg =3D NULL;" in hyperv_cleanup() is unreliabe. Move
> hyperv_cleanup() to a better place.
>=20
> Signed-off-by: Dexuan Cui <decui@microsoft.com>
> ---
>=20
> Changes in v2:
> 	Improved the commit log as Michael Kelley suggested.
> 	No change to v1 otherwise.
>=20
>  arch/x86/hyperv/hv_init.c       |  4 ++++
>  arch/x86/include/asm/mshyperv.h |  2 ++
>  arch/x86/kernel/cpu/mshyperv.c  | 18 ++++++++++++++++++
>  drivers/hv/vmbus_drv.c          |  2 --
>  4 files changed, 24 insertions(+), 2 deletions(-)
>=20

Reviewed-by: Michael Kelley <mikelley@microsoft.com>