RE: [PATCH v2] x86/hyperv: Fix kexec panic/hang issues

[Michael Kelley]

From: Dexuan Cui <decui@xxxxxxxxxxxxx> Sent: Monday, December 21, 2020 10:56 PM
> 
> 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@xxxxxxxxxxxxx>
> ---
> 
> Changes in v2:
> 	Improved the commit log as Michael Kelley suggested.
> 	No change to v1 otherwise.
> 
>  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(-)
> 

Reviewed-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>