linux-kernel - Re: [PATCH v2] x86/hyperv: Fix kexec panic/hang issues

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Message-ID: <20210105130423.nvxpsdvgn5zier4v@liuwe-devbox-debian-v2>
Date:   Tue, 5 Jan 2021 13:04:23 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     Dexuan Cui <decui@...rosoft.com>
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de, x86@...nel.org,
        hpa@...or.com, linux-hyperv@...r.kernel.org,
        mikelley@...rosoft.com, wei.liu@...nel.org, vkuznets@...hat.com,
        jwiesner@...e.com, ohering@...e.com, linux-kernel@...r.kernel.org,
        sthemmin@...rosoft.com, haiyangz@...rosoft.com, kys@...rosoft.com
Subject: Re: [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@...rosoft.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.