Re: [PATCH v2] x86/hyperv: fix kexec crash due to VP assist page corruption

[Wei Liu <wei.liu@kernel.org>]

On Wed, Aug 28, 2024 at 04:51:56PM +0530, Anirudh Rayabharam wrote:
> From: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
> 
> commit 9636be85cc5b ("x86/hyperv: Fix hyperv_pcpu_input_arg handling when
> CPUs go online/offline") introduces a new cpuhp state for hyperv
> initialization.
> 
> cpuhp_setup_state() returns the state number if state is
> CPUHP_AP_ONLINE_DYN or CPUHP_BP_PREPARE_DYN and 0 for all other states.
> For the hyperv case, since a new cpuhp state was introduced it would
> return 0. However, in hv_machine_shutdown(), the cpuhp_remove_state() call
> is conditioned upon "hyperv_init_cpuhp > 0". This will never be true and
> so hv_cpu_die() won't be called on all CPUs. This means the VP assist page
> won't be reset. When the kexec kernel tries to setup the VP assist page
> again, the hypervisor corrupts the memory region of the old VP assist page
> causing a panic in case the kexec kernel is using that memory elsewhere.
> This was originally fixed in commit dfe94d4086e4 ("x86/hyperv: Fix kexec
> panic/hang issues").
> 
> Get rid of hyperv_init_cpuhp entirely since we are no longer using a
> dynamic cpuhp state and use CPUHP_AP_HYPERV_ONLINE directly with
> cpuhp_remove_state().
> 
> Cc: stable@vger.kernel.org
> Fixes: 9636be85cc5b ("x86/hyperv: Fix hyperv_pcpu_input_arg handling when CPUs go online/offline")
> Signed-off-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>

Applied to hyperv-fixes, thanks!