Re: [PATCH v4 3/3] mshv: unmap debugfs stats pages on kexec

[Anirudh Rayabharam <anirudh@anirudhrb.com>]

On Mon, Apr 27, 2026 at 02:38:54PM -0700, Jork Loeser wrote:
> On L1VH, debugfs stats pages are overlay pages: the kernel allocates
> them and registers the GPAs with the hypervisor via
> HVCALL_MAP_STATS_PAGE2. These overlay mappings persist in the
> hypervisor across kexec. If the kexec'd kernel reuses those physical
> pages, the hypervisor's overlay semantics cause a machine check
> exception.
> 
> Fix this by calling mshv_debugfs_exit() from the reboot notifier,
> which issues HVCALL_UNMAP_STATS_PAGE for each mapped stats page before
> kexec. This releases the overlay bindings so the physical pages can be
> safely reused. Guard mshv_debugfs_exit() against being called when
> init failed.
> 
> Signed-off-by: Jork Loeser <jloeser@linux.microsoft.com>
> ---
>  drivers/hv/mshv_debugfs.c | 7 ++++++-
>  drivers/hv/mshv_synic.c   | 1 +
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hv/mshv_debugfs.c b/drivers/hv/mshv_debugfs.c
> index 418b6dc8f3c2..3c3e02237ae9 100644
> --- a/drivers/hv/mshv_debugfs.c
> +++ b/drivers/hv/mshv_debugfs.c
> @@ -674,8 +674,10 @@ int __init mshv_debugfs_init(void)
>  
>  	mshv_debugfs = debugfs_create_dir("mshv", NULL);
>  	if (IS_ERR(mshv_debugfs)) {
> +		err = PTR_ERR(mshv_debugfs);
> +		mshv_debugfs = NULL;
>  		pr_err("%s: failed to create debugfs directory\n", __func__);

Might as well print err here.

Nevertheless:

Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>

Thanks,
Anirudh.