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

Stanislav Kinsburskii
2026-04-28T23:31:40Z

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>

Reviewed-by: Stanislav Kinsburskii <skinsburskii@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__);
> - return PTR_ERR(mshv_debugfs);
> + return err;
> }
>
> if (hv_root_partition()) {
> @@ -710,6 +712,9 @@ int __init mshv_debugfs_init(void)
>
> void mshv_debugfs_exit(void)
> {
> + if (!mshv_debugfs)
> + return;
> +
> mshv_debugfs_parent_partition_remove();
>
> if (hv_root_partition()) {
> diff --git a/drivers/hv/mshv_synic.c b/drivers/hv/mshv_synic.c
> index 978a1cace341..88170ce6b83f 100644
> --- a/drivers/hv/mshv_synic.c
> +++ b/drivers/hv/mshv_synic.c
> @@ -723,6 +723,7 @@ mshv_unregister_doorbell(u64 partition_id, int doorbell_portid)
> static int mshv_synic_reboot_notify(struct notifier_block *nb,
> unsigned long code, void *unused)
> {
> + mshv_debugfs_exit();
> cpuhp_remove_state(synic_cpuhp_online);
> return 0;
> }
> --
> 2.43.0
>