Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx> writes:
> On machines without the Destroy Secure Configuration Fast UVC, the
> topmost level of page tables is set aside and freed asynchronously
> as last step of the asynchronous teardown.
>
> Each gmap has a host_to_guest radix tree mapping host (userspace)
> addresses (with 1M granularity) to gmap segment table entries (pmds).
>
> If a guest is smaller than 2GB, the topmost level of page tables is the
> segment table (i.e. there are only 2 levels). Replacing it means that
> the pointers in the host_to_guest mapping would become stale and cause
> all kinds of nasty issues.
>
> This patch fixes the issue by synchronously destroying all guests with
> only 2 levels of page tables in kvm_s390_pv_set_aside. This will
> speed up the process and avoid the issue altogether.
>
> Update s390_replace_asce so it refuses to replace segment type ASCEs.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@xxxxxxxxxxxxx>
> Fixes: fb491d5500a7 ("KVM: s390: pv: asynchronous destroy for reboot")
> ---
> arch/s390/kvm/pv.c | 35 ++++++++++++++++++++---------------
> arch/s390/mm/gmap.c | 7 +++++++
> 2 files changed, 27 insertions(+), 15 deletions(-)
>
> diff --git a/arch/s390/kvm/pv.c b/arch/s390/kvm/pv.c
> index e032ebbf51b9..ceb8cb628d62 100644
> --- a/arch/s390/kvm/pv.c
> +++ b/arch/s390/kvm/pv.c
> @@ -39,6 +39,7 @@ struct pv_vm_to_be_destroyed {
> u64 handle;
> void *stor_var;
> unsigned long stor_base;
> + bool small;
I would rather use a more verbose variable name (maybe ‘lower_2g‘
accordingly to the `kvm_s390_destroy_lower_2g` function name or even
better something indicating the actual implications).
At least, I would add a comment what ‘small‘ means and the implications
of it.
[…snip]
