Re: [PATCH v9 11/18] s390/mm: KVM: pv: when tearing down, try to destroy protected pages

Janosch Frank
2022-03-31T13:34:51Z

On 3/30/22 14:25, Claudio Imbrenda wrote:
> When ptep_get_and_clear_full is called for a mm teardown, we will now
> attempt to destroy the secure pages. This will be faster than export.
>
> In case it was not a teardown, or if for some reason the destroy page
> UVC failed, we try with an export page, like before.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Acked-by: Janosch Frank <frankja@linux.ibm.com>
> ---
> arch/s390/include/asm/pgtable.h | 18 +++++++++++++++---
> 1 file changed, 15 insertions(+), 3 deletions(-)
>
> diff --git a/arch/s390/include/asm/pgtable.h b/arch/s390/include/asm/pgtable.h
> index 23ca0d8e058a..72544a1b4a68 100644
> --- a/arch/s390/include/asm/pgtable.h
> +++ b/arch/s390/include/asm/pgtable.h
> @@ -1118,9 +1118,21 @@ static inline pte_t ptep_get_and_clear_full(struct mm_struct *mm,
> } else {
> res = ptep_xchg_lazy(mm, addr, ptep, __pte(_PAGE_INVALID));
> }
> - /* At this point the reference through the mapping is still present */
> - if (mm_is_protected(mm) && pte_present(res))
> - uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
> + /* Nothing to do */
> + if (!mm_is_protected(mm) || !pte_present(res))
> + return res;
> + /*
> + * At this point the reference through the mapping is still present.

That's the case because we zap ptes within a mm that's still existing,
right? The mm will be deleted after we have unmapped the memory.

> + * The notifier should have destroyed all protected vCPUs at this
> + * point, so the destroy should be successful.
> + */
> + if (full && !uv_destroy_owned_page(pte_val(res) & PAGE_MASK))
> + return res;
> + /*
> + * But if something went wrong and the pages could not be destroyed,
> + * the slower export is used as fallback instead.
> + */
> + uv_convert_owned_from_secure(pte_val(res) & PAGE_MASK);
> return res;
> }
>