Re: [PATCH resend RFC 8/9] s390/mm: optimize set_guest_storage_key()

Claudio Imbrenda
2021-09-27T17:09:11Z

On Thu, 9 Sep 2021 18:22:47 +0200
David Hildenbrand <david@redhat.com> wrote:

> We already optimize get_guest_storage_key() to assume that if we don't have
> a PTE table and don't have a huge page mapped that the storage key is 0.
>
> Similarly, optimize set_guest_storage_key() to simply do nothing in case
> the key to set is 0.
>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Claudio Imbrenda <imbrenda@linux.ibm.com>

> ---
> arch/s390/mm/pgtable.c | 14 ++++++++++++--
> 1 file changed, 12 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/pgtable.c b/arch/s390/mm/pgtable.c
> index 4e77b8ebdcc5..534939a3eca5 100644
> --- a/arch/s390/mm/pgtable.c
> +++ b/arch/s390/mm/pgtable.c
> @@ -792,13 +792,23 @@ int set_guest_storage_key(struct mm_struct *mm, unsigned long addr,
> pmd_t *pmdp;
> pte_t *ptep;
>
> - if (pmd_lookup(mm, addr, &pmdp))
> + /*
> + * If we don't have a PTE table and if there is no huge page mapped,
> + * we can ignore attempts to set the key to 0, because it already is 0.
> + */
> + switch (pmd_lookup(mm, addr, &pmdp)) {
> + case -ENOENT:
> + return key ? -EFAULT : 0;
> + case 0:
> + break;
> + default:
> return -EFAULT;
> + }
>
> ptl = pmd_lock(mm, pmdp);
> if (!pmd_present(*pmdp)) {
> spin_unlock(ptl);
> - return -EFAULT;
> + return key ? -EFAULT : 0;
> }
>
> if (pmd_large(*pmdp)) {