Re: [PATCH v1 1/1] KVM: s390: Fix missing present bit for gmap puds

Balbir Singh
2025-10-28T21:23:31Z

On 10/29/25 00:01, Claudio Imbrenda wrote:
> For hugetlbs, gmap puds have the present bit set. For normal puds
> (which point to ptes), the bit is not set. This is in contrast to the
> normal userspace puds, which always have the bit set for present pmds.
>
> This causes issues when ___pte_offset_map() is modified to only check
> for the present bit.
>
> The solution to the problem is simply to always set the present bit for
> present gmap pmds.
>
> Signed-off-by: Claudio Imbrenda <imbrenda@linux.ibm.com>
> Link: https://lore.kernel.org/lkml/20251017144924.10034-1-borntraeger@linux.ibm.com/
> Tested-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> Acked-by: Christian Borntraeger <borntraeger@linux.ibm.com>
> ---
> arch/s390/mm/gmap.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c
> index 8ff6bba107e8..22c448b32340 100644
> --- a/arch/s390/mm/gmap.c
> +++ b/arch/s390/mm/gmap.c
> @@ -599,8 +599,9 @@ int __gmap_link(struct gmap *gmap, unsigned long gaddr, unsigned long vmaddr)
> | _SEGMENT_ENTRY_GMAP_UC
> | _SEGMENT_ENTRY;
> } else
> - *table = pmd_val(*pmd) &
> - _SEGMENT_ENTRY_HARDWARE_BITS;
> + *table = (pmd_val(*pmd) &
> + _SEGMENT_ENTRY_HARDWARE_BITS)
> + | _SEGMENT_ENTRY;
> }
> } else if (*table & _SEGMENT_ENTRY_PROTECT &&
> !(pmd_val(*pmd) & _SEGMENT_ENTRY_PROTECT)) {

Acked-by: Balbir Singh <balbirs@nvidia.com>