On 06.08.2018 17:54, David Hildenbrand wrote: > Right now we temporarily take the page table lock in gmap_pmd_op_walk() > even though we know we won't need it (if we can never have 1mb pages > mapped into the gmap). > > So let's special case this, so > gmap_protect_range()/gmap_sync_dirty_log_pmd() will not take the lock in > case huge pages are not allowed.
So, let's make this a special case > > gmap_protect_range() is called quite frequently for managing shadow > page tables in vSIE environments. > > Signed-off-by: David Hildenbrand <[email protected]> If you make the patch title more specific: Reviewed-by: Janosch Frank <[email protected]> I considered getting rid of the last unlock with the !large check, but in theory somebody could run a VM with the HPAGE CAP and 4k pages which would then result in havoc if we wouldn't also adapt gmap_pmd_op_end. > --- > arch/s390/mm/gmap.c | 10 ++++++++-- > 1 file changed, 8 insertions(+), 2 deletions(-) > > diff --git a/arch/s390/mm/gmap.c b/arch/s390/mm/gmap.c > index bb44990c8212..d4fa0a4514e0 100644 > --- a/arch/s390/mm/gmap.c > +++ b/arch/s390/mm/gmap.c > @@ -905,10 +905,16 @@ static inline pmd_t *gmap_pmd_op_walk(struct gmap > *gmap, unsigned long gaddr) > pmd_t *pmdp; > > BUG_ON(gmap_is_shadow(gmap)); > - spin_lock(&gmap->guest_table_lock); > pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1); > + if (!pmdp) > + return NULL; > > - if (!pmdp || pmd_none(*pmdp)) { > + /* without huge pages, there is no need to take the table lock */ > + if (!gmap->mm->context.allow_gmap_hpage_1m) > + return pmd_none(*pmdp) ? NULL : pmdp; > + > + spin_lock(&gmap->guest_table_lock); > + if (pmd_none(*pmdp)) { > spin_unlock(&gmap->guest_table_lock); > return NULL; > } >
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