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s390/mm: optimize locking without huge pages in gmap_pmd_op_walk()
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). Let's make this a special case, so gmap_protect_range() and gmap_sync_dirty_log_pmd() will not take the lock when huge pages are not allowed. gmap_protect_range() is called quite frequently for managing shadow page tables in vSIE environments. Signed-off-by: David Hildenbrand <david@redhat.com> Reviewed-by: Janosch Frank <frankja@linux.ibm.com> Message-Id: <20180806155407.15252-1-david@redhat.com> Signed-off-by: Janosch Frank <frankja@linux.ibm.com>
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1 changed files with 8 additions and 2 deletions
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@ -905,10 +905,16 @@ static inline pmd_t *gmap_pmd_op_walk(struct gmap *gmap, unsigned long gaddr)
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pmd_t *pmdp;
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BUG_ON(gmap_is_shadow(gmap));
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spin_lock(&gmap->guest_table_lock);
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pmdp = (pmd_t *) gmap_table_walk(gmap, gaddr, 1);
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if (!pmdp)
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return NULL;
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if (!pmdp || pmd_none(*pmdp)) {
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/* without huge pages, there is no need to take the table lock */
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if (!gmap->mm->context.allow_gmap_hpage_1m)
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return pmd_none(*pmdp) ? NULL : pmdp;
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spin_lock(&gmap->guest_table_lock);
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if (pmd_none(*pmdp)) {
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spin_unlock(&gmap->guest_table_lock);
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return NULL;
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}
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