[GIT,PULL,28/28] s390/mm: optimize locking without huge pages in gmap_pmd_op_walk()
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Message ID 20181002070655.224110-29-borntraeger@de.ibm.com
State New
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Series
  • [GIT,PULL,01/28] KVM: s390: vsie: simulate VCPU SIE entry/exit
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Commit Message

Christian Borntraeger Oct. 2, 2018, 7:06 a.m. UTC
From: David Hildenbrand <david@redhat.com>

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>
---
 arch/s390/mm/gmap.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

Patch
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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;
 	}