From ab99a1cc7a405fed5148cf6a6fc26eec75b8a7a7 Mon Sep 17 00:00:00 2001 From: Christian Borntraeger Date: Wed, 3 Feb 2016 10:18:41 +0100 Subject: [PATCH] KVM: s390: do not take mmap_sem on dirty log query Dirty log query can take a long time for huge guests. Holding the mmap_sem for very long times can cause some unwanted latencies. Turns out that we do not need to hold the mmap semaphore. We hold the slots_lock for gfn->hva translation and walk the page tables with that address, so no need to look at the VMAs. KVM also holds a reference to the mm, which should prevent other things going away. During the walk we take the necessary ptl locks. Signed-off-by: Christian Borntraeger Reviewed-by: David Hildenbrand Signed-off-by: Christian Borntraeger --- arch/s390/kvm/kvm-s390.c | 2 -- 1 file changed, 2 deletions(-) diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c index d0dcf73f36bc..d4bcd863b24a 100644 --- a/arch/s390/kvm/kvm-s390.c +++ b/arch/s390/kvm/kvm-s390.c @@ -274,7 +274,6 @@ static void kvm_s390_sync_dirty_log(struct kvm *kvm, unsigned long address; struct gmap *gmap = kvm->arch.gmap; - down_read(&gmap->mm->mmap_sem); /* Loop over all guest pages */ last_gfn = memslot->base_gfn + memslot->npages; for (cur_gfn = memslot->base_gfn; cur_gfn <= last_gfn; cur_gfn++) { @@ -283,7 +282,6 @@ static void kvm_s390_sync_dirty_log(struct kvm *kvm, if (gmap_test_and_clear_dirty(address, gmap)) mark_page_dirty(kvm, cur_gfn); } - up_read(&gmap->mm->mmap_sem); } /* Section: vm related */ -- 2.20.1