diff options
| author | Paul Mackerras <paulus@samba.org> | 2011-12-12 12:37:21 +0000 |
|---|---|---|
| committer | Avi Kivity <avi@redhat.com> | 2012-03-05 14:52:38 +0200 |
| commit | a355aa54f1d25dff83c0feef8863d83a76988fdb (patch) | |
| tree | 4fe27e8dd1a3935757b319726a8b8bdc10496930 /virt | |
| parent | 342d3db763f2621ed4546ebf8f6c61cb29d7fbdb (diff) | |
| download | lwn-a355aa54f1d25dff83c0feef8863d83a76988fdb.tar.gz lwn-a355aa54f1d25dff83c0feef8863d83a76988fdb.zip | |
KVM: Add barriers to allow mmu_notifier_retry to be used locklessly
This adds an smp_wmb in kvm_mmu_notifier_invalidate_range_end() and an
smp_rmb in mmu_notifier_retry() so that mmu_notifier_retry() will give
the correct answer when called without kvm->mmu_lock being held.
PowerPC Book3S HV KVM wants to use a bitlock per guest page rather than
a single global spinlock in order to improve the scalability of updates
to the guest MMU hashed page table, and so needs this.
Signed-off-by: Paul Mackerras <paulus@samba.org>
Acked-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Avi Kivity <avi@redhat.com>
Diffstat (limited to 'virt')
| -rw-r--r-- | virt/kvm/kvm_main.c | 6 |
1 files changed, 3 insertions, 3 deletions
diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c index 64be836f3348..9f32bffd37c0 100644 --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -357,11 +357,11 @@ static void kvm_mmu_notifier_invalidate_range_end(struct mmu_notifier *mn, * been freed. */ kvm->mmu_notifier_seq++; + smp_wmb(); /* * The above sequence increase must be visible before the - * below count decrease but both values are read by the kvm - * page fault under mmu_lock spinlock so we don't need to add - * a smb_wmb() here in between the two. + * below count decrease, which is ensured by the smp_wmb above + * in conjunction with the smp_rmb in mmu_notifier_retry(). */ kvm->mmu_notifier_count--; spin_unlock(&kvm->mmu_lock); |