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 /include | |
| parent | 342d3db763f2621ed4546ebf8f6c61cb29d7fbdb (diff) | |
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 'include')
| -rw-r--r-- | include/linux/kvm_host.h | 14 |
1 files changed, 9 insertions, 5 deletions
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h index d4d4d7092110..eada8e69fe58 100644 --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -702,12 +702,16 @@ static inline int mmu_notifier_retry(struct kvm_vcpu *vcpu, unsigned long mmu_se if (unlikely(vcpu->kvm->mmu_notifier_count)) return 1; /* - * Both reads happen under the mmu_lock and both values are - * modified under mmu_lock, so there's no need of smb_rmb() - * here in between, otherwise mmu_notifier_count should be - * read before mmu_notifier_seq, see - * mmu_notifier_invalidate_range_end write side. + * Ensure the read of mmu_notifier_count happens before the read + * of mmu_notifier_seq. This interacts with the smp_wmb() in + * mmu_notifier_invalidate_range_end to make sure that the caller + * either sees the old (non-zero) value of mmu_notifier_count or + * the new (incremented) value of mmu_notifier_seq. + * PowerPC Book3s HV KVM calls this under a per-page lock + * rather than under kvm->mmu_lock, for scalability, so + * can't rely on kvm->mmu_lock to keep things ordered. */ + smp_rmb(); if (vcpu->kvm->mmu_notifier_seq != mmu_seq) return 1; return 0; |