On Mon, 2011-07-18 at 11:11 +0300, Avi Kivity wrote: > On 07/15/2011 02:37 PM, Sasha Levin wrote: > > Move the check whether there are available entries to within the spinlock. > > This allows working with larger amount of VCPUs and reduces premature > > exits when using a large number of VCPUs. > > > > Cc: Avi Kivity<[email protected]> > > Cc: Ingo Molnar<[email protected]> > > Cc: Marcelo Tosatti<[email protected]> > > Cc: Pekka Enberg<[email protected]> > > Signed-off-by: Sasha Levin<[email protected]> > > --- > > virt/kvm/coalesced_mmio.c | 9 ++++++--- > > 1 files changed, 6 insertions(+), 3 deletions(-) > > > > diff --git a/virt/kvm/coalesced_mmio.c b/virt/kvm/coalesced_mmio.c > > index fc84875..34188db 100644 > > --- a/virt/kvm/coalesced_mmio.c > > +++ b/virt/kvm/coalesced_mmio.c > > @@ -37,7 +37,7 @@ static int coalesced_mmio_in_range(struct > > kvm_coalesced_mmio_dev *dev, > > */ > > ring = dev->kvm->coalesced_mmio_ring; > > avail = (ring->first - ring->last - 1) % KVM_COALESCED_MMIO_MAX; > > - if (avail< KVM_MAX_VCPUS) { > > + if (avail == 0) { > > /* full */ > > return 0; > > } > > @@ -63,11 +63,14 @@ static int coalesced_mmio_write(struct kvm_io_device > > *this, > > { > > struct kvm_coalesced_mmio_dev *dev = to_mmio(this); > > struct kvm_coalesced_mmio_ring *ring = dev->kvm->coalesced_mmio_ring; > > - if (!coalesced_mmio_in_range(dev, addr, len)) > > - return -EOPNOTSUPP; > > > > spin_lock(&dev->lock); > > > > + if (!coalesced_mmio_in_range(dev, addr, len)) { > > + spin_unlock(&dev->lock); > > + return -EOPNOTSUPP; > > + } > > + > > /* copy data in first free entry of the ring */ > > Hmm. This means we take the lock for every I/O, whether it hits > coalesced mmio or not. > > We need to do the range check before taking the lock and the space check > after taking the lock. >
I'll fix that. Shouldn't the range check be also locked somehow? Currently it is possible that a coalesced region was removed while we are checking the ranges, and we won't issue a mmio exit as the host expects. -- Sasha. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html
