On 07/18/2011 01:15 PM, Sasha Levin wrote:
On Mon, 2011-07-18 at 12:50 +0300, Avi Kivity wrote: > On 07/18/2011 12:29 PM, Sasha Levin wrote: > > > 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 > > It's "locked" using rcu. > Where is that happening? All the coalesced zones are stored under the coalesced "device" in a simple array. When adding and removing zones, kvm->slots_lock is taken - I don't see anything which prevents a range check during zone removal unless slots_lock prevents IO.
Range check during slot removal is legal. While you are removing a slot, a concurrent write may hit or miss the slot; it doesn't matter.
Userspace should flush the coalesced mmio buffer after removal to ensure there are no pending writes.
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