Marcelo Tosatti wrote:
===================================================================
--- kvm-irqlock.orig/virt/kvm/coalesced_mmio.c
+++ kvm-irqlock/virt/kvm/coalesced_mmio.c
@@ -26,9 +26,12 @@ static int coalesced_mmio_in_range(struc
if (!is_write)
return 0;
- /* kvm->lock is taken by the caller and must be not released before
- * dev.read/write
- */
+ /*
+ * Some other vcpu might be batching data into the ring,
+ * fallback to userspace. Ordering not our problem.
+ */
+ if (!atomic_add_unless(&dev->in_use, 1, 1))
+ return 0;
Ordering with simultaneous writes is indeed not our problem, but the
ring may contain ordered writes (even by the same vcpu!)
You mean writes by a vcpu should maintain ordering even when that vcpu
migrates to a different pcpu?
No. Writes by a single vcpu need to preserve their ordering relative to
each other. If a write by vcpu A completes before a write by vcpu B
starts, then they need to be ordered, since the vcpus may have
synchronized in between.
Hm, I don't thimk you broke these rules.
The smp_wmb in coalesced_write guarantees that.
Suggest our own lock here. in_use is basically a homemade lock, better
to use the factory made ones which come with a warranty.
The first submission had a mutex but was considered unorthodox. Although
i agree with your argument made then, i don't see a way around that.
Some pseudocode please?
Why not use slots_lock to protect the entire iodevice list (rcu one
day), and an internal spinlock for coalesced mmio?
--
error compiling committee.c: too many arguments to function
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