Gleb Natapov wrote:
On Thu, Apr 08, 2010 at 02:27:53PM +0900, Yoshiaki Tamura wrote:
Avi Kivity wrote:
On 04/07/2010 08:21 PM, Yoshiaki Tamura wrote:
The problem here is that, I needed to transfer the VM state which is
just *before* the output to the devices. Otherwise, the VM state has
already been proceeded, and after failover, some I/O didn't work as I
expected.
I tracked down this issue, and figured out rip was already proceeded
in KVM,
and transferring this VCPU state was meaningless.
I'm planning to post the patch set of Kemari soon, but I would like to
solve
this rip issue before that. If there is no drawback, I'm happy to work
and post a patch.
vcpu state is undefined when an mmio operation is pending,
Documentation/kvm/api.txt says the following:
NOTE: For KVM_EXIT_IO, KVM_EXIT_MMIO and KVM_EXIT_OSI, the corresponding
operations are complete (and guest state is consistent) only after
userspace
has re-entered the kernel with KVM_RUN. The kernel side will first finish
incomplete operations and then check for pending signals. Userspace
can re-enter the guest with an unmasked signal pending to complete
pending operations.
Thanks for the information.
So the point is the vcpu state that can been observed from qemu upon
KVM_EXIT_IO, KVM_EXIT_MMIO and KVM_EXIT_OSI should not be used
because it's not complete/consistent?
Definitely. VCPU is in the middle of an instruction execution, so the
state is undefined. One instruction may generate more then one IO exit
during its execution BTW.
Regarding the multiple IO exits, we're paying attention too. Although it
depends on the guest behavior, if we limit the device model, one IO exit per one
instruction may be practical at beggining. But thanks for pointing out.
To solve the undefined VCPU state, how about keeping a copy of initial state
upon VMEXIT? I guess there already is a similar shadow state in KVM. If
possible we can allocate another one for this purpose.
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