Il 31/07/2014 19:04, Peter Maydell ha scritto:

On 31 July 2014 17:57, Paolo Bonzini [off-list ref] wrote:

quoted

Il 09/07/2014 15:55, Alex Benn?e ha scritto:

quoted

To cleanly restore an SMP VM we need to ensure that the current pause
state of each vcpu is correctly recorded. Things could get confused if
the CPU starts running after migration restore completes when it was
paused before it state was captured.

I've done this by exposing a register (currently only 1 bit used) via
the GET/SET_ONE_REG logic to pass the state between KVM and the VM
controller (e.g. QEMU).

Signed-off-by: Alex Benn?e <redacted>
---
 arch/arm64/include/uapi/asm/kvm.h |  8 +++++
 arch/arm64/kvm/guest.c            | 61 ++++++++++++++++++++++++++++++++++++++-
 2 files changed, 68 insertions(+), 1 deletion(-)

Since it's a pseudo register anyway, would it make sense to use the
existing KVM_GET/SET_MP_STATE ioctl interface?

That appears to be an x86-specific thing relating to
IRQ chips.

No, it's not.  It's just the state of the CPU, s390 will be using it too.

On x86 the states are uninitialized (UNINITIALIZED), stopped
(INIT_RECEIVED), running (RUNNABLE), halted (HALTED).  CPU 0 starts in
RUNNABLE state, other CPUs start in UNINITIALIZED state.  There are
x86-specific cases (uninitialized) and x86-isms (the INIT_RECEIVED
name), but the idea is widely applicable.

quoted

Also, how is KVM/ARM
representing (and passing to QEMU) the halted state of the
VCPU?

We don't. In ARM the equivalent of x86 HLT (which is
WFI, wait-for-interrupt) is allowed to resume at any time.
So we don't need to care about saving and restoring
whether we were sat in a WFI at point of migration.

What does ARM do if you have a WFI while interrupts are disabled?  On
x86 after "cli;hlt" only an NMI will wake you up.  With spurious
wakeups, it's pretty much guaranteed that you will break such "cli;hlt"
sequences.

Paolo