linux-kernel - Re: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo regs

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Message-ID: <53DA7583.2030504@redhat.com>
Date:	Thu, 31 Jul 2014 18:57:39 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Alex Bennée <alex.bennee@...aro.org>,
	kvmarm@...ts.cs.columbia.edu, linux-arm-kernel@...ts.infradead.org
CC:	kvm@...r.kernel.org,
	Christoffer Dall <christoffer.dall@...aro.org>,
	Marc Zyngier <marc.zyngier@....com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Gleb Natapov <gleb@...nel.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] arm64: KVM: export current vcpu->pause state via pseudo
 regs

Il 09/07/2014 15:55, Alex Bennée ha scritto:
> 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 Bennée <alex.bennee@...aro.org>
> ---
>  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?

How is this represented within QEMU in TCG mode?  Also, how is KVM/ARM
representing (and passing to QEMU) the halted state of the VCPU?

Paolo
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