Re: [PATCH] KVM: Fix QEmu interrupted HLT emulation

[Avi Kivity <avi@qumranet.com>]

Yang, Sheng wrote:
> From: Sheng Yang <sheng.yang@intel.com>
> Date: Thu, 31 Jul 2008 13:43:58 +0800
> Subject: [PATCH] KVM: Fix QEmu interrupted HLT emulation
>
> QEmu can interrupt VCPU from HLT emulation without setting mp_state to
> MP_STATE_RUNNABLE, when it kick vcpus which are doing HLT emulation to 
> do something like "stop" or "info cpus". Here are two issues of this 
> behaviour:
>
> First, if vcpu exit to QEmu with MP_STATE_HALTED, it would keep in 
> this state later for vcpu_run(), which is eerie...
>
> Second, a practical problem: bios load AP boot up code to 0x10000 
> (now), and AP is running HLT there. But later grub load it's stage2 
> code to the same address. Then if the halting vcpu was forced exit to 
> QEmu in grub, and come back for vcpu_run later, it can't execute HLT 
> instruction anymore, just because the bios code is not there,
> and it would follow a piece of code of grub, which would cause 
> completely chaos...
>
> The second issue directly lead to guest crash or SMP linux can't boot 
> up AP later if we "stop" or "info cpus" in grub. Though I also sent a 
> patch for BIOS, it's necessary to get correct behavior here.
>   

Going over my backlog it looks like I missed this.  But I think
Marcelo's rework obsoletes this patch?


-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.