Re: [PATCH 2/2] kvm/x86: Hyper-V kvm exit

2015-10-12 Thread Roman Kagan
On Fri, Oct 09, 2015 at 04:41:15PM +0200, Paolo Bonzini wrote:
> On 09/10/2015 15:39, Denis V. Lunev wrote:
> > A new vcpu exit is introduced to notify the userspace of the
> > changes in Hyper-V synic configuraion triggered by guest writing to the
> > corresponding MSRs.
> 
> Why is this exit necessary?

The guest writes to synic-related MSRs and that should take "immediate"
effect.

E.g. it may decide to disable or relocate the message page by writing to
SIMP MSR.  The host is then supposed to stop accessing the old message
page before the vCPU proceeds to the next instruction.  Hence the exit,
to allow the userspace to react accordingly before reentering the guest.

Roman.
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Re: [PATCH 2/2] kvm/x86: Hyper-V kvm exit

2015-10-09 Thread Paolo Bonzini


On 09/10/2015 15:39, Denis V. Lunev wrote:
> From: Andrey Smetanin 
> 
> A new vcpu exit is introduced to notify the userspace of the
> changes in Hyper-V synic configuraion triggered by guest writing to the
> corresponding MSRs.
> 
> Signed-off-by: Andrey Smetanin 
> Reviewed-by: Roman Kagan 
> Signed-off-by: Denis V. Lunev 
> CC: Vitaly Kuznetsov 
> CC: "K. Y. Srinivasan" 
> CC: Gleb Natapov 
> CC: Paolo Bonzini 

Why is this exit necessary?

Paolo
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Re: [PATCH 2/2] kvm/x86: Hyper-V kvm exit

2015-10-09 Thread Paolo Bonzini


On 09/10/2015 16:53, Roman Kagan wrote:
>> > Why is this exit necessary?
> The guest writes to synic-related MSRs and that should take "immediate"
> effect.
> 
> E.g. it may decide to disable or relocate the message page by writing to
> SIMP MSR.  The host is then supposed to stop accessing the old message
> page before the vCPU proceeds to the next instruction.  Hence the exit,
> to allow the userspace to react accordingly before reentering the guest.

Ok, thanks!

Paolo
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