linux-kernel - Re: [PATCH V2] Documentation/kvm: Update cpuid documentation for steal time and pv eoi

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Message-ID: <523168E3.10405@linux.vnet.ibm.com>
Date:	Thu, 12 Sep 2013 12:40:27 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	"Michael S. Tsirkin" <mst@...hat.com>
CC:	Gleb Natapov <gleb@...hat.com>,
	Paolo Bonzini <pbonzini@...hat.com>, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
	Rob Landley <rob@...dley.net>, mtosatti@...hat.com
Subject: Re: [PATCH V2] Documentation/kvm: Update cpuid documentation for
 steal  time and pv eoi

On 09/12/2013 11:14 AM, Michael S. Tsirkin wrote:
> On Wed, Sep 04, 2013 at 02:18:46PM +0530, Raghavendra K T wrote:
[...]
>>   ------------------------------------------------------------------------------
>> +KVM_FEATURE_STEAL_TIME             ||     5 || Steal time available at msr
>> +                                   ||       || 0x4b564d03. The feature is enabled
>> +                                   ||       || by guest when host has schedstat
>> +                                   ||       || or task delay accounting support.
>
> Well I think we really should be documenting the host/guest interface
> here.
> After all it starts out
> 	A guest running on a kvm host, can check some of its features using
> 	cpuid.
> And guests really should not try to guess whether host
> has schedstat or task delay accounting support based on this bit.
> So I would just say:
> 	"steal time can be enabled by writing to msr 0x4b564d02"
> just like async pf.
>

It makes sense. will stick to the above line.

>
>> +------------------------------------------------------------------------------
>> +KVM_FEATURE_PV_EOI                 ||     6 || overrides the generic EOI
>> +                                   ||       || implementation with a
>> +                                   ||       || paravirtualized version. Available
>> +                                   ||       || at msr 0x4b564d04.
>
> Actually there's no override: guest can still use the
> standard EOI even if PV EOI MSR is enabled.
>
> There's a detailed explanation of PV EOI in
> Documentation/virtual/kvm/msr.txt
> I think the following would be enough:
>
> 	"paravirtualized end of interrupt handler can be enabled by writing to msr 0x4b564d04"
>

Okay.
Thanks Michael.

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