linux-kernel - Re: [PATCH 01/16] KVM-HDR: register KVM basic header infrastructure

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Message-ID: <4D41659B.1010706@redhat.com>
Date:	Thu, 27 Jan 2011 14:31:23 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Glauber Costa <glommer@...hat.com>
CC:	Anthony Liguori <anthony@...emonkey.ws>, kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org, aliguori@...ibm.com
Subject: Re: [PATCH 01/16] KVM-HDR: register KVM basic header infrastructure

On 01/26/2011 07:49 PM, Glauber Costa wrote:
> >
> >  If type becomes implied based on the MSR number, you'd get the best of
> >  both worlds, no?
> >
> >  I do think advertising features in CPUID is nicer than writing to an MSR
> >  and then checking for an ack in the memory region.
> Fine. But back to the point, I think the reasoning here is that I see
> all those areas as just a single feature, shared data.

That's not a feature.  kvmclock and apf are features.

> >
> >  I do think having a standard mechanism for small regions of shared
> >  memory between the hypervisor and guest is a reasonable thing to do.
>
> Through what I am proposing, or through something else? (including
> slight variations)
>

I'd like to keep the current way of doing things.  Helpers in the guest 
and host to consolidate code are fine, but there's no need to impact the 
ABI.

e.g.

     kvm_register_feature_msr(u32 msr, u64 alignment, struct cpuid_bit 
*feature, int (*callback)(struct kvm_vcpu *vcpu, u64 value))

will install handlers for wrmsr and rdmsr, and declare the msr for 
save/restore, tell the wrmsr handler which cpuid bit allows exposing the 
msr, and registers a callback for when the msr is written by the guest.

-- 
error compiling committee.c: too many arguments to function

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