linux-kernel - Re: [PATCH 03/16] KVM-HDR: KVM Userspace registering ioctl

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Message-ID: <1296044072.15920.48.camel@mothafucka.localdomain>
Date:	Wed, 26 Jan 2011 10:14:32 -0200
From:	Glauber Costa <glommer@...hat.com>
To:	Avi Kivity <avi@...hat.com>
Cc:	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	aliguori@...ibm.com
Subject: Re: [PATCH 03/16] KVM-HDR: KVM Userspace registering ioctl

On Wed, 2011-01-26 at 13:12 +0200, Avi Kivity wrote:
> On 01/24/2011 08:06 PM, Glauber Costa wrote:
> > KVM, which stands for KVM Virtual Memory (I wanted to call it KVM Virtual Mojito),
> > is a piece of shared memory that is visible to both the hypervisor and the guest
> > kernel - but not the guest userspace.
> >
> > The basic idea is that the guest can tell the hypervisor about a specific
> > piece of memory, and what it expects to find in there. This is a generic
> > abstraction, that goes to userspace (qemu) if KVM (the hypervisor) can't
> > handle a specific request, thus giving us flexibility in some features
> > in the future.
> >
> > KVM (The hypervisor) can change the contents of this piece of memory at
> > will. This works well with paravirtual information, and hopefully
> > normal guest memory - like last update time for the watchdog, for
> > instance.
> >
> > This patch contains the header part of the userspace communication implementation.
> > Userspace can query the presence/absence of this feature in the normal way.
> > It also tells the hypervisor that it is capable of handling - in whatever
> > way it chooses, registrations that the hypervisor does not know how to.
> > In x86, only user so far, this mechanism is implemented as generic userspace
> > msr exit, that could theorectically be used to implement msr-handling in
> > userspace.
> >
> > I am keeping the headers separate to facilitate backports to people
> > who wants to backport the kernel part but not the hypervisor, or the other way around.
> >
> 
> Again the protocol is not specified.  How about starting from 
> Documentation/kvm/api.txt so we don't have to guess?
I will do that in the next version, if the idea is not shoot up
completely.

> 
> > diff --git a/include/linux/kvm.h b/include/linux/kvm.h
> > index ea2dc1a..5cc4fe8 100644
> > --- a/include/linux/kvm.h
> > +++ b/include/linux/kvm.h
> > @@ -161,6 +161,7 @@ struct kvm_pit_config {
> >   #define KVM_EXIT_NMI              16
> >   #define KVM_EXIT_INTERNAL_ERROR   17
> >   #define KVM_EXIT_OSI              18
> > +#define KVM_EXIT_X86_MSR_OP	  19
> 
> >
> >   /*
> > @@ -541,6 +551,7 @@ struct kvm_ppc_pvinfo {
> >   #define KVM_CAP_PPC_GET_PVINFO 57
> >   #define KVM_CAP_PPC_IRQ_LEVEL 58
> >   #define KVM_CAP_ASYNC_PF 59
> > +#define KVM_CAP_REGISTER_MEM_AREA 60
> 
> These two seem completely unrelated.

Thanks, will put them in the right place.


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