linux-kernel - RE: [kvm-devel] [PATCH 2/3] Refactor hypercall infrastructure (v3)

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Date:	Mon, 17 Sep 2007 14:56:50 -0700
From:	"Nakajima, Jun" <jun.nakajima@...el.com>
To:	"Anthony Liguori" <aliguori@...ibm.com>,
	<kvm-devel@...ts.sourceforge.net>
Cc:	"Zachary Amsden" <zach@...are.com>, <linux-kernel@...r.kernel.org>,
	"Avi Kivity" <avi@...ranet.com>,
	"Jeremy Fitzhardinge" <jeremy@...p.org>
Subject: RE: [kvm-devel] [PATCH 2/3] Refactor hypercall infrastructure (v3)

Anthony Liguori wrote:
> This patch refactors the current hypercall infrastructure to better
support
> live 
> migration and SMP.  It eliminates the hypercall page by trapping the
UD
> exception that would occur if you used the wrong hypercall instruction
for the
> underlying architecture and replacing it with the right one lazily.
> 
> It also introduces the infrastructure to probe for hypercall available
via
> CPUID leaves 0x40000000.  CPUID leaf 0x40000001 should be filled out
by
> userspace.
> 
> A fall-out of this patch is that the unhandled hypercalls no longer
trap to
> userspace.  There is very little reason though to use a hypercall to
> communicate 
> with userspace as PIO or MMIO can be used.  There is no code in tree
that uses
> userspace hypercalls.
> 
> Signed-off-by: Anthony Liguori <aliguori@...ibm.com>
> 
> diff --git a/include/linux/kvm_para.h b/include/linux/kvm_para.h
> index 3b29256..cc5dfb4 100644
> --- a/include/linux/kvm_para.h
> +++ b/include/linux/kvm_para.h
> @@ -1,73 +1,110 @@
>  #ifndef __LINUX_KVM_PARA_H
>  #define __LINUX_KVM_PARA_H
> 
> -/*
> - * Guest OS interface for KVM paravirtualization
> - *
> - * Note: this interface is totally experimental, and is certain to
change
> - *       as we make progress.
> +/* This CPUID returns the signature 'KVMKVMKVM' in ebx, ecx, and edx.
It
> + * should be used to determine that a VM is running under KVM.

<snip>

> +
> +static inline int kvm_para_available(void)
> +{
> +	unsigned int eax, ebx, ecx, edx;
> +	char signature[13];
> +
> +	cpuid(KVM_CPUID_SIGNATURE, &eax, &ebx, &ecx, &edx);
> +	memcpy(signature + 0, &ebx, 4);
> +	memcpy(signature + 4, &ecx, 4);
> +	memcpy(signature + 8, &edx, 4);
> +	signature[12] = 0;
> +
> +	if (strcmp(signature, "KVMKVMKVM") == 0)

> +		return 1;
> +
> +	return 0;
> +}

I think we should compare 12 characters (not just 9, as far as my eyes
tell), and can we use some cute one, like "FantasticKVM"? ;-)

Jun
---
Intel Open Source Technology Center
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