linux-kernel - [PATCH] KVM: fix calculation of initial value of rdx register

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Message-Id: <20061106131502.BD90D2500A7@cleopatra.q>
Date:	Mon, 06 Nov 2006 13:15:02 -0000
From:	Avi Kivity <avi@...ranet.com>
To:	kvm-devel@...ts.sourceforge.net
Cc:	Christian Hesse <mail@...thworm.de>, linux-kernel@...r.kernel.org,
	akpm@...l.org
Subject: [PATCH] KVM: fix calculation of initial value of rdx register

On bootup, the rdx register contains information about the processor.  The
function which calculates this value has the bugs:

 - missing 'cpuid' to get the value from the processor
 - missing register clobber caused a miscompilation in some circumstances
 - we shouldn't return a value that depends on the current processor in 
   case we migrate

In any case nobody looks at the value, so just return a generic P6
identifier.

Thanks to Christian Hesse <mail@...thworm.de> for debugging help.

Signed-off-by: Avi Kivity <avi@...ranet.com>

Index: linux-2.6/drivers/kvm/kvm_main.c
===================================================================
--- linux-2.6.orig/drivers/kvm/kvm_main.c
+++ linux-2.6/drivers/kvm/kvm_main.c
@@ -1052,12 +1052,7 @@ static void set_cr8(struct kvm_vcpu *vcp
 
 static u32 get_rdx_init_val(void)
 {
-	u32 val;
-
-	asm ("movl $1, %%eax \n\t"
-	     "movl %%eax, %0 \n\t" : "=g"(val) );
-	return val;
-
+	return 0x600; /* P6 family */
 }
 
 static void fx_init(struct kvm_vcpu *vcpu)
-
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