linux-kernel - Re: kvm: how big is type?

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Date:	Mon, 28 Apr 2008 18:23:52 +0300
From:	Izik Eidus <izike@...ranet.com>
To:	Avi Kivity <avi@...ranet.com>
CC:	Harvey Harrison <harvey.harrison@...il.com>,
	LKML <linux-kernel@...r.kernel.org>,
	kvm-devel <kvm-devel@...ts.sourceforge.net>
Subject: Re: kvm: how big is type?

Avi Kivity wrote:
> Harvey Harrison wrote:
>> arch/x86/kvm/x86.c:3484:25: warning: cast truncates bits from constant
>> value (100 becomes 0)
>> arch/x86/kvm/x86.c:3510:24: warning: cast truncates bits from constant
>> value (100 becomes 0)
>>
>> The problem:
>>         cseg_desc.type &= ~(1 << 8); //clear the B flag
>>         nseg_desc.type |= (1 << 8);
>>
>> type is a 4-bit bitfield on x86....please look into this.
>>
>>   
> 
> I think it ought to be (1 << 1), not (1 << 8), as it refers to the
> "busy" bit of the task type.  Izik?
> 
> 
>From cf6e76c69a38a983df0c84a3dcc2336042eb3436 Mon Sep 17 00:00:00 2001
From: Izik Eidus <izike@...ranet.com>
Date: Mon, 28 Apr 2008 18:16:08 +0300
Subject: [PATCH] KVM: x86: task switch: fix wrong bit setting for the busy flag.
 the busy bit is in offset of 1 inside type and not in 8.

Signed-off-by: Izik Eidus <izike@...ranet.com>
---
 arch/x86/kvm/x86.c |    4 ++--
 1 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 0ce5563..5c360bb 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3481,7 +3481,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
 	}
 
 	if (reason == TASK_SWITCH_IRET || reason == TASK_SWITCH_JMP) {
-		cseg_desc.type &= ~(1 << 8); //clear the B flag
+		cseg_desc.type &= ~(1 << 1); //clear the B flag
 		save_guest_segment_descriptor(vcpu, tr_seg.selector,
 					      &cseg_desc);
 	}
@@ -3507,7 +3507,7 @@ int kvm_task_switch(struct kvm_vcpu *vcpu, u16 tss_selector, int reason)
 	}
 
 	if (reason != TASK_SWITCH_IRET) {
-		nseg_desc.type |= (1 << 8);
+		nseg_desc.type |= (1 << 1);
 		save_guest_segment_descriptor(vcpu, tss_selector,
 					      &nseg_desc);
 	}
-- 
1.5.3.6


-- 
woof.
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