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Subject: RE: possible CPU bug and request for Intel contacts
Date: Mon, 14 Feb 2005 08:55:05 -0800
Message-ID: <88056F38E9E48644A0F562A38C64FB600400357E@scsmsx403.amr.corp.intel.com>
Thread-Topic: possible CPU bug and request for Intel contacts
Thread-Index: AcUSCA19r+ILkiunSsaMezGFLaoUDwArX5gQ
From: "Pallipadi, Venkatesh" <venkatesh.pallipadi@intel.com>
To: "Ingo Molnar" <mingo@elte.hu>, "Seth, Rohit" <rohit.seth@intel.com>
Cc: "Kirill Korotaev" <dev@sw.ru>, "Linus Torvalds" <torvalds@osdl.org>,
       "Saxena, Sunil" <sunil.saxena@intel.com>,
       "Andrey Savochkin" <saw@sawoct.com>, <linux-kernel@vger.kernel.org>
Sender: linux-kernel-owner@vger.kernel.org
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>-----Original Message-----
>From: Ingo Molnar [mailto:mingo@elte.hu] 
>Sent: Sunday, February 13, 2005 12:10 PM
>To: Seth, Rohit
>Cc: Kirill Korotaev; Linus Torvalds; Saxena, Sunil; Pallipadi, 
>Venkatesh; Andrey Savochkin; linux-kernel@vger.kernel.org
>Subject: Re: possible CPU bug and request for Intel contacts
>
>
>* Seth, Rohit <rohit.seth@intel.com> wrote:
>
>> On a little different note, while running the 4G-4G kernel on our
>> machine, we saw occasional hangs.  Those are root caused to the fact
>> that this kernel was first chaging the stack pointer from virtual
>> stack to kernel and then changing the CR3 to that of kernel.  Any
>> interrupt between these two instructions will result in 
>those hangs as
>> the interruption handler will execute with user's CR3(as the kernel
>> thinks that it is already in kernel because of the value of esp). 
>> Swapping the order, first loading the CR3 with kernel and then
>> switching the stack to kernel fixes this issue.  Venki will generate
>> that patch and send to lkml.
>
>i'm not sure what you mean. Here's the relevant 4:4 code from Fedora:
>
>#define __SWITCH_KERNELSPACE                            \
>...
>        movl %edx, %cr3;                                \
>        movl %ebx, %esp;                                \
>
>i.e. we _first_ load cr3 with the kernel pagetable value, then do we
>switch esp to the real kernel stack.
>

Yes. I verified that and that's the reason I didn't send any patch. But,

the kernel we were using in our testing of this bug, came from some 
earlier version of 4:4 code and had this cr3 switch and esp switch in 
reverse order. 

With the latest kernels there is no issue related to this.

Thanks,
Venki
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