Re: 64 bit Intel HVM Weirdness - setjmp\longjump fp exception in Xen, not on real hardware or AMD HVM

[Allan Graves <allan.graves@oracle.com>]

Keir -

Hmm... according to /sys/hypervisor/version, I'm running 3.4.0.

Is there a reasonable chance this is fixed in 3.4.1?  I haven't seen 
anything in the changelogs...


Allan



Keir Fraser wrote:
> What version of Xen are you using? This bug may be fixed in Xen 3.3.2 and
> Xen 3.4.1.
>
>  -- Keir
>
> On 30/10/2009 01:23, "Allan Graves" <allan.graves@oracle.com> wrote:
>
>   
>> (Please excuse double posting - I was told xen-users was not the right
>> list, to put it on xen-devel, as it was not a technical support query,
>> but an issue.)
>>
>>
>> The following program will crash with a fp exception on an INTEL 64 bit
>> HVM domU only:
>> #include <setjmp.h>
>> jmp_buf env; main() { if(setjmp(env)) return; longjmp(env, 1); }
>>
>>
>> This can be seen using both Linux and Windows 64 bit Guests.
>>
>>
>> My machine is a Core 2 Duo with both VT-D and VT-X extensions enabled.
>> Unfortunately, this is blocking our usage of 64 bit HVM Windows guests.
>>
>> A similar issue was reported in KVM and recently fixed, some of their
>> analysis is below:
>> --------------------------------------------------
>>     
>>>>> It seems that the problem can be reproduced by compiling the
>>>>> following simple program using cygwin's gcc. The program crashes on
>>>>> w2k3-amd64 on kvm-83 on core2-duo, and it does not crash on the
>>>>> same w2k3-amd64 installation on kvm-83 on AMD Phenom.
>>>>>
>>>>> #include <setjmp.h>
>>>>>
>>>>> jmp_buf env; main() { if(setjmp(env)) return; longjmp(env, 1); }
>>>>>
>>>>> The problem seems to be in the instruction ``mov gs,ax'' (Intel
>>>>> syntax) in the longjmp() code. If I let the virtual machine execute
>>>>> the instruction, the program crashes. However, if I step over the
>>>>> instruction using the vs2008 debugger, the program completes
>>>>> without crashing. Thus, I think that this is the instruction that
>>>>> Avi is looking for, but I don't know how to proceed from here.
>>>>> -------------------------------------------------------
>>>>>           
>> http://markmail.org/message/owy3x7pf6oywdx5e#query:+page:1+mid:spz6vmdothb2njf
>> b+state:results 
>>
>>
>>
>> Anyone have a solution to this? :)
>>
>> Allan
>>
>>
>>
>>
>>
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>> Xen-devel mailing list
>> Xen-devel@lists.xensource.com
>> http://lists.xensource.com/xen-devel
>>     
>
>
>