Re: [Qemu-devel] DOS VM problem with QEMU-KVM and newer kernels

[Gleb Natapov]

On Tue, Apr 17, 2012 at 08:04:16AM +0200, Gerhard Wiesinger wrote:
> On 15.04.2012 11:44, Avi Kivity wrote:
> >On 04/12/2012 09:32 PM, Gerhard Wiesinger wrote:
> >>Hello,
> >>
> >>I'm having problems with recents kernels and qemu-kvm with a DOS VM:
> >>TD286
> >>System: Bad selector: 0007
> >>System: Bad selector: 0D87
> >>System: Bad selector: 001F
> >>System: Bad selector: 0007
> >>GP at 0020 21D4 EC 0DC4
> >>Error 269 loading D:\BP\BIN\TD286.EXE into extended memory
> >>
> >>Another 286 DOS Extender application also rises a general protection
> >>fault:
> >>GP at 0020 18A1 CODE 357C
> >>
> >>Doesn't depend on the used DOS memory manager and is always
> >>reproduceable.
> >>
> >>Depends only on kernel version and not qemu-kvm and seabios (tried to
> >>bisect it without success):
> >># NOK: Linux 3.3.1-3.fc16.x86_64 #1 SMP Wed Apr 4 18:08:51 UTC 2012
> >>x86_64 x86_64 x86_64 GNU/Linux
> >># NOK: Linux 3.2.10-3.fc16.x86_64 #1 SMP Thu Mar 15 19:39:46 UTC 2012
> >>x86_64 x86_64 x86_64 GNU/Linux
> >># OK: Linux 3.1.9-1.fc16.x86_64 #1 SMP Fri Jan 13 16:37:42 UTC 2012
> >>x86_64 x86_64 x86_64 GNU/Linux
> >># OK: Linux 2.6.41.9-1.fc15.x86_64 #1 SMP Fri Jan 13 16:46:51 UTC 2012
> >>x86_64 x86_64 x86_64 GNU/Linux
> >>
> >>CPU is an AMD one.
> >>
> >>Any ideas how to fix it again?
> >>Any switches which might help?
> >>
> >
> >The trigger is probably
> >
> >>commit f1c1da2bde712812a3e0f9a7a7ebe7a916a4b5f4
> >>Author: Jan Kiszka<address@hidden>
> >>Date:   Tue Oct 18 18:23:11 2011 +0200
> >>
> >>     KVM: SVM: Keep intercepting task switching with NPT enabled
> >>
> >>     AMD processors apparently have a bug in the hardware task switching
> >>     support when NPT is enabled. If the task switch triggers a NPF, we can
> >>     get wrong EXITINTINFO along with that fault. On resume, spurious
> >>     exceptions may then be injected into the guest.
> >>
> >>     We were able to reproduce this bug when our guest triggered #SS
> >>and the
> >>     handler were supposed to run over a separate task with not yet touched
> >>     stack pages.
> >>
> >>     Work around the issue by continuing to emulate task switches even in
> >>     NPT mode.
> >>
> >>     Signed-off-by: Jan Kiszka<address@hidden>
> >>     Signed-off-by: Marcelo Tosatti<address@hidden>
> >Although it's not the patch's direct fault - it simply exposed an
> >existing bug in kvm.
> >
> >Things to try:
> >- revert the patch with a newer kernel
> >- try 3.4-rc2 which has some task switch fixes from Kevin; if you want a
> >Fedora kernel, use rawhide's [2]
> >- post traces [1]
> >
> >Jan, Joerg, was an AMD erratum published for the bug?
> >
> >[1] http://www.linux-kvm.org/page/Tracing
> >[2]
> >http://mirrors.kernel.org/fedora/development/rawhide/x86_64/os/Packages/k/kernel-3.4.0-0.rc2.git2.1.fc18.x86_64.rpm
> >
> 
> Hello Avi,
> 
> Status is as follows:
> 1.) Kernel 3.4.x DIDN'T fix the problem
> 2.) Reverting f1c1da2bde712812a3e0f9a7a7ebe7a916a4b5f4 FIXED the problem.
> 
> So the bug is still in 3.2., 3.3, 3.4rc present and a possible fix
> doesn't work. Should be fixed in 3.4 release.
> 
> How to proceed further?
> 
Can you post image of your VM somewhere?

--
                        Gleb.