Re: KVM 29: Page fault in kernel mode while booting GNU/kFreeBSD

[Aurelien Jarno <aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org>]

On Sun, Jul 15, 2007 at 09:23:31AM +0300, Avi Kivity wrote:
> Can you bisect kvm to find the offending commit?  Basically, you do a
> 
>   git clone git://git.kernel.org/pub/scm/linux/kernel/git/avi/kvm.git
>   cd kvm
>   git bisect start drivers/kvm/
>   bit bisect bad kvm-29
>   git bisect good kvm-28
> 
> git will check out a test candidate; go to your kvm userspace directory 
> and do
> 
>   make -C kernel sync LINUX=/path/to/the/kvm/git/directory
>   make -C kernel
>   sudo make -C kernel install
> 
> reload the module, test, and issue 'git bisect good' or 'git bisect bad' 
> according to the result.  As there are only 25 commits you should be 
> done in 5 cycles.
> 

And the result is:

commit ba9c20c048726037664d303362b688759fdf6e9d
Author: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
Date:   Tue Jun 19 22:41:20 2007 +0200

    KVM: Fix x86 emulator writeback
    
    When the old value and new one are the same the emulator skips the
    write; this is undesirable when the destination is a MMIO area and the
    write shall be performed regardless of the previous value. This
    optimization breaks e.g. a Linux guest APIC compiled without
    X86_GOOD_APIC.
    
    Remove the check and perform the writeback stage in the emulation unless
    it's explicitly disabled (currently push and some 2 bytes instructions
    may disable the writeback).
    
    Signed-Off-By: Luca Tettamanti <kronos.it-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
    Signed-off-by: Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>


I have tried to revert this patch directly into kvm-29, and it also
fixes the problem.

-- 
  .''`.  Aurelien Jarno	            | GPG: 1024D/F1BCDB73
 : :' :  Debian developer           | Electrical Engineer
 `. `'   aurel32-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org         | aurelien-rXXEIb44qovR7s880joybQ@public.gmane.org
   `-    people.debian.org/~aurel32 | www.aurel32.net

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