Re: [Qemu-devel] kvm bug in __rmap_clear_dirty during live migration

[Greg KH]

On Fri, Feb 24, 2017 at 11:00:32AM +0100, Paolo Bonzini wrote:
> 
> 
> On 24/02/2017 10:59, Greg KH wrote:
> > On Fri, Feb 24, 2017 at 05:35:17PM +0800, Herongguang (Stephen) wrote:
> >>
> >>
> >> On 2017/2/24 10:23, Herongguang (Stephen) wrote:
> >>>
> >>>
> >>> On 2017/2/22 22:43, Paolo Bonzini wrote:
> >>>>
> >>>>
> >>>> On 22/02/2017 14:31, Chris Friesen wrote:
> >>>>>>>
> >>>>>>
> >>>>>> Can you reproduce it with kernel 4.8+?  I'm suspecting commmit
> >>>>>> 4e59516a12a6 ("kvm: vmx: ensure VMCS is current while enabling PML",
> >>>>>> 2016-07-14) to be the fix.
> >>>>>
> >>>>> I can't easily try with a newer kernel, the software package we're using
> >>>>> has kernel patches that would have to be ported.
> >>>>>
> >>>>> I'm at a conference, don't really have time to set up a pair of test
> >>>>> machines from scratch with a custom kernel.
> >>>>
> >>>> Hopefully Gaohuai and Rongguang can help with this too.
> >>>>
> >>>> Paolo
> >>>>
> >>>> .
> >>>>
> >>> Yes, we are looking into and testing this.
> >>>
> >>> I think this can result in any memory corruption, if VM1 writes its
> >>> PML buffer into VM2âs VMCS (since sched_in/sched_out notifier of VM1
> >>> is not registered yet), then VM1 is destroyed (hence its PML buffer
> >>> is freed back to kernel), after that, VM2 starts migration, so CPU
> >>> logs VM2âs dirty GFNS into a freed memory, results in any memory corruption.
> >>>
> >>> As its severity, this commit (http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/commit/?id=4e59516a12a6ef6dcb660cb3a3f70c64bd60cfec)
> >>> is eligible to back port to kernel stable.
> >>
> >> Hi, Greg, can you cherry pick commit 4e59516a12a6ef6dcb660cb3a3f70c64bd60cfec to 4.4-y?
> > 
> > If the KVM maintainers say it is ok to do so, yes, I will.
> 
> Yes, he beat me by minutes. :)

Heh, ok, I'll go add it to the recently-announced 4.4.52-rc1 release.

thanks,

greg k-h