linux-kernel - Re: [Qemu-devel] kvm bug in __rmap_clear

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Date:   Fri, 24 Feb 2017 10:59:51 +0100
From:   Greg KH <gregkh@...uxfoundation.org>
To:     "Herongguang (Stephen)" <herongguang.he@...wei.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Chris Friesen <chris.friesen@...driver.com>,
        "Han, Huaitong" <huaitong.han@...el.com>,
        "hangaohuai@...wei.com" <hangaohuai@...wei.com>,
        stable@...r.kernel.org,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "fangying1@...wei.com" <fangying1@...wei.com>,
        "xudong.hao@...ux.intel.com" <xudong.hao@...ux.intel.com>,
        "qemu-devel@...gnu.org" <qemu-devel@...gnu.org>,
        "wangxinxin.wang@...wei.com" <wangxinxin.wang@...wei.com>,
        "kai.huang@...ux.intel.com" <kai.huang@...ux.intel.com>,
        "rkrcmar@...hat.com" <rkrcmar@...hat.com>,
        "guangrong.xiao@...ux.intel.com" <guangrong.xiao@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [Qemu-devel] kvm bug in __rmap_clear_dirty during live migration

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 VM2’s 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 VM2’s 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.

thanks,

greg k-h