[Qemu-devel] Re: [RFC 2/2] KVM, MCE, unpoison memory address across reboot

[Huang Ying]

On Fri, 2010-12-31 at 17:10 +0800, Jan Kiszka wrote:
> Am 31.12.2010 06:22, Huang Ying wrote:
> > In Linux kernel HWPoison processing implementation, the virtual
> > address in processes mapping the error physical memory page is marked
> > as HWPoison.  So that, the further accessing to the virtual
> > address will kill corresponding processes with SIGBUS.
> > 
> > If the error physical memory page is used by a KVM guest, the SIGBUS
> > will be sent to QEMU, and QEMU will simulate a MCE to report that
> > memory error to the guest OS.  If the guest OS can not recover from
> > the error (for example, the page is accessed by kernel code), guest OS
> > will reboot the system.  But because the underlying host virtual
> > address backing the guest physical memory is still poisoned, if the
> > guest system accesses the corresponding guest physical memory even
> > after rebooting, the SIGBUS will still be sent to QEMU and MCE will be
> > simulated.  That is, guest system can not recover via rebooting.
> > 
> > In fact, across rebooting, the contents of guest physical memory page
> > need not to be kept.  We can allocate a new host physical page to
> > back the corresponding guest physical address.
> > 
> > This patch fixes this issue in QEMU-KVM via calling qemu_ram_remap()
> > to clear the corresponding page table entry, so that make it possible
> > to allocate a new page to recover the issue.
> > 
> > Signed-off-by: Huang Ying <address@hidden>
> > ---
> >  kvm.h             |    2 ++
> >  qemu-kvm.c        |   37 +++++++++++++++++++++++++++++++++++++
> 
> What's missing in upstream to make this a uq/master patch? We are still
> piling up features and fixes in qemu-kvm* that should better target
> upstream directly. That's work needlessly done twice.

OK. I will do that. Just based on uq/master is sufficient to make it an
upstream patch?

> Is this infrastructure really arch-independent? Will there be other
> users besides x86? If not, better keep it in target-i386/kvm.c.

No.  It is used only in x86.  I will move it into target-i386/kvm.c.

Best Regards,
Huang Ying