Re: QEMU, MCE, unpoison memory address across reboot

Avi Kivity
2010-12-26T12:27:58Z

On 12/23/2010 04:28 PM, Marcelo Tosatti wrote:
> On Wed, Dec 22, 2010 at 10:52:51AM +0800, 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 invoke the unpoison
> > mechanism implemented in Linux kernel 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<ying.huang@intel.com>
>
> > +struct HWPoisonPage;
> > +typedef struct HWPoisonPage HWPoisonPage;
> > +struct HWPoisonPage
> > +{
> > + void *vaddr;
> > + QLIST_ENTRY(HWPoisonPage) list;
> > +};
> > +
> > +static QLIST_HEAD(hwpoison_page_list, HWPoisonPage) hwpoison_page_list =
> > + QLIST_HEAD_INITIALIZER(hwpoison_page_list);
> > +
> > +static void kvm_unpoison_all(void *param)
> > +{
> > + HWPoisonPage *page, *next_page;
> > + unsigned long address;
> > + KVMState *s = param;
> > +
> > + QLIST_FOREACH_SAFE(page,&hwpoison_page_list, list, next_page) {
> > + address = (unsigned long)page->vaddr;
> > + QLIST_REMOVE(page, list);
> > + kvm_vm_ioctl(s, KVM_UNPOISON_ADDRESS, address);
> > + qemu_free(page);
> > + }
> > +}
>
> Can't you free and reallocate all guest memory instead, on reboot, if
> there's a hwpoisoned page? Then you don't need this interface.
>

Alternatively, MADV_DONTNEED? We already use it for ballooning.

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