Re: QEMU, MCE, unpoison memory address across reboot

[Avi Kivity <avi@redhat.com>]

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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