Re: QEMU, MCE, unpoison memory address across reboot

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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@xxxxxxxxx>

>  +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.

--
error compiling committee.c: too many arguments to function

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