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

[Jan Kiszka]

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.

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

Jan

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