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RE: [Xen-devel] [PATCH 0/2] MCA support with page offlining

Some clarification, Susuzi,  I just want some discussion of how to enhance the 
MCA support and not against the xen part patch, which has not much change to 
current logicl. (The  kernel part is new and may depends on the discussion).
Hope feedback from you and the community.

Yunhong Jiang

xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
> xen-devel-bounces@xxxxxxxxxxxxxxxxxxx <> wrote:
>> Hi all,
>> I had posted about MCA support for Intel64 before. It had only a
>> function to log the MCA error data received from hypervisor.
> http://lists.xensource.com/archives/html/xen-devel/2008-09/msg0
> 0876.html
>> I attach patches that support not only error logging but also Page
>> Offlining function. The page where an MCA occurs will offline and not
>> reuse. A new flag 'PGC_reserved' was added in page count_info to mark the
>> impacted page. 
>> I know that it is better to implement the page offlining for general
>> purpose, but I implemented for MCA specialized in this first step.
> Maybe the MCA page offline is a bit different to normal page
> offline requirement, so take it as first step maybe a good choice :)
> As for your current page_offlining, I'm not sure why the
> PGC_reserved page should not be freed? Also, for following
> code, will that make the heap(node, zone, j) can't be
> allocated anymore? Maybe we can creat a special list to hold
> all those pages and remove them from the heap list?
> +                if ( !list_empty(&heap(node, zone, j)) ) {
> +                    pg = list_entry(heap(node, zone, j).next,
> struct page_info, list);
> +                    if (!(pg->count_info & PGC_reserved))
> +                        goto found;
> +                    else
> +                        printk(XENLOG_DEBUG "Page %p(%lx) is
> not to be allocated.\n",
> +                               pg, page_to_maddr(pg)); +
>> And I also implement the MCA handler of Dom0 which support to shutdown
>> the remote domain where a MCA occurred. If the MCA occurred on a DomU,
>> Dom0 notifies it to the DomU. When the notify is failed, Dom0 calls
>> SCHEDOP_remote_shutdown hypercall.
>> [1/2] xen part: mca-support-with-page-offlining-xen.patch
> We are not sure we really need pass all #MC information to
> dom0 firstly, and let dom0 to notify domU. Xen should knows
> about everything, so it may have knowledge to decide inject
> virtual #MC to guest or not. Of course, this does not impact
> your patch.
>> [2/2] linux/x86_64 part: mca-support-with-page-offlining-linux.patch
> As for how to inject virtual #MC to guest (including dom0), I
> think we need consider following point:
> a) Benefit from reusing guest #MC handler's . #MC handler is
> well known difficult to test, and the native guest handler may
> have been tested more widely. Also #MC handler improves as
> time going-on, reuse guest's MCA handler share us those improvement.
> b) Maintain the PV handler to different OS version may not so
> easy, especially as hardware improves, and kernel may have
> better support for error handling/containment.
> c) #MC handler may need some model specific information to
> decide the action, while guest (not dom0) has virtualized
> CPUID information.
> d) Guest's MCA handler may requires the physical information
> when the #MC hapen, like the CPU number the #MC happens.
> e) For HVM domain, PV handler will be difficult (considering
> Windows guest).
> And we have several option to support virtual #MC to guest:
> Option 1 is what currently implemented. A PV #MC handler is
> implemented in guest. This PV handler gets MCA information
> from Xen HV through hypercall, including MCA MSR value, also
> some additional information, like which physical CPU the MCA
> happened. Option 1 will help us on issue d), but we need main
> a PV handler, and can't get benifit from native handler. Also
> it does not resolve issue c) quite well.
> option 2, Xen will provide MCA MSR virtualization so that
> guest's native #MC handler can run without changes. It can
> benifit from guest #MC handler, but it will be difficult to
> get model specific information, and has no physical information.
> Option 3 uses a PV #MC handler for guest as option 1, but
> interface between Xen/guest is abstract event, like offline
> offending page, terminate current execution context etc. This
> should be straight forward for Linux, but may be difficult to
> Windows and other OS.
> Currently we are considering option 2 to provide MCA MSR
> virtualization to guest, and dom0 can also benifit from such
> support (if guest has different CPUID as native, we will
> either keep guest running, or kill guest based on error code).
> Of course, current mechanism of passing MCA information from
> xen to dom0 will still be useful, but that will be used for
> logging purpose or for Correcatable Error. How do you think about this?
> Thanks
> Yunhong Jiang
>> Signed-off-by: Kazuhiro Suzuki <kaz@xxxxxxxxxxxxxx>
>> Thanks,
>> KAZ
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