Hi KAZ,
For your latest patch, I am thinking of the following code.
+ /* check whether a page number have been already registered or not */
+ list_for_each_entry(page, &page_offlining, list) {
+ if (page == pg)
+ goto out;
+ }
x86_page_offlining_t e is put into the list. Here, is it "if (e->page == pg)"?
+
+ /* check whether already having attribute 'reserved' */
+ if (pg->count_info & PGC_reserved) {
+ printk(XENLOG_DEBUG "Page offlining: ( %lx ) failure.\n",
+ maddr);
+ return 1;
+ }
+
+ /* add attribute 'reserved' and register the page */
+ get_page(pg, d);
+ pg->count_info |= PGC_reserved;
+
+ e = xmalloc(x86_page_offlining_t);
+ BUG_ON(e == NULL);
+ e->page = pg;
+ list_add(&e->list, &page_offlining);
Since page struct is also a list entry (containing "struct list_head list").
You can pick off from domain page list and put it onto your page_offlining list.
Certainly, the domain may be using it now. You can mark it by using your flag
PGC_reserved first and then do this in the free function. I think this is what
Jiang Yunhong suggested:)
What do you think on those suggestions? PS: in that case,
alloc_bitmap[]/heap[][][]/avail[] should be considered.
For the code piece
+ 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));
+
It seems this mechanism is not efficient enough since the first page is marked
PGC_reserved (but the rest pages in heap(node, zone, j).next are not, the rest
pages can't be used and allocated any more although they are not offlined), and
it didn't solve the potential bug I mentioned.
Moreover, since the original code (i.e. without your patch) just tries to find
a space with an enough order, it just gets the first finding. So it is enough.
However, I am wondering why you don't try to enumerate heap(node, zone, j) to
get the second one ... but directly return "not to be allocated", when the code
finds the first list entry can't meet the requirement?
Thanks.
Shane
-----Original Message-----
From: SUZUKI Kazuhiro [mailto:kaz@xxxxxxxxxxxxxx]
Sent: 2008年12月22日 8:42
To: Jiang, Yunhong
Cc: Wang, Shane; xen-devel@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-devel] [PATCH 0/2] MCA support with page offlining
Hi,
> But I'm a bit confused some changes in this patch.
Sorry, I attached a wrong patch, this is a correct one.
Thanks,
KAZ
Signed-off-by: Kazuhiro Suzuki <kaz@xxxxxxxxxxxxxx>
From: "Jiang, Yunhong" <yunhong.jiang@xxxxxxxxx>
Subject: RE: [Xen-devel] [PATCH 0/2] MCA support with page offlining
Date: Fri, 19 Dec 2008 18:48:11 +0800
> SUZUKI Kazuhiro <mailto:kaz@xxxxxxxxxxxxxx> wrote:
> > Hi Yunhong and Shane,
> >
> > Thank you for your comments and reviews.
> >
> >> For page offlining, It may not be a good way to put the page into an array
> >> but a list.
> >
> > I modified to register offlined pages to a list instead of an array.
> >
> >> I guess the code targets for offlining domain pages only,
> > right? How about free pages and xen pages?
> >> If so, no need to check in the following when allocating
> > free pages, since the offlined pages will not be freed into heap()()().
> >> If not, the following may have a bug.
> >
> > Yes, I assumed that offlining page was needed for domain pages. If xen
> > pages are impacted, then it is enough to crash the Hypervisor, in current
> > implementation.
>
> We have a internal patch for the similar purpose, for page offline caused by
> both #MC or other purpose. We can base our work on your patch if needed.
>
> But I'm a bit confused some changes in this patch.
> In your previous version, if a page is marked as PGC_reserved, it will not be
> allocated anymore. However, in this version, when a page is marked as
> PGC_reserved, it is just not freed, so does that mean the page will not be
> removed from current list? That seems a bit hack for me.
>
> What I think to do is for page offline is:
> a) mark a page as PGC_reserved (or other name like PGC_broken )
> b) If it is free, to step c, otherwise, wait till it is freed by the owner
> and to step c.
> c) Remove the page from the buddy system, motve it to a special and seperated
> list (i.e. not in the heap[][][] anymore), and return other page to the buddy
> allocator.
>
> Some argument is in step b, that if the page is owned by a guest, we can
> replace it with a new page through p2m table, and don't need wait till it is
> freed, we didn't do that currently because it is a bit complex to achieve
> that.
>
> How is your idea on this?
>
> Thanks
> Yunhong Jiang
>
> >
> > I attach an updated patch for xen part which also includes some bug fixes.
> >
> > Thanks,
> > KAZ
> >
> > Signed-off-by: Kazuhiro Suzuki <kaz@xxxxxxxxxxxxxx>
> >
> >
> > From: "Wang, Shane" <shane.wang@xxxxxxxxx>
> > Subject: RE: [Xen-devel] [PATCH 0/2] MCA support with page offlining
> > Date: Tue, 16 Dec 2008 19:10:00 +0800
> >
> >> For page offlining, It may not be a good way to put the page into an array
> >> but a list.
> >>
> >> + pg->count_info |= PGC_reserved;
> >> + page_offlining[num_page_offlining++] = pg;
> >>
> >> I guess the code targets for offlining domain pages only,
> > right? How about free pages and xen pages?
> >> If so, no need to check in the following when allocating
> > free pages, since the offlined pages will not be freed into heap()()().
> >> If not, the following may have a bug.
> >>
> >> + 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)); +
> >> }
> >>
> >> If one free page (not pg) within pg and pg+(1U<<j) is
> > offlined, the range pg~pg+(1U<<j) has the risk to be allocated
> > with that page.
> >>
> >> Shane
> >>
> >> Jiang, Yunhong 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
> >>>>
> >>>> _______________________________________________
> >>>> Xen-devel mailing list
> >>>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >>>> http://lists.xensource.com/xen-devel
> >>> _______________________________________________
> >>> Xen-devel mailing list
> >>> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >>> http://lists.xensource.com/xen-devel
> >>
> >>
> >> _______________________________________________
> >> Xen-devel mailing list
> >> Xen-devel@xxxxxxxxxxxxxxxxxxx
> >> http://lists.xensource.com/xen-devel
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