On Tue, Aug 2, 2016 at 12:19 AM, sepanta s <sapanta...@gmail.com> wrote:
>
>
> On Sat, Jul 23, 2016 at 3:49 PM, sepanta s <sapanta...@gmail.com> wrote:
>
>>
>>>> Hi,
>>>> Is there any sample code which I can undestand how to capture the
>>>> events on the gfns which have p2m_ram_shared enabled ?
>>>> I couldn't find any ... .
>>>> I would be grateful if any help , as there is not any documents through
>>>> net to use :(
>>>>
>>>>
>>> Should I just set the ring_page as the pages which are shared and mark
>>>> them read-only, then capture the write events?
>>>>
>>>
>>> Not sure what ring_page you are talking about, but if you mark the pages
>>> read-only with mem_access you will get notifications for events that lead
>>> to unsharing with p2m_ram_shared type pages as well.
>>>
>>
>> There was a function in mem-sharing.c which is intended to announce the
>> failed unshared pages. It is "mem_sharing_notify_enomem" .
>> I added "mem_sharing_notify_unshare" as a new function and call it in
>> also XEN_DOMCTL_VM_EVENT_OP_UNSHARING and "HVM_PARAM_USHARING_RING_PFN".
>> I also added the required codes in /xen/common/vm_event.c and
>> /tools/libxc/xc_vm_event so as
>> I have added a new event for the unsharing actions of a page.
>> Then, I wrote a sample code line xen-access and create a ring for the
>> pages of a domain and listen to unshared events of it.
>>
>>>
>>>> BTW, I added a function called mem_sharing_notify_unshare to
>>>> mem_sharing.c and added it to __mem_sharing_unshare_page at this part:
>>>>
>>>> *if ( p2m_change_type_one(d, gfn, p2m_ram_shared, p2m_ram_rw) )*
>>>> *{*
>>>> *gdprintk(XENLOG_ERR, "Could not change p2m type d %hu gfn %lx.\n", *
>>>> *d->domain_id, gfn);*
>>>> *BUG();*
>>>> *}else {*
>>>>
>>>>
>>>> * mem_sharing_notify_unshare(d,gfn.0);*
>>>> *}*
>>>>
>>>>
>>> IMHO this duplicates a lot of what mem_access does already, I don't
>>> think there is a need for a separate notification on another ring.
>>>
>>>
>> You are right, xen-access should work but I couldn't change its code and
>> couldn't get the mem-access events.
>> I just added the above function to be sure that unsharing a page happens
>> and works fine. Because I couldn't get the access requests on shared-pages
>> of a vm.
>> In xen-access, Instead of setting all the pages' default access to rx , I
>> just call xc_set_mem_access for the pages with p2m_ram_shared and assign rx
>> as the default access but there is no requests on this ring.
>>
>>>
>>
>> So by having a vm event channel listening to unsharing event, I can see
>>>> the notification in xen-access . To do so, I
>>>> have used vm_event_enable which uses HVM_PARAM_SHARING_RING_PFN .
>>>> But, when I used memshrtool to share all the pages of two vms - my vm1
>>>> and its clone vm2 .
>>>> About 900 MB of the ram is shared but there are a lot of unshared
>>>> events happening.
>>>>
>>>
>>> Yes, I would say that's expected.
>>>
>>
>>>
>>>> When I do the sharing one more time, there is not any pages unshared as
>>>> the total number of shared pages stay the same.
>>>>
>>>
>>> Well, if you let the domain run for a while after sharing, then you do
>>> the sharing like that again you are likely going to crash the VM.
>>>
>>>
>>>> Seems no unsharing is done as the number of shared pages are the same.
>>>> Does any page fault triggers when a write operation is done on a shared
>>>> page among two vms ?
>>>>
>>>
>>> I would guess the the VM crashed and that's why you don't see any more
>>> unsharing at that point.
>>>
>> Yes it was crashed as I checked it.
>> The scenario of sharing is I use:
>> I pause the origin VM and then run memshrtool on origin VM and clone VM.
>> After sharing all the pages between these two VMs,Clone VM seems to be
>> inaccessible. The clone seems to work as the attached photo shows, its cpu
>> time increases and it exceeds the dom0 cpu time but when I use gvncviewer
>> to see the GUI of the Clone VM, the mouse or keyboard don't work. (origin
>> VM is ubunut-64-1 and clone VM is ubuntu-64-clone-1). Is there anything I
>> have missed in sharing between two VMs?
>>
>> [image: Inline image 2]
>>
>
> Can someone help please ? still have problem with the machine .
> is it because sharing is not based on content?
>
>
Well, the emulated device contexts probably get all messed up when you just
clone over the memory of the domain and that's why they don't work. The
only way I got this to work is by doing a save/restore of the origin domain
before doing the memory sharing.
Tamas
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