>
>
>> 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]
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