Re: [Xen-devel] [PATCH v3 0/3] map grant refs at pfn = mfn

[Thomas Leonard <talex5@xxxxxxxxx>]

On 6 August 2014 14:35, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Wed, 6 Aug 2014, Thomas Leonard wrote:
>> On 1 August 2014 19:12, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>> > On 1 August 2014 18:16, Stefano Stabellini
>> > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >> On Fri, 1 Aug 2014, Thomas Leonard wrote:
>> >>> On 1 August 2014 18:01, Stefano Stabellini
>> >>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >>> > On Fri, 1 Aug 2014, Thomas Leonard wrote:
>> >>> >> On 1 August 2014 17:25, Stefano Stabellini
>> >>> >> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >>> >> > On Fri, 1 Aug 2014, Julien Grall wrote:
>> >>> >> >> On 01/08/14 17:16, Thomas Leonard wrote:
>> >>> >> >> > On 1 August 2014 16:13, Stefano Stabellini
>> >>> >> >> > <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >>> >> >> > > On Fri, 1 Aug 2014, Thomas Leonard wrote:
>> >>> >> >> > > > On 24/07/14 14:30, Stefano Stabellini wrote:
>> >>> >> >> > > > > Hi all,
>> >>> >> >> > > > > this patch series introduces a second p2m mapping of grant 
>> >>> >> >> > > > > reference
>> >>> >> >> > > > > on
>> >>> >> >> > > > > ARM at guest physical address == machine address of the 
>> >>> >> >> > > > > grant ref.  It
>> >>> >> >> > > > > is safe because dom0 is already mapped 1:1. We export
>> >>> >> >> > > > > XENFEAT_grant_map_identity to signal the guest that this 
>> >>> >> >> > > > > second p2m
>> >>> >> >> > > > > mapping is
>> >>> >> >> > > > > available.
>> >>> >> >> > > > >
>> >>> >> >> > > > > One reason for wanting the second p2m mapping is to avoid 
>> >>> >> >> > > > > tracking mfn
>> >>> >> >> > > > > to pfn mappings in the guest kernel. Since the same mfn 
>> >>> >> >> > > > > can be granted
>> >>> >> >> > > > > multiple times to the backend, finding the right pfn 
>> >>> >> >> > > > > corresponding to
>> >>> >> >> > > > > a
>> >>> >> >> > > > > given mfn can be difficult and expensive. Providing a 
>> >>> >> >> > > > > second mapping
>> >>> >> >> > > > > at
>> >>> >> >> > > > > a known address allow the kernel to access the page 
>> >>> >> >> > > > > without knowing
>> >>> >> >> > > > > the
>> >>> >> >> > > > > pfn.
>> >>> >> >> > > >
>> >>> >> >> > > > Is there a version of these patches for Xen 4.4 that I can 
>> >>> >> >> > > > test? The
>> >>> >> >> > > > restriction on duplicate pages is causing trouble for 
>> >>> >> >> > > > networking on
>> >>> >> >> > > > Mirage too
>> >>> >> >> > > > (http://roscidus.com/blog/blog/2014/07/28/my-first-unikernel/#tcp-retransmissions).
>> [...]
>> >> Checkout the branch grant_map_identity_4.4_2
>> >
>> > Thanks - it's working now!
>>
>> Update: if my VM uses the network and then exits quickly, dom0 gets
>> stuck.
>
> What do you mean by exit quickly? xl destroy domain?

The guest starts, sends a few packets and then exits (possibly before
the packets have been transmitted). This happens before "xl create"
manages to attach to the console.

>> It keeps logging:
>>
>> [  360.652715] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652796] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652835] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652874] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652910] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652947] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.652983] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>> [  360.653026] vif vif-1-0 (unregistered net_device): Page still
>> granted! Index: 9d
>>
>> The domain can't be destroyed:
>>
>> $ sudo xl list
>> Name                                        ID   Mem VCPUs      State   
>> Time(s)
>> Domain-0                                     0   512     2     r-----     
>> 185.7
>> (null)                                      10     0     1     --ps-d       
>> 0.1
>>
>> top shows the "xenwatch" process using 100% CPU and I have to reboot.
>>
>> A work-around is to use:
>>
>>   on_poweroff = 'preserve'
>
> Does the "Page still granted!" message go away after a while, or just
> keeps printing it?

It just keeps printing it.


-- 
Dr Thomas Leonard        http://0install.net/
GPG: 9242 9807 C985 3C07 44A6  8B9A AE07 8280 59A5 3CC1
GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA

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