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

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Wed, 6 Aug 2014, Thomas Leonard wrote:
> 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.

I haven't seen anything like this and I cannot reproduce the issue on
unstable.
What if you delay the network initialization within the guest to a bit
later?


> >> 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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