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

[Thomas Leonard <talex5@xxxxxxxxx>]

On 6 August 2014 15:27, Stefano Stabellini
<stefano.stabellini@xxxxxxxxxxxxx> wrote:
> On Wed, 6 Aug 2014, Thomas Leonard wrote:
>> On 6 August 2014 15:14, Stefano Stabellini
>> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> > On Wed, 6 Aug 2014, Thomas Leonard wrote:
>> >> On 6 August 2014 14:46, Stefano Stabellini
>> >> <stefano.stabellini@xxxxxxxxxxxxx> wrote:
>> >> > 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.
>> >>
>> >> Here's a test case (tested on stable-4.4 with your patches:
>> >> https://github.com/talex5/xen/commits/stable-4.4):
>> >>
>> >> $ wget http://test.roscidus.com/static/breaks.xen
>> >>
>> >> $ cat > breaks.xl << EOF
>> >> name = 'breaks'
>> >> kernel = 'breaks.xen'
>> >> builder = 'linux'
>> >> memory = 256
>> >> on_crash = 'preserve'
>> >> vif = [ 'mac=c0:ff:ee:c0:ff:ee,bridge=br0' ]
>> >> EOF
>> >>
>> >> $ sudo xl create -c breaks.xl
>> >> Parsing config from breaks.xl
>> >> xenconsole: Could not read tty from store: No such file or directory
>> >> libxl: error: libxl_exec.c:118:libxl_report_child_exitstatus: console
>> >> child [0] exited with error status 2
>> >
>> > I cannot repro the issue even using "breaks.xen" as guest kernel.
>> > What dom0 kernel are you using?
>>
>> It's Linux 3.16-rc7, plus your patches:
>>
>>   https://github.com/talex5/linux/commits/master
>
> I realize that it's a bit old, but would you be able to test with a 3.14
> dom0? I am asking because 3.14 doesn't need my patches to work properly,
> so that would rule them out. You could also remove the corresponding Xen
> series.

It's not easy, because 3.14 doesn't have the mmc driver.

>> I'm testing on a CubieTruck, using this SD card image (includes
>> patched Linux and Xen):
>>
>>   http://blobs.openmirage.org/cubietruck-xen-iso.tar.bz2
>>
>> And yes, it's a Mirage unikernel.
>>
>> >> $ sudo xl list
>> >> Name                                        ID   Mem VCPUs      State   
>> >> Time(s)
>> >> Domain-0                                     0   512     2     r-----     
>> >> 335.1
>> >> (null)                                       8     0     1     --ps-d     
>> >>   0.1
>> >>
>> >>
>> >> > What if you delay the network initialization within the guest to a bit
>> >> > later?
>> >>
>> >> Yes, it's fine with a delay before using the network.
>> >
>> > Very interesting.
>>
>>
>>
>>
>> --
>> 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
>>



-- 
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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