Re: [Xen-devel] [PATCH RFC 0/N] xen: arm: rework early bring up

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2013-09-18 at 22:14 +0100, Julien Grall wrote:
> On 09/18/2013 09:22 PM, Ian Campbell wrote:
> > On Wed, 2013-09-18 at 21:00 +0100, Julien Grall wrote:
> >> On 09/18/2013 08:24 PM, Ian Campbell wrote:
> >>> On Wed, 2013-09-18 at 20:22 +0100, Ian Campbell wrote:
> >>>> On Wed, 2013-09-18 at 18:33 +0100, Julien Grall wrote:
> >>>>> On 09/17/2013 02:37 AM, Ian Campbell wrote:
> >>>>>> Hi,
> >>>>>>
> >>>>>> The following reworks early bring up on ARM to use a separate set of
> >>>>>> boot pagetables. This simplifies things by avoiding the need to bring 
> >>>>>> up
> >>>>>> all CPUs in lock step, which in turn allows us to do secondary CPU
> >>>>>> bringup in C code.
> >>>>>>
> >>>>>> Unfortunately the main bulk of this change is a single large patch 
> >>>>>> which
> >>>>>> is hard to decompose any further since it is basically pulling on the
> >>>>>> thread and then knitting a new jumper from it.
> >>>>>>
> >>>>>> With these changes Xen now absolutely requires that the bootloader 
> >>>>>> calls
> >>>>>> the hypervisor in HYP mode, the previous workarounds have been removed.
> >>>>>> For use on models a bootwrapper is now required. See
> >>>>>>           git://xenbits.xen.org/people/ianc/boot-wrapper.git xen-arm32
> >>>>>>           git://xenbits.xen.org/people/ianc/boot-wrapper-aarch64.git 
> >>>>>> xen-arm64
> >>>>>>
> >>>>>> I have implemented support for CPU bringup on the fastmodel vexpress
> >>>>>> platforms (v7and v8) here, I suppose it should work OK on a real
> >>>>>> vexpress too but I've not tried it.
> >>>>>
> >>>>> I have just tried the patch series on the versatile express and it
> >>>>> doesn't work. I'm using the u-boot from Andre and all the cpus already
> >>>>> boot in hyp mode (checked without this patch series).
> >>>>
> >>>> :-(
> >>>>
> >>>> The code should essentially the same as the old kick cpus, but
> >>>> reimplemented in C. The only difference I can spot is that the C version
> >>>> is kicking a single CPU at a time while the ASM version is kicking
> >>>> everyone at once. Does using send_SGI_allbutself instead work as a hack?
> >>>>
> >>>> Perhaps our idea of the CPUID is wrong or something? Your patches to
> >>>> fixup the logical CPU id stuff might help?
> >>
> >> I have found the issue, in send_SGI_mask we remove the offline CPUs with
> >> the following line:
> >>     mask &= cpumask_bits(&cpu_online_map);
> >>
> >> As the secondary cpu (assuming we have a board with only 2 cores) is not
> >> yet online, we can't send SGI with our code.
> >> I'm very surprised that the code works on the fast models.
> >
> > So am I, now.
> >
> > OK. So online mask == 0x1 and we are trying to wake mask 0x2, so the
> > actual target list we end up using is 0...
> >
> > The gic manual says "When TargetListFilter is 0b00, if the CPUTargetList
> > field is 0x00 the Distributor does not forward the interrupt to any CPU
> > interface." (footnote to table 4-21), so it shouldn't be waking
> > anything... It may be a model bug
> >
> >> To solve the issue, I think we need to create another helper which will
> >> send an SGI wihout removing offline CPUs.
> >
> > Looking briefly at the callchains leading to send_SGI_mask I don't see
> > any which deliberately pass an offline CPU (which would be pretty
> > non-sensical apart from this one case). So we could perhaps just remove
> > this check and make it the caller's problem.
> > Or maybe the right check is for cpu_possible mask or something similar
> > instead of online?
> 
> You are right, cpu_possible mask is better.
> I can modify this patch http://patches.linaro.org/20437/ to add the 
> check in gic_cpu_mask.

Sounds reasonable.
> 
> 



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