Re: [Xen-devel] [PATCH v4 0/7] unsafe big.LITTLE support

[Julien Grall <julien.grall@xxxxxxx>]

Hello,

On 08/03/18 06:15, Peng Fan wrote:
> Hi Stefano,
> On Fri, Mar 02, 2018 at 11:05:54AM -0800, Stefano Stabellini wrote:
> > Hi all,
> >
> > This series changes the initialization of two virtual registers to make
> > sure they match the value of the underlying physical cpu.
> >
> > It also disables cpus different from the boot cpu, unless a newly
> > introduced command line option is specified. In that case, it explains
> > how to setup the system to avoid corruptions, which involves manually
> > specifying the cpu affinity of all domains, because the scheduler still
> > lacks big.LITTLE support.
> >
> > In the uncommon case of a system where the cacheline sizes are different
> > across cores, it disables all cores that have a different dcache line size
> > from the boot cpu. In fact, it is not sufficient to use the dcache line
> > size of the current cpu, it would be necessary to use the minimum across
> > all dcache line sizes of all cores.  Given that it is actually uncommon
> > even in big.LITTLE systems, just disable cpus for now.
> >
> > The first patch in the series is a fix for the way we read the dcache
> > line size.
> I am trying the patchset, but I meet issue that Guest Big/Little with
> vcpu not working properly. As my current hardware has an issue
> which has fix in Kernel, 
> https://source.codeaurora.org/external/imx/linux-imx/commit/?h=imx_4.9.51_imx8_beta2&id=917cc3a8db2f3609ef8e2f59e7bcd31aa2cd4e59
Can you describe what you mean by not working properly? Also what is 
your setup? Did you pin the different vCPUs as requested by the 
documentation.
> I am not sure whether this issue cause DomU big/Little not work.
Well, I would recommend to speak with NXP whether this errata affects 
TLB flush for Hypervisor Page-Table or Stage-2 Page-Table.
> So wonder has this patchset been tested on Big/Little Hardware?
This series only adds facility to report the correct MIDR to the guest. 
If your platform requires more, then it would be necessary send a patch 
for Xen.
Cheers,

--
Julien Grall

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