Re: [Xen-devel] [PATCH] xen/arm: flush icache as well when XEN_DOMCTL_cacheflush is issued

[Julien Grall <julien.grall@xxxxxxx>]

Hi Tamas,

On 27/01/17 16:23, Tamas K Lengyel wrote:
> On Fri, Jan 27, 2017 at 9:15 AM, Julien Grall <julien.grall@xxxxxxx> wrote:
> > Hello,
> >
> > On 27/01/17 15:52, Tamas K Lengyel wrote:
> > > Well, yes, only ARM could _should_ call this function. The comment I
> > > think is important to tell the user don't expect it to do anything on
> > > x86.  Doesn't mean they can't call it though - if that was the case it
> > > would be wrapped in an ifdef like all the other architecture specific
> > > bits in the header. I would think that's pretty straight forward. No
> > > objection to clarifing the comment though if it helps.
> >
> > If you looked at the commit log, the #ifdef was added to avoid calling the
> > hypervisor for nothing and therefore saving few hundred cycles bit of time.
> > Technically speaking, this helper abstracts the architectural behavior of
> > the cache. So it makes sense to call it on x86 even if it is a nop.
> Except that on x86 the user should be aware that it returns an error,
> which is normal and can be ignored.
It looks like the current callers does not check the return. However, it 
would more make sense to return 0 if we expect nothing to be done rather 
than -ENOSYS.
Regards,

--
Julien Grall

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