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

[Tamas K Lengyel <tamas.lengyel@xxxxxxxxxxxx>]

On Fri, Jan 27, 2017 at 9:29 AM, Julien Grall <julien.grall@xxxxxxx> wrote:
> 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.
>

That would be fine by me. Wei, what do you think?

Tamas

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