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 9:15 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.

>
> Now, if you are saying that on x86 it might be necessary to also clean the
> guest memory range. Then it would be worth to consider implementing the
> hypercall.
>

I'm not aware of this being needed on x86.

Tamas

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