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

[Julien Grall <julien.grall@xxxxxxx>]

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.
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.
Cheers,

--
Julien Grall

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