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Re: [Xen-devel] RT Xen on ARM - R-Car series

On Tue, 12 Feb 2019, 19:21 Andrii Anisov, <andrii.anisov@xxxxxxxxx> wrote:
Hello Julien,


Sorry for the formatting.

On 07.02.19 12:59, Julien Grall wrote:
> In that case I would prefer if we don't keep the runstate mapped.

Actually I'm going to see runstate update impact on the context switch time. For that I will extend TBM with runstate setup.
I really do not like a bunch of `copy_to_guest()` done on each context switch because of runstate.

Please provide more meaningful arguments other than "I don't like it". I provided potential drawbacks on my previous e-mails that you haven't yet addressed.

FWIW, Volodymyr had the same argument on OP-TEE and I requested to avoid the global mapping. I haven't seen any concern for performance devredation afterwards. Please feel free to come with numbers here.

If you are against runstate mapping, I'd like to fit runstate into a page, than access it directly from the hypervisor.

This is not really a policy in Xen. If the guest cares about it, it can ensure that the runstate does not cross a page boundary.


Andrii Anisov.
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