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Re: [Xen-devel] [PATCH MM-PART2 RESEND v2 14/19] xen/arm32: mm: Avoid cleaning the cache for secondary CPUs page-tables



Hi,

On 05/06/2019 11:19, Julien Grall wrote:
On 05/06/2019 00:11, Stefano Stabellini wrote:
On Tue, 14 May 2019, Julien Grall wrote:
The page-table walker is configured to use the same shareability and
cacheability as the access performed when updating the page-tables. This
means cleaning the cache for secondary CPUs runtime page-tables is
unnecessary.

All right. Is there an explicit configuration for the shareability and
cacheability used by the page-table walker or is it specified as such in
the Arm Arm?

See the configuration of TCR_EL2, I can mention it.

Also, isn't it possible that CPUs on a different cluster
(big.LITTLE) would have issues with this if the cache could be split
between the two clusters?

Gentle ping, can you please clarify your question.


I don't understand this... Cache should be coherent when a CPU leaves EL3.
But we already share some bits of the page tables between the processor (see create_xen_page_tables). So I don't see where there is a possible problem here.

Cheers,

--
Julien Grall

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