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Re: [Xen-devel] [PATCH 6/7] xen/arm: Setup virtual paging for secondary CPUs in non-boot scenario


On 11/04/18 14:19, Mirela Simonovic wrote:
In existing code the paging for secondary CPUs is setup only in boot flow.
The setup is triggered from start_xen function after all CPUs are brought
online. In other words, the initialization of VTCR_EL2 register is done
out of the cpu_up/start_secondary control flow. However, the cpu_up flow
should be self-contained - it should fully initialize a secondary CPU,
because the cpu_up is used not only to bring a secondary CPU online on
boot, but also to hotplug a CPU during the system resume.
With this patch the setting of paging is triggered from start_secondary
function if the current system state is not boot. This way, the paging
will be setup in non-boot scenarios, while the setup in boot scenario
remains unchanged.

I am afraid that this is not correct. You can't assume that value chosen for VTCR by Xen at boot will fit this new CPU. So you have to check it is fine or park the CPU if there are any issue.

For more details have a look at [1].

[1] https://lists.xenproject.org/archives/html/xen-devel/2018-01/msg02482.html


Julien Grall

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