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

On 05.02.19 00:06, Julien Grall wrote:

I see the following in my log:

     (XEN) alternatives: Patching with alt table 00000000002c6608 -> 
     (XEN) CPU0 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
     (XEN) CPU2 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
     (XEN) CPU3 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry
     (XEN) CPU1 will call ARM_SMCCC_ARCH_WORKAROUND_1 on exception entry

Cortex-A53 should not be affected by spectre v2, so I imagine they are only for 
Yes, the log says the workaround is applied to the big cores only. As it should 

It is going to be hard to disable the workarounds by default. But we can 
consider to provide host-wide or per-guest option to disable them on trusted 
We have to get numbers first than decide how to proceed.

Also, when you mean possible, does it mean you haven't looked the performance 
We have a preliminary results about performance drop with xen4.12-unstable 
comparing to a our system with 4.10.

A lot of patches have not been backported in Xen 4.10 (including 
Spectre/Meltdown) that will definitely fix hole but may have an impact on the 
performance. There were not backported because of performance reason but 
because of the complexity of the port and seemly lack of interest.
I know that story. But customers are customers. And performance drop in the 
next SW version is always painful for them.
So we need a good explanation (which Spectre mitigation might be), or better to 
show up no performance drop :).

Andrii Anisov.

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