On 05.02.19 00:06, Julien Grall wrote:
A57+A53.
I see the following in my log:
(XEN) alternatives: Patching with alt table 00000000002c6608 ->
00000000002c6c80
(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
A57?
Yes, the log says the workaround is applied to the big cores only. As it should
be.
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
environment.
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
regression?
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 :).
--
Sincerely,
Andrii Anisov.
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