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What is the difference between the IBRS suffix and no-suffix CPU models in QEMU? Which one should I choose?

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The CPU model with the -IBRS suffix has Spectre V2 (CVE-2017-5715) mitigation turned on by default in the guest.

The CPU model without the suffix has the mitigation off by default.

Unless you have a specific, extremely compelling reason to not have this mitigation, you should always use the IBRS variant of the virtual CPU.

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    Does this fix have any kind of impact on performances? Commented Nov 11, 2020 at 21:49
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    @user2965433 There's the normal performance impact of Spectre mitigations. You can measure it if you really need to, but it should not be significant enough to bother. Commented Nov 11, 2020 at 21:53

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