Messages in this thread | | | Subject | Re: [PATCH 1/3] KVM: x86: use native MSR ops for SPEC_CTRL | From | Paolo Bonzini <> | Date | Fri, 23 Feb 2018 10:37:49 +0100 |
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On 22/02/2018 18:07, Konrad Rzeszutek Wilk wrote: >> Having a paravirt indirect call in the IBRS restore path is not a >> good idea, since we are trying to protect from speculative execution >> of bogus indirect branch targets. It is also slower, so use >> native_wrmsrl on the vmentry path too. > But it gets replaced during patching. As in once the machine boots > the assembler changes from: > > callq *0xfffflbah > > to > wrmsr > > ? I don't think you need this patch.
Why not be explicit? According to the spec, PRED_CMD and SPEC_CTRL should be passed down to the guest without interception so it's safe to do this. On the other hand, especially with nested virtualization, I don't think you can absolutely guarantee that the paravirt call will be patched to rdmsr/wrmsr.
Paolo
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