Re: [PATCH] KVM: x86: Expose Predictive Store Forwarding Disable

From: Paolo Bonzini
Date: Mon Sep 27 2021 - 07:13:36 EST

On 27/09/21 12:59, Borislav Petkov wrote:
On Thu, Sep 23, 2021 at 08:15:28PM -0500, Babu Moger wrote:
Linux kernel does not have the interface to enable/disable PSFD yet. Plan
here is to expose the PSFD technology to KVM so that the guest kernel can
make use of it if they wish to.

Why should the guest kernel expose it if we said that for now we want to
disable it with the SSBD control?

Because the guest kernel needs to know which MSRs to write when you touch the SSBD prctl, so that PSFD is properly disabled *inside the guest*.