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

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Date:   Mon, 27 Sep 2021 15:38:51 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     Babu Moger <babu.moger@....com>, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, hpa@...or.com, seanjc@...gle.com,
        vkuznets@...hat.com, wanpengli@...cent.com, jmattson@...gle.com,
        joro@...tes.org, tony.luck@...el.com, peterz@...radead.org,
        kyung.min.park@...el.com, wei.huang2@....com, jgross@...e.com,
        andrew.cooper3@...rix.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org
Subject: Re: [PATCH] KVM: x86: Expose Predictive Store Forwarding Disable

On Mon, Sep 27, 2021 at 02:54:08PM +0200, Paolo Bonzini wrote:
> There are other guests than Linux.  This patch is just telling userspace
> that KVM knows what the PSFD bit is.  It is also possible to expose the bit
> in KVM without having any #define in cpufeatures.h

Ok, then there's no need for the cpufeatures.h hunk.

> or without the kernel using it. For example KVM had been exposing
> FSGSBASE long before Linux supported it.

Ok, please do that for now then, if you want to expose it to other
guests. I'm sceptical they will have a use case for it either but I'm
always open to suggestions.

For the same reason as for baremetal, though, I wouldn't do that and do
that solely through the SSBD control but that's your call.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette