linux-kernel - Re: [PATCH 1/5] KVM: x86: fix presentation of TSX feature in ARCH

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Date:   Mon, 18 Nov 2019 11:39:57 -0800
From:   Jim Mattson <jmattson@...gle.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        stable@...r.kernel.org, Aaron Lewis <aaronlewis@...gle.com>
Subject: Re: [PATCH 1/5] KVM: x86: fix presentation of TSX feature in ARCH_CAPABILITIES

On Mon, Nov 18, 2019 at 10:17 AM Paolo Bonzini <pbonzini@...hat.com> wrote:
>
> KVM does not implement MSR_IA32_TSX_CTRL, so it must not be presented
> to the guests.  It is also confusing to have !ARCH_CAP_TSX_CTRL_MSR &&
> !RTM && ARCH_CAP_TAA_NO: lack of MSR_IA32_TSX_CTRL suggests TSX was not
> hidden (it actually was), yet the value says that TSX is not vulnerable
> to microarchitectural data sampling.  Fix both.

I actually think kvm should virtualize IA32_TSX_CTRL for VMs that have
exclusive use of their cores (i.e. the same VMs for which we disable
MWAIT and HLT exiting).