linux-kernel - Re: [PATCH 5/5] KVM: vmx: use MSR_IA32_TSX_CTRL to hard-disable TSX on guest that lack it

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Message-ID: <20191121022252.GX3812@habkost.net>
Date:   Wed, 20 Nov 2019 23:22:52 -0300
From:   Eduardo Habkost <ehabkost@...hat.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        jmattson@...gle.com,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH 5/5] KVM: vmx: use MSR_IA32_TSX_CTRL to hard-disable TSX
 on guest that lack it

On Mon, Nov 18, 2019 at 07:17:47PM +0100, Paolo Bonzini wrote:
> If X86_FEATURE_RTM is disabled, the guest should not be able to access
> MSR_IA32_TSX_CTRL.  We can therefore use it in KVM to force all
> transactions from the guest to abort.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>

So, without this patch guest OSes will incorrectly report "Not
affected" at /sys/devices/system/cpu/vulnerabilities/tsx_async_abort
if RTM is disabled in the VM configuration.

Is there anything host userspace can do to detect this situation
and issue a warning on that case?

Is there anything the guest kernel can do to detect this and not
report a false negative at /sys/.../tsx_async_abort?

-- 
Eduardo