linux-kernel - RE: [PATCH 1/2] x86/hyperv: Allow guests to enable InvariantTSC

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Message-ID: <CY4PR21MB01366C1E5858DA8BBDA3886AD79F0@CY4PR21MB0136.namprd21.prod.outlook.com>
Date:   Thu, 3 Oct 2019 23:15:39 +0000
From:   Michael Kelley <mikelley@...rosoft.com>
To:     Andrea Parri <parri.andrea@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "x86@...nel.org" <x86@...nel.org>
CC:     KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Sasha Levin <sashal@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H . Peter Anvin" <hpa@...or.com>
Subject: RE: [PATCH 1/2] x86/hyperv: Allow guests to enable InvariantTSC

From: Andrea Parri <parri.andrea@...il.com> Sent: Thursday, October 3, 2019 8:52 AM
> 
> If the hardware supports TSC scaling, Hyper-V will set bit 15 of the
> HV_PARTITION_PRIVILEGE_MASK in guest VMs with a compatible Hyper-V
> configuration version.  Bit 15 corresponds to the
> AccessTscInvariantControls privilege.  If this privilege bit is set,
> guests can access the HvSyntheticInvariantTscControl MSR: guests can
> set bit 0 of this synthetic MSR to enable the InvariantTSC feature.
> After setting the synthetic MSR, CPUID will enumerate support for
> InvariantTSC.
> 
> Signed-off-by: Andrea Parri <parri.andrea@...il.com>
> ---
>  arch/x86/include/asm/hyperv-tlfs.h | 5 +++++
>  arch/x86/kernel/cpu/mshyperv.c     | 7 ++++++-
>  2 files changed, 11 insertions(+), 1 deletion(-)
> 

As noted in a separate email, this patch is standalone, not 1 of 2 as
indicated in the subject line.  Modulo that,

Reviewed-by: Michael Kelley <mikelley@...rosoft.com>